Glossary of AV/IT Terms

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This Glossary of AV/IT Terms is crowdsorced. Extron has graciously provided the majority of terms. Additional terms have been provided by Paul Zielie, Consulting Solutions Architect at AVCoIP LLC, as well from our articles. This is an ongoing effort. 


4K - “4K” refers to video devices, services or programs with 3840x2160 resolution, or over 8 million individual pixels. That is more than four times the resolution of Full HD sets. 4K UHD includes a wide range of benefits other than increased resolution.

5Play - A feature set of HDBaseT that enables delivering video, audio, Ethernet, control signals, and power over a single 100m / 328ft CAT5e / 6 cable. Also see “HDBaseT.”


A/D - Analog to Digital (converter). A device that converts an analog signal to a digital value.

AACS – Advanced Access Content System - A digital rights management standard utilized with Blu-ray Disc and other optical formats. AACS incorporates two parts: a set of embedded decryption keys within the source device, and a set of keys encoded in the content that describes each of the playback devices licensed to utilize the content. This approach allows copyright holders to revoke the keys of a particular source device, thus preventing it from playing back future content. AACS also provides for a managed copy system, that is, a mechanism by which one or several, but not an unlimited number of copies can be legally made as backups, for storage on a media server, or for use on a portable device. The ICT – Image Constraint Token is a provision within AACS that allows the content provider to limit analog output resolutions.

AAP™ AV Connectivity Modules - Mountable metal plates available in hundreds of models offering popular pass-through audio, video, phone, data, power, and control connectors. Active AAP modules are also available for power, control, and long distance signal transmission. Along with mounting options for maximum flexibility in placing connectors and controls within reach, these interchangeable components fit together to create an attractive and completely customizable AV connectivity solution.

Absorption - The attenuation of light as it passes through fiber, similar to the resistive loss of an electrical signal as it passes through cable. Absorption is caused by impurities and defects in the fiber.

AC - Alternating Current. Electron flow that changes direction alternately.

AC coupled - A circuit design that does not pass the DC component of a signal, therefore it ignores DC offsets.

AC-3 - See "Dolby® Digital."

Acceptance Angle - In fiber optics, this is the critical angle, measured from the center axis of the fiber. Incoming light must be directed below this angle in order to enter the core of the fiber and propagate along its length through total internal reflection.

Active crossover - A circuit that separates the audio signal into the appropriate frequency bands for the woofer, midrange, and tweeter. An active crossover is placed in the signal path ahead of the amplifier, where a passive crossover is placed between the amplifier and the speaker.

ADC - Analog to Digital Converter. A device that converts analog signals to digital signals.

Additive color process - Also called “RGB.” A color generation process used in video that combines red, green, and blue to make all colors. All three colors (red, green, and blue) at 100% combine to make white on a video screen; the absence of all three colors (0%) makes black. Also see "Subtractive color process."

Adobe RGB - A color space specification developed by Adobe® Systems, Inc., offering a wider color gamut than sRGB. Adobe RGB is supported in Photoshop® and other Adobe software, as well as some digital cameras, printers, scanners, and displays.

ADSL - Asymmetrical Digital Subscriber Line. One of a number of DSL technologies, and the most common one. ADSL is designed to deliver more bandwidth downstream (from the central office to the customer site) than upstream.

ADSP™ - Advanced Digital Sync Processing™. Using sync processing to allow centering control (H-shift or V-shift) can create problems with some display devices because of the sync delay. This means the digital projector user may have to choose between a stable sync and centering control. Extron's ADSP restores the original sync timing relationship for a stable sync signal while allowing centering control.

ADTV - Advanced Definition Television. An early HDTV system proposed by the Advanced Television Research Consortium in 1992. Now superseded by US HDTV standards.

AEC - Acoustic Echo Cancellation - Echo occurs when audio from a talker in the far end is received and amplified into the near end listener’s room, with that sound then being picked up by microphones in the near end acoustic space and sent back to the far end. The amount of signal sent back to the far end talker can be substantial, and with the added transmission delay, the result is an echo effect that can seriously compromise communication in a teleconference or videoconference. Acoustic Echo Cancellation processor removes the potential echo signal at the near end mic channel by comparing it to the received signal from the far end, designated as the “reference,” and then creating an adaptive filter to cancel the potential echo before it is sent back to the far end.

Aerial Cables - Optical fiber cables designed for outdoor installations on aerial supporting structures such as poles. They are specifically designed to withstand adverse conditions such as wind and ice loading, pollution, UV radiation, thermal cycling, stress, and aging.

AES – Advanced Encryption Standard - A data encryption standard adopted by the US Government and approved by the National Security Agency for top secret information. DCP, LLP, the licensing agency for HDCP, has adopted AES 128 encryption for the new HDCP 2.0 standard.

AES/EBU - Audio Engineering Society/European Broadcasting Union. A digital audio transfer standard. The AES and EBU developed the specifications for the standard. The AES/EBU digital interface is usually implemented using 3-pin XLR connectors, the same type of connector used in a professional microphone. One cable carries both left- and right-channel audio data to the receiving device. Also see "AES3."

AES3 - A digital audio standard defined by the Audio Engineering Society. The standard specifies several basic physical interconnections between devices:
- Balanced - 3-conductor, 110 ohm cabling with an XLR connector, typically referred to as “AES/EBU audio.”
- Unbalanced - 2-conductor, 75 ohm coaxial cable with an RCA connector, typically used in consumer audio applications. In many consumer products such as DVD players and A/V receivers, this is often referred to as a “digital coaxial” connection type.
- AES-3id - A professional version of the 2-conductor 75 ohm coaxial cable terminated with a BNC connector. AES3 unbalanced and AES-3id audio can be switched or routed using a video switcher with a minimum of 150 MHz (-3 dB, fully loaded) video bandwidth.
- Optical – Plastic optical fiber using an F05 style connector, typically used in consumer audio applications. In many consumer products, this is often referred to as a “digital optical” connection type. TOSLINK is the most common implementation of this connection type.

AFL™ - Accu-RATE Frame Lock™. Extron's patented method of eliminating image tearing which is associated with scaling, especially when motion video is involved, and occurs when the input frame rate is slower or faster than the output frame rate and part of the old frame and part of the new frame are displayed at the same time during a refresh cycle. Extron Accu-RATE Frame Lock sets and locks the output frame rate to the input frame rate of a designated input and produces a tear-free output in a seamless switching system.

AGC - Automatic Gain Control. A circuit used to automatically control the level of the recorded or transmitted signal. It is sometimes called Automatic Level Control (ALC), or Automatic Volume Control (AVC).

Air Blown Fiber – ABF - Optical fiber installed through special tube cables by means of using pressurized air or nitrogen to "blow" bundles of fibers through individual tubes within the cable. Tube cables are usually pre-installed at the premises before installation of air blown fiber.

Air Polish - In fiber optics, this is the first step in polishing the connector using special fine grit film, after the fiber has been cleaved.

ALC - Automatic Level Control. In audio recording, a circuit used to control the volume or level of the recorded signal automatically without distortion due to overload. Sometimes called Automatic Gain Control (AGC), or Automatic Volume Control (AVC).

Aliasing - (1) Aliasing occurs when smooth curves and lines become rough or jagged because of a lower resolution device, or by an event. (2) In analog video, aliasing is typically caused by interference between the luma and chroma frequencies or between the chroma and field scanning frequencies. It appears as a moiré or herringbone pattern, straight lines that become wavy, or rainbow colors. Also see “Cross color.” (3) In digital video, insufficient sampling or poor filtering of the signal causes aliasing. Defects typically appear as jagged edges on diagonal lines and twinkling or brightening in picture detail.

All Dielectric - In fiber optics, this denotes the presence of only dielectric, or non-metal elements.

AM - Amplitude Modulation. A method of radio transmission, by which the information part of the signal causes the amplitude of a carrier frequency to vary without affecting the frequency.

Ambient Sound Level - Any environmental or background sound that exists before a new sound source is added. For example, in a school classroom, ambient sound may come from an adjacent hallway or playground, HVAC system, room lights, or another classroom. Ambient sound must be taken into consideration when designing a sound support system.

Ambient Sound List - Any environmental or background sound that exists before a new sound source is added. For example, in a school classroom, ambient sound may come from an adjacent hallway or playground, HVAC system, room lights, or another classroom. Ambient sound must be taken into consideration when designing a sound support system.

American National Standards Institute (ANSI) - ANSI is a private, non-profit organization that administers and coordinates the voluntary standardization and conformity assessment system in the US.

Amp - Ampere. The international base unit of electrical current that represents the rate flow of electric charges through a conductor. Symbolized by “A.” 1 amp is equal to the steady current produced by 1 volt applied across a resistance of 1 ohm.

Amplifier - An electronic device used to increase the voltage amplitude of a signal.

Amplifier classifications - Audio amplifiers are typically described by “class”. There are four primary classes used in A/V system designs: A, B, A/B, and D.

Amplitude - The level or strength of a signal as measured by the height of its waveform. Electronic waveforms can be displayed and measured on an oscilloscope.

Amplitude Modulation – AM - Amplitude modulation is also employed in fiber optics applications, in which light acts as a carrier signal with its amplitude varying in accordance to the signal being conveyed.

Anaerobic - For fiber optics, this describes a method of bonding between optical fibers via a non-heat, intrinsic chemical reaction within the adhesive material. By definition, an anaerobic adhesive does not require air to cure.

Analog - A continuously varying action or movement that takes time to change from one position to another. Standard audio and video signals are analog. An analog signal has an infinite number of levels between its highest and lowest value (unlike digital, in which changes are in steps).

Analog control - A method using continuously varying voltage levels to provide control of equipment.

Analog Sunset - When used colloquially, may refer to the general trend of digital video technologies displacing analog, such as when US broadcast television switched to digital transmission, or the increasing use of DVI, HDMI, and DisplayPort video on PCs instead of RGB, etc. In a narrowly defined legal sense, the analog sunset refers to AACS licensing restrictions placed on Blu-ray Disc players where licensed players produced after 2010 must limit analog video output to standard definition, and licensed players produced after 2013 must not output any analog video, when playing protected content.

Anamorphic - A type of lens or adapter designed to produce a widescreen image from a condensed image on the film. Trademarked anamorphic systems include CinemaScope, VistaVision, and Panavision.

Anamorphic DVD - A DVD with a widescreen video image that has been horizontally squeezed to fit into a standard video frame, resulting in an image with higher resolution than letter boxing can produce. Anamorphic DVDs are designed for optimal display on 16:9 widescreen displays or video scalers with an anamorphic squeeze mode.

Anechoic chamber - An acoustic space without echo or reverberation. Often used for the acoustic testing of microphones and loudspeakers.

Angle of Incidence - The angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal

Angled Physical Contact – APC - A specific technique for singlemode fiber applications where the endface of the fiber or ferrule is cut and polished at an 8 degree angle in order to increase contact surface area and help minimize return loss. APC connectors are typically green in color and are not used in multimode applications. They are also rarely used in digital applications. APC polished connectors are not compatible with UPC, SPC, or PC polished connectors. Intermixing APC polished connectors with UPC/SPC/PC polished connectors can damage the fiber optic cable or equipment.

Animations - Animations consist of motion image sequences produced synthetically on video processing or computing systems.

ANSI lumen - The common unit of measurement for the light output of a projector, as measured by ANSI, the American National Standards Institute. The higher the ANSI lumen rating, the brighter the projector. In general, there needs to be about a 30% differential in the ANSI lumen rating before the human eye can really notice an appreciable difference in brightness when two projectors are shown side by side. Determining the lumen output for a given application depends on five factors, (1) the level of ambient room light (2) the size of the audience, (3) the size of the projected image, (4) the quality of the projection screen, and (5) the amount of detail in the presentation material. Also see "Lumen."

Antialiasing - A technique in computer graphics for smoothing jagged edges by blending shades of color or gray along the edges. Some video devices, such as character generators, have an antialiasing feature to minimize aliasing through filtering and other techniques. Also see "Aliasing."

Aperture - The opening, usually an adjustable iris, that controls the amount of light passing through a lens. In motion picture cameras, the mask opening that defines the area of each frame exposed. In motion picture projectors, the mask opening that defines the area of each frame projected.

Aperture grill - A grill-like feature of Sony Trinitron CRT monitors and others licensed by Sony that controls the number of electrons hitting the phosphor coating on the screen.

Apple Cinema Display - One of the first very high resolution monitors on the market and one of the first to utilize a dual-link DVI connection. The 30" version provides a native resolution of 2560x1600 pixels.

Aramid Yarn - A woven strength member, with Kevlar® as a common brand, incorporated into fiber optic cable that provides tensile strength and protection.

Arc - In fiber optics, the discharge that may occur between the two electrodes of a fusion splicer.

Armored Cable - Cable that is protected with metal sheathing or rods below or between the cable jacketing to protect from damage due to adverse outdoor factors such as rodent attack.

ARP - Address Resolution Protocol. A protocol for assigning an IP address to a device based on the device’s MAC (Media Access Control), or physical machine address, that maintains a table showing the correlation between the two.

Artifacts - Any error in the perception or representation of any visual or aural information introduced by the involved equipment. Image artifacts appear as deviations from the original in the delivered image in video streaming systems.

ASCII - American Standard Code for Information Interchange. The standard code consisting of 7-bit coded characters (8 bits including parity check) used to exchange information between data processing systems, data communication systems, and associated equipment. The ASCII set contains control characters and graphic characters.

Aspect ratio - The relationship of the horizontal dimension to the vertical dimension of an image. In viewing screens, standard TV is 4:3, or 1.33:1; HDTV is 16:9, or 1.78:1. Sometimes the “:1” is implicit, making TV = 1.33 and HDTV = 1.78.

ASTA - Active Sync Termination Adapter. A VGA-style (15-pin HD connector) adapter that provides active circuits that shape up the horizontal and vertical sync signals. This adapter may be used to eliminate jitter and/or intermittent tearing in the displayed image. Most small digital projectors are designed to be near the video source and may not provide impedance matching.

Asynchronous - Intermittent, not synchronized or continuous. A conversational type of communication that allows the parties at each end to talk when they like instead of at a prescribed time. Used in videoconferencing.

ATM - Asynchronous Transfer Mode. A standardized digital data transmission technology that is a cell-based switching technique which uses asynchronous time division multiplexing. This is the core protocol used over the SONET/SDH backbone of the ISDN (Integrated Services Digital Network).

ATSC - Advanced Television Systems Committee. The ATSC was formed to establish voluntary technical standards for advanced television systems, including digital high definition television (HDTV). The ATSC is supported by its members, who are subject to certain qualification requirements.

Attenuate/Attenuation - To reduce the amplitude (strength) or current of a signal.

Attenuation - In fiber optics, this is the loss of optical power as light passes through a fiber optic path. This loss can occur due to absorption, scattering, and excessive bending within the fiber, and can also be attributed to optical components such as connectors, splices, and splitters. Attenuation is usually expressed in dB/km.

Audio - Of or concerning the electronic transmission of sound, specifically the electrical currents representing a sound. (CF. Sound)

Audio follow - A term used when audio is tied to other signals, such as video, and they are switched together. The opposite of “breakaway.”

Audio frequency - Frequencies within the range of human hearing, about 20 Hz to 20 kHz.

Audio summing amplifier - A device that converts two-channel stereo audio signals into balanced/unbalanced one-channel mono audio signals.

Auto-focus - Automatic focus. A device in a projector or camera that uses light reflected from a surface to focus the image.

Auto-Image™ - An Extron technology for scan converters and signal processors that simplifies setup by executing image sizing, centering, and filtering adjustments with a single button push.

Auto-input switching - The feature that enables a product to detect which input has an active sync signal and switch to that input.

Automatic convergence - The automatic alignment of the red, green, and blue color images on a screen.

Automatic sync stripping - The automatic removal of sync signals from video channels. Typically, this is associated with removing the sync signal from the green channel, but it may apply to stripping the sync from all three video channels (Red, Green, and Blue).

Autosizing - Automatic picture sizing adjustment to compensate for different display modes, thus enabling the display system to center the picture and fill the screen.

Autoswitching - The feature that enables a product to detect which input has an active sync signal and switch to that input.

AV - Audio visual, or audio video.

Avalanche Photodiode – APD - A type of photodiode, or optical signal transducer that converts light to an electrical signal, used in fiber optic receivers.

AVoIP (Audio Video over Internet Protocol) - Audio Video over Internet Protocol – AVoIP – AV over IP – is a method of transmitting digital audio and video over standard network switching and routing equipment. The digital audio and video are broken into segments and encapsulated in standard internet protocol packet headers. These Internet Protocol or IP packets can then be carried from a transmitter to a receiver over standard networking equipment across a local network or over the Internet. Modern AVoIP systems typically include the exchange of additional data such as USB, RS-232, IR, and control signals along with the audio and video. These systems commonly incorporate encoders and decoders to compress and decompress the audio, video, and data to improve network efficiency.

AWG - American Wire Gauge. A standard measurement for wire conductor diameter.


Back porch - The time in a composite video signal that is between the trailing edge of the sync pulse and the trailing edge of the blanking pulse (before the video information). Also see "Blanking."

Backbone - The primary transmission network for telecommunications that connects between key locations and branches off to buildings and other facilities.

Backreflection - Light within an optical fiber that is reflected back toward the source. This typically occurs at interfaces between the fiber and the connector where an air gap causes the reflection.

Backscattering - The portion of light within an optical fiber that is scattered back toward the source.

Balanced audio - The audio signal that is carried on three wires (or five wires for stereo pair), with two of them carrying the same signal but with reversed polarity, and a third wire for shielding. Since the two signal wires would pick up virtually identical noise from outside (common mode noise), and that noise can be canceled out at the receiving end by a differential amplifier, the balanced audio is much less susceptible to hum and interference from long cable runs.

Band pass filter - A filter that allows a specific range to pass. The bandpass frequencies are normally associated with frequencies that define the half power points, i.e. the -3 dB points. In multi-driver speaker systems, for example, the mid-range driver may be fed by a bandpass filter.

Band reject filter - A filter that combines the characteristics of a low pass and a high pass filter that is used to block a narrow band of frequencies, while allowing frequencies above or below this band to pass. (i.e. notch filter)

Banding - A video problem of dark bars appearing across the displayed image in areas where there is movement.

Bandwidth - The total range of frequencies required to pass a specific signal without significant distortion or loss of data. In analog terms, the lower and upper frequency limits are defined as the half power, or -3 dB signal strength drop, compared to the signal strength of the middle frequency, or the maximum signal strength of any frequency, expressed as xx Hz to xx kHz (or MHz) @ -3 dB. In digital terms, it is the maximum bit rate at a specified error rate, expressed in bits per second (bps). A device's bandwidth should be wider than the highest possible bandwidth of the signals it may handle. (In general, the wider the bandwidth, the better the performance. However, bandwidth that is too wide may pass excessive noise with the signal.)

Barrel connector - An adapter used to connect two coax-type connectors of the same gender.

Baseband - A prime signal such as composite video, component video, and audio with its own path but is not modulated onto a carrier signal or combined with other signals on a path. An unmodulated signal or band of signals. The video signal seen on a waveform monitor is a baseband video signal.

Baud - Named for J. M. E. Baudot, the inventor of the Baudot telegraph code. The number of electrical oscillations per second, called baud rate. Related to, but not the same as, transfer rate in bits per second (bps).

Bend Loss - In fiber optics, the attenuation of light as it passes through a fiber with excessive bending. Macrobending and microbending both contribute to bend loss.

Bend radius - The smallest radius at which an optical fiber or fiber optic cable can be bent without introducing attenuation or damage to the fiber.

Bending - A video problem when the top of the screen hooks, bends, or tears to the side. Also known as “hooking.”

BER - Bit Error Rate. The rate at which bit errors are experienced across a data connection.

Best Effort - Describes a network service in which the network does not provide any guarantees that data is delivered or that a user is given a guaranteed quality of service level or a certain priority.

B-Frame - Bi-directionally predictive coded picture. Contains predictive, difference information from the preceding and following I- or P-frame within a GOP. Data preceeding or following the B-frame are required to recreate video information in a B-frame.

Bidirectional - The ability to move, transfer or transmit in both directions.

Binary - A numbering system using base-2. Each digit is represented by a 1 or a 0 (on or off).

Binary code - A coding system using the digits 0 and 1 to represent a letter, numeral, or other character in a computer. For example: the character “A” in ASCII code becomes 0100 0001 in binary.

B-ISDN - Broadband Integrated Services Digital Network. A special version of ISDN that uses fiber optics and can transfer at 1.5 megabits per second. Also see "ISDN."

Bit - The shortened form of “binary digit” (0 or 1). A bit is the smallest unit of information in a computer.

Bit depth - The number of bits per pixel. Bit depth determines the number of shades of gray or variations of color that can be displayed by a computer monitor. For example, a monitor with a bit depth of 1 can display only black and white; a monitor with a bit depth of 16 can display 65,536 different colors; a monitor with a bit depth of 24 can display 16,777,216 colors

Bit Error - Bit error indicates the number of bits of a data stream over a communication channel that have been altered. A bit error can result in unusable data or the corruption of an image in video streaming solutions.

Bit Error Rate – BER - The fraction of bits that were transmitted with errors, expressed at the ratio of incorrectly to correctly transmitted bits. BER is used to assess transmission accuracy in a fiber optic system.

Bit map - A method of graphic display using rows and columns of dots, or pixels. Each pixel location corresponds to a specific location in memory.

Bit Rate - The number of bits that are conveyed or processed per unit of time. The bit rate is quantified using the bits per second (bit/s or bps) unit, often in conjunction with an SI prefix such as kilo- (kbit/s or kbps), mega- (Mbit/s or Mbps), giga- (Gbit/s or Gbps).

Black - The darkest visible surface created by the absorption of all incident light and color. In video, the absence of picture information.

Black and white - Monochrome (one color) or luma information. In the color television system, the black and white portion of the picture has to be one color: gray, D6500 or 6500° K, as defined by x and y values in the 1939 CIE color coordinate system. Commonly referred to as “D65.”

Black level - More commonly referred to as “brightness,” the black level is the level of light produced on a video screen. The level of a picture signal corresponding to the maximum limit of black peaks. The bottom portion of the video wave form, which contains the sync, blanking, and control signals. The black level is set by the brightness control.

Blackburst - The video waveform without the video elements. It includes the vertical sync, horizontal sync, and the chroma burst information. Blackburst is used to synchronize video equipment to align the video output. One signal is normally used to set up an entire video system or facility. Sometimes it is called House sync.

Blackburst generator - A special device for calibrating video equipment by generating a composite video signal with a totally black picture. This blackburst signal is used to synchronize video equipment to provide vertical interval switching. It also provides black level and chroma burst information for maintaining uniform video levels and color information.

Blanking - The interval after the electron beam completes a scan line and returns (retraces) to the left. During this time, the beam must be turned off (horizontal blanking). Similarly, when the last line has been scanned at the bottom of the screen, the beam must return to the upper left (vertical blanking).

Blanking adjustment - The ability to adjust the degree of blanking on the image. This is useful for eliminating artifacts such, as closed caption noise or improperly adjusted VTR head-switching that can be seen at the top or bottom of a displayed image.

Blanking level - The level of a video signal that separates the picture information from the sync information. The level of the front and back porches is 0 IRE units. To blank the video signal, the video level is brought down to the blanking level so nothing is visibly displayed, while the electron beam returns (retraces) to the start of the next line.

Blooming - Most noticeable at the edges of images on a CRT, blooming is when the beam hitting the screen is too intense and overdrives the phosphors. The edges of an image seem to exceed its boundaries. Thin lines and sharp edges may look thick and fuzzy. This may be caused by the contrast being set too high, or by a high voltage problem.

Blu-ray Disc - An optical disc storage medium developed by Sony as the replacement for DVD. Blu-ray is capable of storing high-definition video, audio, and data with a capacity of 50GB per disc. Blu-ray players are backward-compatible with standard DVDs and audio CDs.

BME - Basic Module Enclosure. Some large devices, such as the Extron Matrix 3200/6400/12800 Switchers, may be contained in more than one enclosure, yet function as a single device. Each physical box, or enclosure, is called a BME.

BNC - Bayonet Neill-Concelman. A cable connector used extensively in television and named for its inventors. A cylindrical bayonet connector that operates with a twist-locking motion. To make the connection, align the two curved grooves in the collar of the male connector with the two projections on the outside of the female collar, push, and twist. This allows the connector to lock into place without tools.

Boot/Boot-up/Bootstrap - The initialization process a system goes through after power comes on. It may also occur as part of resetting. To start a new beginning, you “pull yourself up by your bootstraps.”

Bow - The curving of scan lines in the center of the image.

Breakaway - The ability to separate audio and video signals for switching them independently. For example, the audio and video signals from one source may break away and be switched to two different destinations. This is the opposite of the term “audio follow.”

Breakdown voltage - The voltage level at which the insulation between conductors fails and electricity flows between the conductors.

Breakout Cable - In fiber optics, a cable comprising a bundle of several jacketed fibers, with the fibers separated from the bundle at one end to facilitate installation into panels and other equipment. The fibers are individually jacketed.

Breakout Kit - In fiber optics, a kit used to create a breakout cable from bundled fiber optic cable.

Breezeway - The early part of the back porch portion of the video signal. The area between the horizontal sync pulse and the color burst.

Bridge - A device that connects two network segments together, which may be similar or dissimilar, such as Ethernet and Token Ring. A bridge is inserted in the network to keep traffic contained within the segments to improve performance.

Bridge (or multipoint bridge) - A device that allows multiple systems to dial in and participate in a single videoconference.

Bridging (or Bridged) Audio - Some stereo amplifiers are designed to allow “bridging” or combining the power output of two channels into one channel. Bridging allows the amplifier to drive one speaker with more power than the amp could produce for two speakers. Not all amplifier designs allow bridging, however. NEVER attempt bridging of an amplifier without first consulting the manufacturer’s documentation and instructions.

Brightness - Usually refers to the amount or intensity of video light produced on a screen without regard to color. Sometimes called “black level.”

Brightness control - The control on a television monitor that increases or decreases the radiance of an image.

Brightness ratio - The difference between the lightest (whitest) and darkest (blackest) areas in an image. The wider the brightness ratio, the wider the contrast ratio.

Brightness signal - Same as the luma (Y) signal; a signal that carries information about the light intensity at each point in the image.

Broadband - A communications channel that has greater bandwidth than a voice-grade line and is capable of greater transmission rates.

Broadcast - The operation of sending network traffic from one network node to all other network nodes.

BT.2020 - Formally ITU-R Recommendation BT.2020, and also known as Rec. 2020. The international standard for Ultra HD video that specifies the 3840x2160 and 7680x4320 resolutions, color space parameters that define a much wider color gamut than previous specifications, frame rates up to 120 fps, color bit depth up to 36 bits per pixel, digital color encoding, chroma subsampling, and more.

BT.709 - Formally ITU-R Recommendation BT.709, and also known as Rec. 709. The international standard for high-definition video that specifies resolutions, frame rates, digital color encoding, color space parameters, and more.

Buffer - 1) In electronics, a circuit such as a unity gain amplifier used to isolate the signal source from the load. A buffer can be used for digital or analog signals. 2) In digital systems, a region of memory used to temporarily hold data while it is being delivered from one process to another.

Buffer Coating - A plastic coating applied to an optical fiber that provides protection from moisture or damage, as well as handling during the manufacturing of fiber optic cable.

Buffer Tube - An additional plastic tubing around the buffer coating of an optical fiber that provides added protection. This tubing is typically colored.

Burn-in - In a video or plasma display, this term describes what happens when an image has been displayed too long, a permanent image is burned into the screen phosphor.

Burst - A sequence of data delivered in a short period of time. Network designs must account for both predictable data traffic and bursts of traffic.

Burst error - Consecutive data errors that occur suddenly. If errors spanning several bytes occur, complete decoding at the receiving end may not be possible even if error correction is applied. As a measure against burst errors, methods such as interleaving are used. Errors occurring on real world networks are typically burst errors.

Bus - A path for transporting voltages, signals, or a ground between the different sections of an electronic device, such as a data bus between a CPU and memory or a peripheral device. Its width is determined by the number of lines (conductors) that make up the bus, and its speed (data transfer rate) is determined by the circuits that drive the lines.

Butt Closure - A product that serves to provide protection to fiber optic cable splices and terminations within a sealed enclosure.

Butterworth filter - A filter characterized by smooth response at all frequencies and -6 dB per octave decrease from the specified cutoff frequencies. Butterworth filters are maximally flat; that is, they pass the selected band of frequencies (the pass band) without distortion.

Byte - A group of bits processed together – the more bits in a byte, the more distinct values in that byte. More Info: A camcorder that offers 10-bit digital processing has 10 bits in a byte, which means each byte has 10 on/off switches, with “1” being on and “0” being off. In a binary system, you take the number two raised to the power of the number of bits. In this case, 210 is 1,024. In comparison, an 8-bit system, or 28, has 256 discrete values.


Cable equalization - The method of altering the frequency response of a video amplifier to compensate for high frequency loss in cables that it feeds. Also see "Peaking."

Cable Jacket - The outer protective covering of wire or fiber optic cable.

CAD - Computer Aided Design. The use of the computer system for designing, such as in architectural and engineering applications.

Candela - Derived from the word “candle” and denoted by the symbol “cd”, the candela is the standard unit of light intensity. One candela is roughly equal to the amount of light, in any direction, from the flame of a candle. The luminance of a light source is often expressed in candelas per square meter (cd/m2).

Capacitance - The ability to store an electrical charge.

Capacitor - A device made up of one or more pairs of conductors, separated by insulators and capable of storing an electrical charge. When there is a difference of potential between the conductors, and because current cannot flow through the insulator, an electrical charge is stored.

CAPEX - Capital Expenditure. Expenditures creating future benefits. Incurred when a business spends money either to buy fixed assets or to add to the value of an existing fixed asset with a useful life that extends beyond the taxable year.

Captive screw connector - A connector that uses a screw to hold a stripped wire end.

CAT 5 - Category 5. Describes the network cabling standard that consists of four unshielded twisted pairs of copper wire terminated by RJ-45 connectors. CAT 5 cabling supports data rates up to 100 Mbps. CAT 5 is based on the EIA/TIA 568 Commercial Building Telecommunications Wiring Standard.

CAT 5e - Enhanced Category 5. The standard for the next higher grade of unshielded twisted pair (UTP) beyond Category 5. The CAT 5e specification was developed to provide more robust support for 1000Base-T. CAT 5e specifies tighter limits than CAT 5 for NEXT, ELFEXT, and return loss.

CAT 6 - Category 6. The standard for the next higher grade of unshielded twisted pair (UTP) cabling beyond CAT 5e. The standard defines components (cable and connecting hardware) and cabling (basic link and channel) for Category 6 channels, as well as Level III field tester requirements.

CAT 7 - Category 7. The cable standard for 10 Gigabit Ethernet using shielded twisted pair – STP) cable. Cat 7 features strict guidelines for crosstalk and system noise, requiring shielding for each pair of wires and the cable as a whole.

Cathode Ray Tube - A vacuum tube that produces light when energized by the electron beam generated inside the tube. A CRT has a heated cathode and grids in the neck of the tube, making up the "gun". Electrons are accelerated from the gun toward the front surface of the tube (screen), producing a beam. The surface on the back of the screen is coated with phosphors that light up when struck by the electron beam. The CRT in a TV is known as the picture tube, some of which have three guns - for red, green and blue colors.

CCD - Charge Coupled Devices. A light-detecting circuit array used in video cameras, scanners, and digital still cameras.

CCIR - Comite Consultatif International des Radio-Communications, the International Radio Consultative Committee. The CCIR has been superseded by the International Telecommunications Union, or ITU. Also see "ITU."

CCIR 601 - See "ITU-R BT.601"

CCITT - French term for Consultative Comité of International Telephone and Telegraph, the international group that sets standards for telephony and digital communications (e.g., H.320 — the audio and video codecs and protocol for ISDN).

CCTV - Closed Circuit Television. A distribution system that limits reception of an image to those receivers that are directly connected to the origination point by coaxial cable or microwave link.

CE - Conformité Européenne. A label or mark on a product signifying ESD, EMI, and safety compliance with all European Union (EU) directives applicable to that product. Some interpret it to mean European Community or Compliance for Europe.

CEC – Consumer Electronics Control - A bidirectional serial control bus defined in the HDMI 1.0 specification and subsequent updates. CEC is used to provide control for multiple products, connected via HDMI cables, from a single remote control. Alternately, one device, for example a Blu-ray Disc player, can turn on another device, such as a display, when put into Play mode. CEC command sets are proprietary to each manufacturer; Sony CEC commands cannot control devices from Panasonic or Sharp, and vice versa.

CEDIA - Custom Electronic Design and Installation Association. CEDIA is an international trade association of companies specializing in planning and installing electronic systems for the home. This association offers an annual expo.

CENELEC - European Committee for Electro-technical Standardization.

CET - Carrier Ethernet Transport. Wide-area Ethernet services used for high-speed connectivity within a metropolitan, nationwide, or even internationally.

CGA - Color Graphics Adapter. Introduced in 1983, it was IBM’s first product to display both color and graphics. CGA has a horizontal scan frequency of 15.75 kHz and a vertical frequency of 60 Hz.

Chroma - (chroma signal) (1) Hue and saturation are qualities of chroma. Chroma does not include black, gray, or white. The purity or intensity of color, sometimes called “hue.” Color information, independent of luma intensity or brightness. Without the chroma signal, the video picture would be black and white. (2) The NTSC or PAL video signal contains two parts that make up what you see on the screen: the black and white (luma) part, and the color (chroma) part.

Chroma burst - See "Color burst."

Chroma crawl - An artifact of encoded video also known as dot crawl or cross-luma. It occurs in the video picture around the edges of highly saturated colors as a continuous series of crawling dots (“dancing ants”) and is a result of color information being confused with luma information by the decoder circuits.

Chroma delay - A video problem in which the color of an object or area is shifted slightly to the right of the luma (intensity).

Chroma gain (chroma, color, saturation) - In video, the gain of an amplifier as it pertains to the intensity of colors in the active picture.

Chroma key (color key) - A film and video process in which the subject is filmed in front of a blue or green background (the key color). For example, a weather reporter stands in front of a blue wall with a camera focused on him or her. The camera’s video signal feeds into a chroma keyer, which detects the blue background and replaces it with a video signal from another source, such as video of a weather map. Thus, the reporter appears to be standing in front of the weather map.

Chromatic Dispersion – CD - In fiber optics, a factor that reduces fiber bandwidth as a result of the separation of the incoming light into components of various wavelengths, which travel at different speeds along the fiber. This effect is associated with singlemode fiber at very long distances.

Chromaticity - Is an objective specification of the quality of a color regardless of its luminance, that is, as determined by its hue and colorfulness (or saturation, chroma, intensity, or excitation purity).[1][2]

Chrominance - The measurement of the color value or color difference value in a pixel.

CIE - Commission Internationale de l’Eclairage (the International Commission on Illumination). The international authority on lighting, illumination, color, and color spaces. They have developed many related colorimetry standards and chroma systems in compliment to ITU-R BT.601, which was developed by CCIR and previously known as CCIR 601.

Cladding - In fiber optics, the outer layer surrounding the core of a fiber that serves as an optical barrier as well as protection for the core. The index of refraction for the cladding is always lower than that for the core in order to maintain total internal reflection and thus ensure that the light always travels within the core.

Class A - The output transistor(s) always have current flowing through them. This method of operation is pure, but inefficient. Class A amplifiers rarely exceed 20% efficiency in terms of power consumed (converted to heat) versus power delivered to the load.

Class A/B - A combination of Class A and Class B amplifier designs that corrects the inefficiency of Class A amplifier designs and allows a small amount of current to continually flow through the output transistors at all times. This alleviates most of the cross-over distortion at the expense of efficiency. An A/B amplifier is still more efficient (60 to 65%) than a Class A amplifier.

Class B - Somewhat more efficient than Class A. Class B amplifiers utilizing two drive elements operating in a push-pull configuration. On the positive excursion of the signal, the upper element supplies power to the load while the lower is turned off. During negative going signal excursions, the opposite operation occurs. This increases operating efficiency, but the exchange from ON to OFF causes a switching error condition commonly called cross-over distortion.

Class D - Also known as a switching amplifier, Class D amplifiers utilize output transistors which are either completely turned on or completely turned off (they’re operating in switch mode). Class D amplifiers operate either in the fully ON-region or fully OFF-region. Class D amplifiers reach efficiencies as high as 90%. This is of great importance to portable applications relying on battery power and for the lowest production of heat.

Cleave and Crimp - In fiber optics, the utilization of pre-polished connectors to significantly reduce termination time by eliminating the most time consuming step – polishing the connectors, so that the process requires just cleaving the fiber, insertion into the connector, and crimping.

Cleave Tool - Also known as a scribe tool, this specialized tool is used to break off a portion of an optical fiber by scoring, or scribing the fiber so that it can be cut using a cleaver to ensure a clean, precise, cut with the endface flat and at a 90-degree angle to the fiber axis.

Cleaving - The process of cutting the end of an optical fiber after it has been scored, or scribed using a cleave or scribe tool. The cut is made at a precise 90 degree angle to the fiber axis.

Client - A computer or network device that uses information supplied by a server.

Cliff effect - The sudden or discrete loss of signal at a digital receiver due to the degradation of a transmitted signal that has been terminated due to an error rate being exceeded and the received signal being rejected.

Clipping - Cutting off the peaks (or excursions) of a signal. A form of distortion that occurs when the signal excursions exceed the limits of the circuit.

Clipping level - An electronic limit to avoid overdriving an audio or video signal.

Clock rate - The rate at which analog audio is sampled and converted to a digital signal. Clock rate is important in digital audio recording and processing systems. When samples are not output at the correct time relative to other samples, a condition called “clock jitter” occurs. Clock jitter can also arise when digital audio is run through several audio products. When each product runs on its own clock, compensating for small differences between the clocks can cause output errors. For instance, even if both clocks are at exactly the same frequency, they will almost certainly not be in phase. If the clock rate of the input digital stream and the playback unit differ (44.1 KHz and 48 KHz, for instance), the playback unit has no choice but to perform a sample rate conversion. If they are the same, the playback unit may use sample rate conversion to oversample the input (for example, 88.2 or 96 kHz), then pick the samples that “line up” with its own clock.

CMOS – Complementary metal oxide semiconductor, a chip technology for cameras that is more sensitive to light, produces less heat, and uses less power than CCDs

CMR - Common Mode Rejection. A measure of how well a differential amplifier rejects a signal that appears simultaneously and in phase at both input terminals. As a specification, CMR is expressed as a dB ratio at a given frequency.

CMRR - Common Mode Rejection Ratio. (1) For a differential amplifier, the ratio of the differential gain to the common mode gain. (2) Expressed in dB, it is the ratio of common mode input voltage to output voltage. (3) For an operational amplifier, the ratio of the change in input offset voltage to the change in common mode voltage.

CMYK - Cyan, Magenta, Yellow, and Black. Also see "Subtractive color process."

Coarse Wavelength Division Multiplexing – CWDM - The multiplexing, or combining of several wavelengths into a single optical signal. CWDM is distinguished from Dense Wavelength Division Multiplexing – DWDM in that the separation between wavelengths – 20 nm – is much greater.

Coating - A layer of plastic covering over the fiber to provide protection from moisture as well as damage in manufacturing fiber optic cables. Also known as a buffer coating.

Coaxial cable - A two-conductor wire in which one conductor completely wraps the other, with the two separated by insulation. Constant impedance transmission cable. Example: 75 ohm, type RG-59 cable used for video signals. Abbreviated as coax.

Coaxial speaker - A type of speaker design in which a high frequency driver (typically a tweeter) is placed inside a low or mid frequency driver.

CobraNet - A trademark of Peak Audio, CobraNet is network technology for the transmission of digital audio, video, and control signals over 100Mbps Ethernet networks.

Codec - (1) Coder/decoder. A device that converts analog video and audio signals into a digital format for transmission over telecommunications facilities and also converts received digital signals back into analog format. It may also dial up the connection, like a modem for teleconferencing. (2) Compressor/decompressor. Codecs can be implemented in software, hardware, or a combination of both. Some popular codecs for computer video include MPEG, QuickTime, and Video for Windows.

Collision - Two devices on a network attempt to use the physical media at the same time. The data from the two devices collides.

Color adjustment - A video adjustment that is used to control color or chroma intensity.

Color bars - A standard test pattern of several basic colors (white, yellow, cyan, green, magenta, red, blue, and black) as a reference for system alignment and testing. In NTSC video, the most commonly used color bars are the SMPTE standard color bars. In PAL video, the most commonly used color bars are eight full field bars. In the computer, the most commonly used color bars are two rows of reversed color bars.

Color black - The NTSC standard for black, which is 8% gray. Computer black, the absence of all of the color primaries, is referred to as superblack and is used for matting or keying in video effects. Superblack does not render well to video. Instead of appearing black, it has a light gray appearance. Color black will appear blacker on video than superblack.

Color burst - In color TV systems, a burst of subcarrier frequency located on the back porch of the composite video signal. This serves as a color synchronizing signal to establish a frequency and phase reference for the chroma signal. Color burst is 3.58 MHz for NTSC and 4.43 MHz for PAL.

Color depth - Describes the number of bits used to represent the color of a single pixel in a bitmapped image or video frame buffer. A common bit depth applied to computer graphic signals is 8-bits each for Red, Green and Blue. An 8 bit depth will produce 256 levels and 256 raised to the 3rd power, results in a resolution of over 16 million colors.

Color encoder - A device that combines the separate red, green, and blue signals into one composite video signal.

Color phase - The timing relationship of the color video signal. The correct color phase will produce the correct color hues.

Color Quantization - Color quantization defines the resolution, or number of colors used in a system. This is this is important for displaying images that support a limited number of colors and for efficiently compressing certain kinds of images. For example, reducing the number of colors required to represent a digital image makes it possible to reduce its file size or streaming bit rate.

Color resolution - The number of colors available at one time in an image, measured in terms of bits per pixel.

Color Space - A system for describing color numerically. There are several color space definitions, each used to support the specific identity of colors within a structured identification system. In AV presentation, there are two primary video color space definitions: RGB, which describes the three color primaries, Red, Green, and Blue; and Component or YUV, which describes the luminance channel (Y) and two chrominance channels, U (Blue minus Y) and V (Red minus Y), with the remainder representing Green. RGB is most commonly used with high-resolution computer video signals, while YUV is the primary color space for motion video and television transmission. While the earlier DVI standard supports only RGB, the newer HDMI, and DisplayPort standards support both RGB and YUV color space, and color space conversion is common in sources such as Blu-ray Disc players and both flat panel and projection display devices.

Color space and color space conversion pose a unique challenge when switching between signals with different color spaces, for example, switching a source in YUV color space to a display device set up to receive signals in RGB color space. Many digital displays will automatically detect the change in color space, but may require several seconds or more to lock to the new signal and display it properly. Some displays, on the other hand, require manual intervention to select the new color space through an on-screen display menu.

Color subcarrier - The carrier signal or frequency on which the color signals are modulated. The most commonly used color subcarrier frequency is 3.58 MHz for NTSC, and 4.43 MHz for PAL.

Color temperature - The color quality, expressed in degrees Kelvin (K), of a light source. The higher the color temperature, the bluer the light. The lower the temperature, the redder the light. Benchmark color temperatures for the A/V industry include 5000° K (a comparatively “warm” or reddish color temperature, favored for pleasing video reproduction); 6500° K (D65, the reference color for accurate color reproduction); and 9000° K (a comparatively “cold” or bluish color temperature, favored for graphics and other high-contrast image reproduction).

Comb filter - A filter circuit that passes a series of frequencies and rejects the frequencies in between, producing a frequency response that resembles the teeth of a comb. This is an improvement over the notch filter. Its precise separation of the chroma and luma reduces both cross chroma and cross luma artifacts (chroma crawl or zipper artifacts). It preserves more detail in black and white, resulting in a better quality picture. Although comb filters are successful in reducing artifacts, they may also cause a certain amount of loss of resolution in the picture.

Combing - An undesirable blurring of an image that contains motion. This effect occurs when a single frame of video combines two fields of video derived from different frames of film.

Communication Bandwidths - Below are listed commonly available bandwidths for network switching equipment and connections made available for public and private networks.

All communication bandwidths presented below are listed in Megabits/s (Mb/s). 1,000 Mb/s equals 1 Gigabit/s (Gb/s).

Half-Duplex LAN Switched Fabric (See Note)   Mb/s

Cisco Catalyst 3750                                                 16,000.00

Raptor Networks RAST                                            80,000.00

Cisco Catalyst 6509                                                  140,000.00

LAN Local Connections                                          Mb/s

Ethernet (10 BaseT)                                                   10.00

Fast Ethernet (100 BaseT)                                         100.00

Gigabit Ethernet (1000BaseT)                                   1,000.00

10 Gigabit Ethernet                                                    10,000.00

WAN and MAN                                                           Mb/s

ISDN4                                                                            0.51

DS1/T1                                                                          1.54

DS1C/T-1C                                                                    3.15

DS2/T-2                                                                         6.31

DS3/T3                                                                          44.74

DS3D/T-3D                                                                   135.00

DS4                                                                                274.18

E-1                                                                                 2.05

E-2                                                                                 8.45

E-3                                                                                 34.37

E-4                                                                                 139.26

E-5                                                                                  565.15

OC-1                                                                              51.84

OC-3                                                                             155.52

OC-12                                                                           622.08

OC-24                                                                           1,273.86

OC-48                                                                           2,547.71

OC-192                                                                         10,240.00

OC-256                                                                         13,589.50

OC-768                                                                         40,768.51

Remote Wireless                                                       Mb/s

Satellite Internet                                                          0.51

Broadband Satellite internet                                     2.02

Microwave 4 DS1                                                         6.18

802.11b                                                                         11.00

IPDirect-Sat                                                                   20.00

 155.31g                                                                          54.00

Microwave OC3                                                             155.31

10G Laser                                                                       10,000.00

Please Note from Extron: Full-duplex switched fabric capacity is typically specified by manufacturers. Half-duplex capacity is typically more relevant to multicast video applications as it identifies the one-way sustained throughput directionally. Switched network architecture and intelligent switching features, including hardware or software routing, multicast routing protocol support, latency and other factors can be far more critical to consider than switched fabric capacity when designing switched networks.

Component digital - Digital video using separate color components, such as Y, Cb, Cr. Digital recording formats such as D1 (Sony, BTS/Philips) and D5 (Panasonic) utilize component digital recording technology. Component digital is the digital representation of the component analog signal set, Y, B-Y, R-Y; it is often represented as 4:2:2. The encoding parameters are specified by ITU-R BT.601-2 (formerly known as CCIR 601).

Component video - Color television systems start with three channels of information: red, green, and blue (RGB). In the process of translating these channels to a single composite video signal, they are often first converted to Y, R-Y, and B-Y. Both three-channel systems, RGB and Y, R-Y, B-Y, are component video signals. They are the components that eventually make up the composite video signal. Higher quality program production is possible if the elements are assembled in the component domain.

Composite digital - Digital video that is essentially the digitized waveform of NTSC or PAL video signals, with specific digital values assigned to the sync, blank, and white levels. Commonly described as “4fsc”, a sampling rate locked to four times the frequency of color subcarrier. Early digital tape formats, such as D2 (Sony) and D3 (Panasonic), used a composite digital recording scheme. Also refers to digitally encoded video signal, such as NTSC or PAL video, that includes horizontal and vertical synchronizing information.

Composite sync - A signal combining horizontal and vertical sync pulses and equalizing pulses with no picture information and no signal reference level. Composite sync is sometimes referred to as “C”, “S” (as in RGBS), or “HV” (as on some connector panels).

Composite video - An all-in-one video signal comprised of the luma (black and white), chroma (color), blanking pulses, sync pulses, and color burst.

Compression - The art and science of reducing the amount of data required to represent a picture or a stream of pictures and sound before sending or storing it. Compression systems are designed to eliminate redundant or repeated information to the desired data level while allowing the original information to be reproduced to the desired quality.

Compression (Audio) - Compression is commonly used to keep mic levels within an acceptable range for maximum intelligibility. Though a compressor effectively makes louder portions of a signal softer, it is used to make softer sounds louder. This is achieved by reducing the dynamic range, then raising the output level of the compressor (referred to as "make-up gain"), or by increasing the input signal, then preventing clipping by reducing the louder portions of the signal. Compression is also used to protect a system or a signal chain from overload.

Compression artifacts - Compacting of a digital signal, particularly when a high compression ratio is used, may result in small errors when the signal is decompressed. These errors are known as artifacts, or unwanted defects. The artifacts may resemble noise (or edge busyness) or may cause parts of the picture, particularly fast moving portions, to be displayed as distorted or incomplete.

Compression connector - A special connector, such as a BNC, RCA, or F-Connector, that is quickly and securely attached to a cable by using a compression tool. The connector is compressed onto the cable. Also see "Compression tool."

Compression tool - A special cable tool that is used to quickly and securely attach a connector, such as a BNC, RCA, or F-Connector, by compressing the connector to the cable. Also see "Compression connector."

Compressor - A compressor regulates the level of an input signal by reducing or compressing its dynamic range above a user-defined threshold. Also see "Compression (Audio)."

Computer-video interface - A device that converts the nonstandard video output of computer systems to a standard RGB analog signal, which can then be connected to a compatible data monitor and projector.

Congestion - Occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queueing delay, packet loss or the blocking of new connections. A consequence of this is that increases in offered load lead to only small increases in network throughput, or to an actual reduction in network throughput.

Constant Bit Rate (CBR) - Constant bit rate encoding means that the rate at which a codec’s output data should be consumed is constant. CBR is useful for streaming multimedia content on data communication channels which operate more efficiently or require the bit rate to remain within a tight tolerance. Typically the constant bit rate is created by stuffing bits into a variable bitrate signal which has a defined peak or maximum limit.

Constant Quality - The quality output from a process, such as video encoding remains constant, while the output, such as a bit rate may vary. Constant quality encoding will result in a variable bit rate if the nature of the video material changes.

Constant voltage system - The common name given to the interface between amplifiers and speakers in a distributed audio system. Several voltages are used, but the most common are 70.7 V (commonly shortened to 70 V) in the US, and 100 V in Europe. “Constant voltage” refers to the characteristic that whether the total output of the amplifier is 5 watts or 50 watts or 500 watts, the maximum output voltage is always a constant of 70.7 V. The voltage stays the same regardless of the load, so the output current varies but not the voltage.

Contact closure - The momentary connection of two conductors to complete an electrical circuit. Often used to switch inputs on switchers.

Contention - The media that network devices use to deliver data is overused and “contention” for the media is experienced.

Continuity - In digital picture manipulators, the characteristic of location/positioning that determines if the motion path continues smoothly.

Continuous power - The continuous power specification can be used to describe the output of an amplifier and is typically stated at “x watts (rms) into y ohms from 20 Hz to 20K Hz at z% THD (total harmonic distortion)”. For example, the Extron MPA 122 amplifier is specified as 11 watts (rms) per channel into 4 ohms at 1% THD.

Continuous presence - A feature in some videoconferencing equipment that allows the participants to view multiple sites on the same video screen. This is a function of the codec used and not of the video switching system.

Contouring - Digital video picture defect caused by quantizing at too coarse a level.

Contrast - The range of light and dark values in a picture, or the ratio between the maximum and the minimum brightness values. Low contrast is shown mainly as shades of gray, while high contrast is shown as blacks and whites with very little gray. It is also the name of a TV monitor adjustment, which increases or decreases the level of contrast of a displayed picture. Also called “white level.”

Contrast range - The range of grays in a video image.

Contrast ratio - The ratio of the high light output level divided by the low light output level. In theory, the contrast ratio of the television system should be at least 100:1, if not 300:1. In reality, there are several limitations. In the CRT, light from adjacent elements contaminates the area of each element. Room ambient light will contaminate the light emitted from the CRT. Well-controlled viewing conditions should yield a practical contrast ratio of 30:1 to 50:1.

Convergence - The alignment of the red, green, and blue video projected onto a screen when the lines produced by the three color sources appear to form one clearly focused white line. The point at which the light from each of the three lenses aligns so the perceived single image is clearly focused. Lack of convergence is a video problem when the displayed image appears to be outlined by red, green, or blue because of misaligned colors.

COP-3 - A Code of Practices established by the MPEG Forum for the transmission of MPEG-2 transport streams which applies a technique known as Forward Error Correction to protect the enclosed data.

COP-4 - A Code of Practices for the transmission of uncompressed standard video at up to 270 Mbps and High Definition video at up to 1.485 Gbps which applies a technique known as Forward Error Correction to protect the enclosed data.

Core - The central core of an optical fiber in which the light travels. The core’s index of refraction is always greater than that of the cladding which surrounds it, to maintain total internal reflection and therefore keep the light within the core.

CoS - Class of Service: Method of classifying traffic on a packet-by-packet basis using information in the type-of-service (ToS) byte to provide different service levels to different traffic. See also QoS.

Coupling Loss - The loss of optical power as light passes through a junction, expressed as the ratio of the optical power measured at the junction, such as a coupler, to the total optical power entering the system.

CRC - Cyclic redundancy check, CRC or polynomial code checksum is a method used to detect changes or errors in raw data, and is commonly used in digital networks, data communications and storage devices.

Crest factor - The ratio of peak value of a signal divided by the rms value of the signal. The crest factor of the audio program determines the required headroom needed in the audio system.

Critical Angle - An important angle of incidence for light as it meets a boundary between two refractive materials. Below this angle, total internal reflection occurs. In an optical fiber, light always strikes off the boundary between the core and cladding below the critical angle so that it is internally reflected within the core as it travels along the fiber.

Cross color - Moiré or rainbow artifacts in an encoded video picture caused when the video encoder or decoder misinterprets luma detail as color information, resulting in color being displayed where it shouldn’t be. It is especially noticeable when the subject wears pinstriped clothing.

Cross luma - Dot crawl, chroma crawl. A video artifact that occurs when a composite video decoder incorrectly interprets chroma information (color) to be high-frequency luma information (brightness). This may appear as tiny, colored dots that creep along the edges of objects.

Crosshatch - A test pattern consisting of vertical and horizontal lines used for converging a color display device.

Crossover distortion - A type of distortion that occurs in push-pull class AB or class B amplifiers. It happens during the time that one side of the output stage shuts off, and the other turns on.

Crossover network - An electrical circuit that combines high pass, low pass, and bandpass filters to divide the audio frequency spectrum, 20 to 20,000 Hz, into ranges suitable for low frequencies (woofer), mid-range, and high frequencies (tweeters).

Crosspoint - An electronic switch, usually part of an array of switches that allows video or audio to pass when the switch is closed.

Crosstalk - Caused by interference between two signals, usually from an adjacent channel, which adds an undesired signal to the desired signal. Crosstalk is caused by magnetic induction or capacitive coupling, and can occur when there is a grounding problem or improper cable shielding. Video symptoms include noise and ghosting, while audio symptoms include signal leakage.

CRT - Cathode Ray Tube. A vacuum tube that produces light when energized by the electron beam generated inside the tube. A CRT has a heated cathode and grids in the neck of the tube, making up the gun. Electrons are accelerated from the gun toward the front surface of the tube (screen), producing a beam. The surface on the back of the screen is coated with phosphors that light up when struck by the electron beam. The CRT in a TV is known as the picture tube. Some CRTs have three guns—for red, green, and blue colors.

CSMA/CD - Carrier Sense Multiple Access/Collision Detection. The Media Access Control method applied in Ethernet networks. When a device wants to gain access to the network, it checks to see if the network is quiet (senses the carrier). If it is not, it waits a random amount of time before retrying. If the network is quiet and two devices access the line at exactly the same time, their signals collide. When the collision is detected, they both back off and each waits a random amount of time before retrying.

CTS - Certified Technology Specialist. An A/V and video professional who, through practical experience and extensive industry training programs offered by ICIA, has developed a high level of expertise.

Curing Oven - A specialized oven used to thermally cure epoxy for adhering a fiber optic connector ferrule onto the optical fiber.

Current - The flow of electricity, and the rate at which it flows. Also see "Amp."

Cut - An instantaneous transition between two sources. An instantaneous scene change.

Cutoff Wavelength - In singlemode optical fiber applications, the wavelength below which the fiber transmits as multimode instead of singlemode.


D connector - A connector with rounded corners and angled ends, taking on the shape of the letter D. Commonly used in computers and video, most D connectors have two rows of pins. If they have more than two rows, they are usually called HD (High Density) connectors.

D/A - Digital to analog.

D1 - A component digital recording format that conforms to the ITU-R BT.601 standard, using 19mm tape, uncompressed. Though largely obsolete as a digital recording format, “D1” is commonly used to describe component digital video utilizing a 4:2:2 (Y Cb Cr) signal structure.

D5 - A component digital videotape recording format that conforms to ITU-R BT.601 standard, using 1/2” tape, 10 bits video coding, uncompressed. The primary manufacturer is Panasonic.

D9 - A component digital videotape recording format that conforms to ITU-R BT.601 standard, using 1/2” tape, eight bits, 3:1 compressed. Previously called Digital-S. The primary manufacturer is JVC.

DA - Distribution amplifier. A device that allows connection of one input source to multiple, isolated (buffered) output destinations such as monitors or projectors.

DAC - Digital to analog converter.

Damping factor - The measurement of a power amplifier’s ability to control the motion of a speaker’s cone after a signal disappears. The higher the number, the better the damping factor.

DAR - Data at Rest. All data in storage excluding data that frequently traverses the network or resides in temporary memory.

Dark Fiber - A term in fiber optics to denote fiber that is installed at a facility but reserved for future use.

DAT - Digital Audio Tape. A method developed by Sony and Hewlett-Packard for recording large amounts of information in digital form on a small cassette tape.

Data - (1) A representation of facts, concepts, or instructions in a format suitable for communication, interpretation, or processing by human or automated means. (2) Any representations, such as characters or analog quantities, that have meaning.

Data Compression - A mathematical algorithm for compressing or encoding data to fit within given bandwidth requirements for transmission or storage.

Data Compression Ratio - The ratio representing the data output from a compression system relative to the original data. A computer-science term used to quantify the reduction in data-representation size produced by a data compression algorithm.

Data Link - A fiber optic system comprising the cable, transmitter, and receiver for transmission of data between two locations.

Data Services - A telecommunications service that transmits high-speed data rather than voice. Internet access is the most common data service, which may be provided by the telephone and cable companies as well as cellular carriers.

dB (Decibel) - The standard unit used to express gain or loss of power between two values. A decibel is 10 times the logarithm of a ratio of two power values. When comparing voltage or pressure, the values in the ratio are squared or the log is multiplied by 20 instead of 10. An extension is placed behind the ‘dB’ when one of those values is a fixed reference (i.e. dBV, dBu, dBSPL).

dB per octave - How quickly a crossover or filter attenuates signals (decreases their power) outside its passband (those frequencies intended to pass through without attenuation); expressed in decibels per octave. Crossover and filter slopes are designed as first order (attenuates signals slowly, cutting output by 6 dB per octave); second order (12 dB per octave); third order (18 dB per octave); and fourth order (24 dB per octave). The steeper the slope the quicker the attenuation.

dBm - dB referenced to 1 milliwatt. To convert into an equivalent voltage level, the impedance must be specified. For example, 0 dBm into 600 ohms gives an equivalent voltage level of 0.775V, or 0 dBu; however, 0 dBm into 50 ohms, for instance yields an equivalent voltage of 0.24 V. Since modern audio engineering is concerned with voltage levels, as opposed to power levels in the early years of telephone, the convention of using a reference level of 0 dBm is academic. But in the A/V industry, many people still refer to 0.775Vrms (600 r) as 0 dBm, which should be more accurately called 0dBu.

dBSPL - dB referenced 20 micro pascals (0.00002 PA). 0dBSPL is a scale used to express acoustic energy, that is as loud as sound is. For example, when a sound is described as being “110 dB,” the measurement is expressing the sound pressure level of the source. Benchmarks include: 30-40 dBSPL - ambient room noise; 50-70 dBSPL - normal conversation; 110-120 dBSPL - rock concert; 130-140 dBSPL - painful sound.

dBu - dB unterminated. 0 dBu is a voltage reference point equal to 0.775Vrms. [This reference originally was labeled dBv (lower case) but was too often confused with dBV (upper case), so it was changed to dBu (for unterminated).] +4 dBu is a standard pro audio voltage reference level equal to 1.23Vrms. XLR and captive screw audio connectors are commonly used in this equipment.

dBV - dB referenced to 1.0 Vrms. -10dBV is a standard audio line level for consumer and some professional audio use, equal to 0.316 Vrms. RCA audio connectors are a good indicator of units operating at -10 dBV levels.

DC - Direct Current. The flow of electrons in one direction.

DC coupled - A circuit that passes both AC and DC components of a signal, and therefore is sensitive to DC offsets. Also see "AC coupled."

DC offset - Refers to the degree to which a DC voltage is skewed away from a zero or baseline value.

DC restoration - The correct blanking level for a video signal is zero volts. When a video signal is AC-coupled between stages, it loses its DC reference. A DC restoration circuit clamps the blanking at a fixed level. If set properly, this level is zero volts.

DCF - Dispersion Compensating Fiber

DDC - Display Data Channel. A bi-directional communications standard developed by VESA (Video Electronics Standards Association) that defines a universal data transmission standard for the connectivity between display devices and computers.

DDSP™ - Digital Display Sync Processing™. A signal handling method, trademarked by Extron, that allows the sync signal to pass through without altering sync pulse timing or width. DDSP disables other sync processing features such as horizontal and vertical centering.

DDWG - Digital Display Working Group. The DDWG develops standards for digital displays. Developer of the DVI standard.

Dead Zone - A region within a fiber optic system where an OTDR – Optical Time Domain Reflectometer cannot effectively make measurements.

Decoder - 1) In analog video, a device used to separate the RGBS (red, green, blue and sync) signals from a composite video signal. Also known as an NTSC decoder. 2) In digital systems, a device which does the reverse of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode. Video over IP decoders accept IP data streams and output an analog or digital video signal. 3) In control systems, the device in a synchronizer or programmer which reads the encoded signal and turns it into a form of control.

Deep Color - A very wide color gamut with a bit depth of 30 bits or more, capable of displaying billions of colors.

Default gateway - The routing device used to forward all traffic that is not addressed to a station within the local subnet.

Definition - The fidelity with which a video picture is reproduced. The clearer the picture, the higher the definition. Definition is influenced by resolution.

Degausser - A device that produces a strong alternating electromagnetic field which quickly erases an entire reel, cassette, or cartridge of tape. Also used for eliminating ghosting in television monitors by demagnetizing the CRT.

De-interlacing - The process of combining pairs of interlaced fields of video into one progressive frame of video.

Delay - A basic DSP process in which the output of the input signal is delayed by a specified time (called the delay time).

Dense Wavelength Division Multiplexing – DWDM - The multiplexing, or combining of several wavelengths into a single optical signal. DWDM is distinguished from Coarse Wavelength Division Multiplexing–CWDM in that the separation between wavelengths – 0.8 to 1.6 nm – is much smaller.

Detail enhancement -

Detector - A device within fiber optic receivers that converts optical energy to electrical energy.

DHCP - Dynamic Host Configuration Protocol. A standardized client-server IP networking protocol that enables network administrators to centrally and automatically manage the assignment of IP addresses in an organization’s network.

Dichroic - A type of mirror, reflector, or filter that selectively reflects different wavelengths of light, permitting a projector to transmit more visible light with less heating of the film. Dichroic mirrors are also used for internal convergence of three-tube single lens video or computer projectors.

Dielectric - Insulating material in coaxial cables between center conductor and outer conductor.

Differential audio - See "Balanced audio."

Differential gain - Unwanted variations in a chrominance subcarrier’s amplitude that result from changes in the signal’s DC level, usually specified between 10% and 90% of full scale .

Differential Mode Delay – DMD - A limiting factor in the performance of transmissions over multimode fiber, in which there is a differential in the arrival times at the receiver of various wavelengths, or modes along the fiber. This differential is caused by model dispersion which is inherent in multimode fiber.

Differential phase - Unwanted variations in a subcarrier’s phase as a result of changes in the chrominance signal’s DC level, usually specified in degrees over a frequency range.

Digital - A system of data or image values in the form of discrete, non-continuous codes, such as binary. When data is in a digital format, it can be processed, stored (recorded), and reproduced easily while maintaining its original integrity.

Digital Betacam® - A component digital videotape recording format that conforms to CCIR 601 standard, using 1/2" tape, 10 bits, 2:1 compressed. The primary manufacturer is Sony.

Digital component video - See "Component digital."

Digital composite video - “See Composite Digital.” Also see "Composite digital."

Digital control - A method using discrete digital impulses to control individual functions within a system.

Digital signal - An electrical signal which possesses two distinct states (on/off, positive/negative); typically represented by “0” or “1”.

Digitization - The transformation of an analog signal into digital information.

Digitizers - Video digitizers utilize video cameras to take pictures of photographs or live and still action. The information is decoded into RGB (digital form) and stored in the frame buffer.

D-ILA™ - Direct Drive Image Light Amplifier. The D-ILA is a device based on the Image Light Amplifier or ILA developed by Hughes-JVC Technology Corporation. The D-ILA technology is a reflective liquid crystal modulator whereby electronic signals are addressed directly to the device. The D-ILA device has an X-Y matrix of pixels configured on a C-MOS single crystal silicon substrate mounted behind the liquid crystal layer using a planar process that is standard in Integrated Circuit technology.

DIM - Data in Motion. Data that is actively moving from one location to another, such as across the Internet or through a private network.

DIN connector - An acronym for Deutsche Industrie Norm. A round connector with notches, or keys, for alignment. They exist in several sizes: 4 pins, 5 pins, 8 pins, etc. A convenient way of combining all of the signal lines in one connector, 4-pin DIN connectors are often used for S-video.

Diode - An electronic device that allows current to flow in one direction only.

DIP - Dual In-line Package. A universal method of manufacturing integrated circuits (ICs) with the pins arranged in two parallel rows. Some DIP components are soldered in and some use DIP sockets.

DIP switches - Small switches that are used to change settings on printers, computers, interfaces, switchers, modems, etc. They are designed to fit in a DIP (Dual Inline Package) space on a circuit board.

Direct View LED - (dvLED's) are seamless, bezel free, LED panels that vary in pixel pitch configurations and can adapt to practically any indoor or outdoor environment. The dvLED pixel is the smallest element of a picture creating a single point of color.

Discrete Cosine Transform (DCT) - A Fourier-related transform which is used to convert an image from a spatial domain to a frequency domain. Video systems then process the information in the frequency domain. Typically, more signal energy is located in the lower frequencies than the higher frequencies. The DCT is used in many video compression codecs including JPEG, MPEG, MPEG-2, MPEG-4 and H.264.

Discrete Wavelet Transform (DWT) - A transform used to convert an image from a spatial domain a wavelet domain. Two filters are involved, the first a “wavelet filter” is a high pass filter, and the second a “scaling filter” a low pass filter. The DWT provides more efficient image compression than the DCT as it due to advantages analyzing signals with sharp discontinuities or spikes.

Dispersion - A limiting factor in optical fiber transmission performance, where a light pulse is broadened, or separated into modes or individual wavelengths. Dispersion limits transmission bandwidth and distance capability. The two major types of dispersion are modal dispersion and chromatic dispersion.

Dispersion Compensating Fiber – DCF - A special type of fiber designed to exhibit a large negative dispersion. DCF is typically used in long-haul telecommunication systems to compensate for dispersion in optical fiber.

Dispersion Shifted Fiber – DSF - A singlemode optical fiber with its optimal dispersion wavelength shifted, through the addition of dopants, to a wavelength that delivers optimal attenuation.

Display device - Any output device for presenting information visually. Examples include: CRT (Cathode Ray Tube), LED (Light Emitting Diode), or LCD panel (Liquid Crystal Display). A general term for a projector or monitor.

DisplayID - Released in December 2007, this second-generation version of VESA EDID – Extended Display Identification Data is intended to replace all previous versions. DisplayID represents a 256-byte data structure that conveys display-related information to attached source devices. It is meant to encompass PC display devices, consumer televisions, and embedded displays such as LCD screens within a laptop without need for multiple extension blocks. Display ID is not directly backward compatible with previous EDID/E-EDID versions.

DisplayPort - The newest digital audio/video interconnect standard, designed primarily for use between a computer and display device. DisplayPort supports data rates up to 10.8 Gbps at a distance of 2 meters for full bandwidth transmissions, and up to 15 meters for reduced bandwidth signals such as 1080p/60, over copper cable. DisplayPort is not directly compatible with DVI or HDMI, but a DisplayPort connector can pass these signals, and the standard does provide an emulation mode for ease of integration with DVI or HDMI equipped products.

Dissolve - (1) An effect in which one scene or picture fades out as another fades in. In projection, the dissolve effect is achieved by varying the intensity of the lamps in the two projectors involved. Sometimes called lap dissolve or cross fade. (2) The hardware controlling the dissolve effect, which is properly called dissolve control or dissolve unit. A visual effect wherein one scene gradually fades away while slowly being replaced by another. Also see "Fade, Fade-to-black."

Distribution amplifier - A device that distributes multiple outputs from a single source input. Distribution Amplifiers (DAs) split signals, but also provide amplification and enhancement features to maintain the integrity of the signals.

Distribution Cable - Fiber optic cable comprising a bundle of jacketed fibers encased within an outside jacket.

Distribution Panel - For fiber optic applications, this is both a patch panel and splice panel, usually installed at a hub or entrance facility

Dither - (1) The process of filling a gap between two pixels with another pixel having an average value of the two to minimize the difference or add detail to smooth the result. (2) In audio, a process that deliberately adds a tiny amount of noise to a signal in order to mask unwanted sounds introduced when the signal’s original bit depth is reduced. Dithering is recommended when transferring audio to a device that uses a lower bit depth.

DLP™ - Digital Light Processing. An imaging technology for video projection developed by Texas Instruments, based on the modulation of light reflected from mirror elements known as Micromirrors(tm). Each pixel is represented by its own Micromirror, which mechanically tilts in accordance to the extent of light reflected toward or away from the screen. A matrix of Micromirrors comprising the video image is situated on a microchip, or DMD(tm) (Digital Micromirror Device). DLP is implemented as a three-chip configuration (one DMD for each of the RGB colors), or as a one-chip configuration (R, G, and B are sequentially processed by a single DMD via a color wheel).

DMI™ - Dynamic Motion Interpolation™. This Extron video processing technique is an advanced motion prediction and compensation method that treats motion content and still content with different algorithms to yield high fidelity images.

DMM - Digital Multimeter. A test and measurement device, typically handheld, that combines measurement tools for voltage, amperage, resistance, and other common electrical and electronic measurement needs.

DNS - Domain Name System. DNS is the way that an Internet domain name is located and translated into Internet Protocol (IP) addresses. A domain name is a meaningful and easy-to-remember “handle” for an Internet address.

DOC - Declaration of Conformity. A document that states the European Union directives and standards to which particular equipment should comply.

Dolby noise reduction - A patented noise reduction technique from Dolby Labs that raises the volume of sound track elements most likely to be affected by inherent noise during recording and then lowers them again during playback so that the noise seems lower in relation to the wanted elements of the audio recording.

Dolby® Digital - A digital audio encoding and decoding technology utilized for DVDs, Blu-ray Discs, video games, and many cable and satellite television services. Also referred to as “AC-3.” Dolby Digital can transmit mono or standard two-channel stereo audio, as well as 5.1 channel surround sound (left front, center front, right front, left rear, right rear, and sub-woofer).

Dolby® Digital Plus - A digital audio compression technology designed as an optional codec for use with Blu-ray Disc. Dolby Digital Plus is an extension of the earlier Dolby Digital format and supports up to 13 audio channels, although Blu-ray Disc is limited to 8 discrete channels. The extra audio channels are often used to support multiple languages.

Dolby® TrueHD - An advanced, lossless multi-channel audio encoder and decoder technology intended primarily for high-definition content and is optional for Blu-ray Disc; support for TrueHD is also optional in the HDMI 1.3 specification. TrueHD supports up to 8 discrete audio channels at 96 kHz sampling, or up to 6 channels at 192 kHz sampling. Since TrueHD is optional for Blu-ray Disc, discs encoded with a TrueHD audio track must also include a separate 2-channel digital audio track.

Domain - When referring to the Internet, a name that identifies a network. (i.e.

Domain Name System (DNS) - The Internet’s equivalent of a phonebook containing a directory of domain names and translating them to Internet Protocol (IP) addresses.

Dot clock - Also referred to as pixel clock. The timing device in a graphics card that determines the pixel resolution. The dot clock runs at a rate that produces the highest possible pixel resolution for that device. In a digital projector, the dot clock samples the analog video at a rate that produces the resultant pixel resolution. Also see "Pixel clock."

Dot crawl - Sometimes called “zipper effect,” dot crawl refers to a specific image artifact that is a result of the composite video system. Dot crawl may be seen on TV news, for example, when a picture appears over the anchorperson’s shoulder, or when some text appears on top of the video clip. If you look closely, along the edges of the picture, or the text that has been overlaid, you’ll notice some jaggies rolling up or down.

Dot pitch - The vertical distance (measured in millimeters) between the centers of like-colored phosphors that are in adjacent pixels on the monitor screen. The closer the spacing, the better the resolution. Dot pitch is specified in pixels/mm.

DPCP – DisplayPort Content Protection - DPCP is a content-protection scheme for DisplayPort developed by Advanced Micro Devices. Like HDCP 2.0, DPCP uses AES 128 encryption. To date, DPCP has not been implemented by any manufacturer of source or display devices equipped with DisplayPort. All devices currently on the market use HDCP for digital rights management.

Drain wire - Non-insulated wire used in cable termination as a ground connection.

DRM – Digital Rights Management - A generic term for technologies such as content scrambling in cable or satellite television transmission, HDCP, and DPCP that can be used to control the access to, or reproduction of, copyrighted, commercially-available content. DRM is used primarily to prevent piracy, the unauthorized duplication and distribution of copyrighted material. However, DRM often also governs how content can be used. Commercially-available DVDs and Blu-ray Discs, for example, are typically licensed for personal use in a residential environment. Use of such content in a public venue, such as a school or business setting, without express consent or licensing by the copyright holder, is typically in violation of the media’s license.

Dry contact closure - A pair of electrical contacts that carry no live voltage.

DSL - Digital Subscriber Line. A generic name for a family of digital lines (also called xDSL) provided by telephone carriers to business and consumers.

DSP - Digital Signal Processor. A specialized CPU or circuit designed to process signals such as audio and video which have been converted to digital form. DSP is used to process sound, video, and images in a variety of ways.

DSS - Digital Satellite System.

DSVP™ - Digital Sync Validation Processing™. In critical environments or unmanned, remote locations, it is vital to know that sources are active and switching. Extron's exclusive DSVP technology confirms that input sources are active by scanning all sync inputs for active signals. DSVP provides instantaneous frequency feedback for composite sync or separate horizontal and vertical sync signals via the switcher's RS-232/422 port.

DTS® Digital Surround - A digital audio encoding and decoding technology from DTS, Inc. that delivers 5.1 channels of surround sound. It is an optional surround sound format for DVDs but is mandatory for Blu-ray Disc. DTS Digital Surround has also been used in some LaserDisc releases as well as CDs, and is also featured in some video games.

DTS-HD High Resolution Audio - An extension to the DTS Digital Surround format that offers up to 7.1 channels at 24-bit resolution and 96 kHz sampling. DTS-HD High Resolution Audio is an optional surround sound format for Blu-ray Disc.

DTS-HD Master Audio - A lossless audio encoder/decoder technology from DTS, Inc. DTS-HD Master Audio allows a bit-for-bit representation of a movie’s original studio master soundtrack and supports up to 8 audio channels. Support for DTS-HD Master Audio is optional in the HDMI 1.3 specification released in 2006, and is also optional for Blu-ray Disc.

DTV - Digital Television. Often used to describe one of the many new forms of digital terrestrial transmission of video program material.

Dual-Link DVI - A dual-link DVI output has two TMDS links and twice the bandwidth of single-link DVI, and can therefore support much higher resolutions. With two TMDS links, the number of data channels is doubled, although there is still only one clock signal, so both links are clocked identically. Apples 30 Cinema Display with a native resolution of 2560x1600, is an example of a display requiring dual-link DVI. See also Single-Link DVI. Also see "Single-Link DVI."

Dual-Link HD-SDI - Is a method applying two HDSDI signals 1920x1080 video at 50 or 60Hz as progressive frames, at 12 bit depth or with 4:4:4 color quantization.

Duplex - Data transmission in both directions. Half duplex denotes transmission in one direction at a time, while full duplex refers to simultaneous transmission in both directions. In fiber optics, duplex also refers to a type of cable comprising two fibers for duplex transmission.

Dust Cap - A plastic cap that covers the connector ferrule, plug, or sleeve, and protects the connector endface.

DV - Digital Video. A serial digital video format. DV has the advantage over standard analog video of maintaining clear, crisp video without degradation from generation to generation.

DVB/ASI – Digital Video Broadcasting/Asynchronous Serial Interface - A standard for the broadcast of digital television signals. Terrestrial broadcast, primarily seen in Europe, is often stated as DVB-T. In the US, DVB-S is often used for compression and encoding of digital satellite transmission; for terrestrial applications, North America utilizes the ATSC standard.

DVD - Digital Versatile Disc. An optical disc similar in physical size to a CD-ROM, but capable of storing an entire movie. The technology uses MPEG-2 compression. Typical capacity for these discs is 4.5 GB, or about 133 minutes of digital video.

DVD-Audio - A digital format for delivering high-fidelity audio content on DVD – Digital Video Discs. DVD-Audio is a standalone format intended for audio only and is not used for the audio portion of DVD video content. DVD-Audio is similar in application to SACD, although to maintain compatibility with DVD players, the format is not capable of the very high sampling rates found in SACD. Support for DVD-Audio was added to the HDMI 1.1 specification in 2004.

D-VHS - Digital-VHS. A new technology based on VHS, offering the features of conventional VHS with bit stream recording capability which allows the recording and playback of compressed digital data including digital television broadcasts and prerecorded high definition software.

DVI - Digital Visual Interface. The digital video connectivity standard that was developed by the DDWG – Digital Display Working Group. This connection standard offers two different connectors: one with 24 pins that handles digital video signals only and one with 29 pins that handles both digital and analog video. This standard uses TMDS – Transition Minimized Differential Signal from Silicon Image and DDC – display Data Channel from VESA – Video Electronics Standards Association.

DVI-D - DVI connector that supports digital signals only.

DVI-I - DVI connector that supports both digital and analog signals.

dvLED - Direct View LED’s are seamless, bezel free, LED panels that vary in pixel pitch configurations and can adapt to practically any indoor or outdoor environment. The dvLED pixel is the smallest element of a picture creating a single point of color.

Dynamic IP address - An IP address that is automatically assigned to a client host in a TCP/IP network, typically by a DHCP server. Network devices that serve multiple users, such as servers and printers, are usually assigned static (unchanging) IP addresses.

Dynamic range - The highest and lowest potential signal levels on a given device. Also applies to fiber optic applications in terms of the ratio between the most – or strongest – and least – or weakest – observable optical signals.

Dynamic transducer - Technical description of a loudspeaker or dynamic microphone. A dynamic transducer uses a paper, plastic, fabric, or metal cone which is driven by a voice coil that moves back and forth through a magnetic field produced by the audio signal.


EAP - Extensible Authentication Protocol. It is an authentication framework that is often used in network and Internet connections. There are various EAP authentication methods available, and 802.1X uses EAP as part of its authentication process.

Echo cancellation - A DSP technique that filters unwanted signals caused by echoes from the main audio source.

Echo suppression - Used in telephone networks to reduce the impact of echo and thereby improve voice quality. The impact of echo suppression is usually to limit data transmission to one direction at a time. In order to provide for duplex operation, modems request telephone systems to turn off echo suppression.

ECL - Emitter Coupled Logic. A family of high speed, low power IC logic devices. Also called “current mode logic.”

Edge-to-edge - Describes common density factors in loudspeaker layout designs. Edge-to-edge density places the speakers such that the outside edges of their sound cones just touch one another.

EDID - Extended Display Identification Data - EDID is a data structure used to communicate video display information, including native resolution and vertical interval refresh rate requirements, to a source device. The source device will then output the optimal video format for the display based on the provided EDID data, ensuring proper video image quality. This communication takes place over the DDC – Display Data Channel.

EDID Minder® - A proprietary EDID management process from Extron. EDID Minder® automatically manages the EDID information between a digital display device and one or more input sources. By maintaining continuous EDID communication with all sources, EDID Minder® ensures that digital sources power up properly and maintain their video output, whether or not they are actively connected to the digital display device.

EDTV - Enhanced Definition Television. A new digital TV product category added between High Definition TV (HDTV) and Standard Definition TV (SDTV), with the following attributes: a receiver that accepts ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format with active vertical scanning lines of 480 progressive (480p) or higher; no aspect ratio specified; and receives and reproduces, and/or outputs Dolby Digital audio.

EEPROM - Electrically Erasable Programmable Read-Only Memory. The information in an EEPROM is erased by exposing it to an electrical charge. Similar to EPROM except in the way in which information is erased. Also see "Flash memory."

Effective modal bandwidth – EMB - In fiber optics, the modal bandwidth of a multimode fiber when using a laser as a light source. EMB is sometimes referred to as laser launch bandwidth.

EGA - Enhanced Graphics Adapter. Introduced by IBM in 1984, this replaced CGA (Color Graphics Adapter).

EIA - Electronics Industries Association. The association that determines recommended audio and video standards in the US.

EIA sync - The standard broadcast sync, also called EIA-RS-170.

EIA-RS-170 - The standard broadcast sync as determined by the Electronics Industries Association. Commonly called EIA sync.

Electrode - In a fusion splicer, the component which discharges electricity to enable two optical fibers to be fused or welded together.

Electron gun - The part in the CRT that produces the electron beam attracted to the phosphor-coated back surface of the screen. The beam strikes the phosphors, causing them to emit red, green, or blue light, creating images on the screen.

Electrostatic focus - Also referred to as electrostatic deflection. A CRT tube focusing method that uses electrically charged plates instead of deflection coils to focus the electron beam. This method was used only on small CRTs because the larger the CRT, the higher the voltage required, which can cause harmful x-rays to be emitted.

ELFEXT - Equal Level Far End Crosstalk. The amount of crosstalk at the far end after compensation for attenuation over a run.

Embedded data - Digital technologies such as SDI, HD-SDI, and HDMI, can carry variety of other data along with the primary video data, including audio, control, metadata such as content title or other identifying information, or other ancillary information. These data are said to be embedded, as they travel with the primary signal from the source device to the destination.

EMI - Electromagnetic Interference. Any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics/electrical equipment.

Encoder - 1) In analog video, a device, often built into video cameras, that changes individual component signals into composite signals. For example, an encoder combines Y (luma) and C (chroma) signals to produce a video image. 2) In digital systems, A device, circuit, or algorithm that converts information from one format to another. Video over IP encoders take analog or digital video input signals and convert them to IP data streams which are transmitted over IP networks.

Encoding - In video, the combination of electronic elements into one signal; for example, S-video is encoded (combined) to create a composite video signal.

Encryption - To manipulate information into a coded form that cannot be read without a device that will unscramble the code. Video signals are also scrambled in cable and pay-TV systems so that the viewer must pay to receive the program after it has been electronically deciphered.

End Finish - The endface of an optical fiber at the ferrule, finished or polished to be smooth in order to minimize signal loss or backreflection. PC, SPC, UPC, and APC polishing finishes are available for singlemode connectors.

Entrance Facility - In fiber optic applications, the entrance to a building for fiber optic cables.

Epoxy - An adhesive that bonds between surfaces by means of a chemical reaction in which the adhesive cures as it dries. Epoxy is used in fiber optic applications to adhere a connector ferrule to the fiber.

EPROM - Erasable Programmable Read Only Memory. A device that can store information (instructions or data) and retain it when power is removed. An EPROM is erased by exposing it to ultraviolet light. New information is loaded into the EPROM using a PROM programmer or “burner.” Also see "Flash memory."

EQ (Audio) - Equalizer. An audio signal processor used to add or attenuate frequencies in order to change the character of the resulting sound. EQ’s are properly used with a reference signal (see pink noise) and a real- time analyzer to ensure that the sound from the speakers closely matches the original sound.

EQ (Video) - Equalization. Selective amplification (signal restoration) applied to a signal to compensate for high frequency attenuation and other distortions encountered in long lengths of cable.

Equalizing pulses - These pulses cause the vertical deflection to start at the same time in each interval. They also keep the horizontal sweep circuits in step during the portions of the vertical blanking interval immediately preceding and following the vertical sync pulse.

Error Concealment - A method of concealing and hiding the impact of data lost during transmission. In video streaming systems, error concealment prevents lost network packets from disrupting a video frame or sequence of video frames.

Error Correction - A method of detection errors and reconstructing the original information using extra, redundant information sent along with the original data.

Error detection and correction - The ability to detect errors caused by interference or other factors during the transmission of a signal, and then reconstruct the received signal so that it is a faithful reproduction of the original signal, without errors. A process known as Forward Error Correction is often used to allow the receiver to detect and correct some errors without having to “ask” the transmitter to send additional data.

Error propagation - A single error experienced, produces a knock on effect to sequential information. In video streaming solutions decoding products should provide a method by which a single error encountered affects only a small area of a picture and should not affect an entire frame or sequential frames of video.

Ethernet - A Local Area Network (LAN) standard officially known as IEEE 802.3. Ethernet and other LAN technologies are used for interconnecting computers, printers, workstations, terminals, servers, etc. within the same building or campus. Ethernet operates over twisted pair and over coaxial cable at speeds starting at 10Mbps. For LAN interconnectivity, Ethernet is a physical link and data link protocol reflecting the two lowest layers of the OSI Reference Model.

Ethernet MAC Frames - A digital data transmission unit or data packet that includes frame synchronization information and a data payload. The synchronization data makes it possible for the receiver to detect the beginning and end of the packet in the stream of symbols or bits.

Expansion slots - Slots inside a cabinet that are used to connect additional circuit modules (cards).

Extrinsic Joint Loss - The portion of optical signal loss at a joint that is not intrinsic to the optical fibers, usually caused by misalignment between the fibers, end separation, and imperfections in the end finish of either fiber.

Extron - A shoutout to Extron for providing the majority of this glossary.

Eye Pattern - The representation of a digital signal on an oscilloscope in which a digital data signal is repetitively sampled. Distortion in the signal waveform due to interference and noise appears as closure of the eye pattern. Signals that are poorly synchronized with the system clock (also known as jitter), too high, too low, too noisy, too slow to change, or which have too much undershoot or overshoot, can be observed from the eye pattern. Eye patterns are used to evaluate the quality of digital signals when passed through cables or signal extension devices, switchers, signal processors, and other electronics.


F connector - A type of plug used for RF video connections, such as those used to connect TV antennas and cable TV to televisions and VCRs.

Fabry-Perot – FP - A standard laser diode that uses a laser oscillator comprised of two mirrors with an amplifying medium between them.

Fade, Fade-to-black - A gradual dissolve to another picture, often an all black screen.

Fan-Out Kit - In fiber optics, a kit designed for use with loose tube cable with bare fiber bundles in each buffer tube. The kit enables termination as well as protection of these bare fibers.

Far end - In videoconferencing, the party or group you are connecting to at the distant site.

Farad - Unit of measurement for capacitance which stores one coulomb of electrical charge when one volt is applied. More commonly, stated in picofarads, or one-millionth of one-millionth (10e-12) of a farad.

Fault - In fiber optics, any part of an optical fiber that deviates from normal performance.

Fault Finder - A simplified optical time domain reflectometer – OTDR, an instrument used to detect breaks within a run of optical fiber. Also known as a Fiber Break Locator.

FCC - Federal Communications Commission. The US governmental agency that controls and makes all policy for the use of broadcast airwaves.

FED - Field Emissive Display. FED technology is similar in operation to CRTs in that phosphor is excited by a stream of electrons traveling through a vacuum. “Emissive” refers to the light-emitting characteristic of the display; unlike LCD flat panel displays, a backlight is not required for image display. Because FEDs are emissive, they allow equal brightness at all viewing angles.

Feedback - (also known as Larson effect) The phenomenon where the sound from a loudspeaker is picked up by the microphone feeding it, and then reamplified again and again. The resulting loop between audio input (the microphone) and audio output (the loudspeaker) results in a scream or squeal emitted from the loudspeaker. Feedback is determined by the resonant frequencies in the amplifier and loudspeakers, the acoustics of the room, the design of the microphone, and the relative positions of the microphone and loudspeaker.

FEP - Fluoro Ethylene Polymer. Teflon FEP is used as a Foaming Dielectric for all of our Plenum Rated Coax Products

Ferrule - A precision tube which centers an optical fiber and provides stabilization and precise alignment. A ferrule may be part of a connector or a mechanical splice.

Ferrule Connector – FC - A screw-type optical fiber connector that features a keying mechanism. FCs are typically designated as FC/PC, FC/SPC, or FC/APC to denote physical contact, super physical contact, or angled physical contact, respectively.

FFT - Fast Fourier Transform. Converts analog waveforms into a form that can be easily analyzed for DSP applications.

Fiber - The basic optical transmission element. The components of a fiber include the core, surrounded by the cladding, and then a coating for protection. Specific optical properties of the core and cladding enable light to be contained within the core as it travels along the fiber.

Fiber Break Locator - An instrument used as simplified method of locating breaks within an optical fiber. Also known as a Fault Finder.

Fiber Coating - A coating surrounding the cladding of an optical fiber during the draw process to protect the fiber from handling and the environment.

Fiber Distribution Unit – FDU - An enclosure that houses and organizes groups of optical fibers.

Fiber Optic Cable - A telecommunications cable comprising one or more optical fibers.

Fiber Optics - The transmission of light through optical fibers for telecommunications applications.

Fiber Surface Finish - A term describing or denoting the quality of the polishing at the end of a fiber.

Fiber to the Building/Business – FTTB - Fiber optic service to a business or building.

Fiber to the Curb – FTTC - Fiber optic service to a node within a residential neighborhood. The node in turn feeds several homes via copper wiring.

Fiber to the Desk – FTTD - Fiber optic runs to individual desktops.

Fiber to the Home – FTTH - Fiber optic service to individual homes.

Fibre Channel - An industry standard for connecting computers for gigabit-speed transmission over twisted pair and optical fiber at distances up to 10 km.

Field - A field is one half of a standard television frame, containing every other line of information. Each standard video frame contains two interlaced fields, sometimes referred to as field 1 and field 2. In the NTSC video system, a field contains 262.5 lines and a frame contains 525 lines. In the PAL video system, a field contains 312.5 lines and a frame contains 625 lines.

Figure 8 - In fiber optics, a method of polishing the end of a connector in a figure 8 pattern to minimize scratches.

File - In computers, a record of related information that may be stored in memory, on a disk, or other media. Files can contain text, graphics, data, or programs.

Fillers - Non-conducting materials incorporated into the construction of a fiber optic cable to add roundness, flexibility, tensile strength, or a combination of all three.

Filter - In general, a filter accepts the desired and rejects the undesired. Every filter has a specific purpose. In electronics, for example, if you have some high frequency noise mixed with the signal that you want, then a lowpass filter is used to pass the signal and reject the (high frequency) noise. In software, a filter allows the application to open a file of a specific format. Also see "Band pass filter", "High pass filter", and "Low pass filter."

Firewall - A device that manages access of devices outside a network into a network, typically into a building or an enterprise. A firewall prevents unauthorized access to a network.. They are also used to check on data delivered to and from a network to ensure the information is non-damaging.

FireWire™ - A trademark of Apple. Also known as 1394 or IEEE-1394. A data communication standard used primarily with digital camcorders, 1394 FireWire manages the data transfer and tape transport control processes when transferring DV (digital video) to your computer or DV editing system. FireWire supports data transfer rates of 100 to 400 Mbps.

First surface mirror - The front of a mirror. In mirrors intended for A/V applications, the first surface is coated with a reflective material to prevent double images (ghosting).

FL - Focal Length. The distance between the center of a lens and the point where the image comes into focus. In projection, a shorter focal length yields a larger image on the screen for any given projection distance.

Flash memory - A special version of an EEPROM that can be rewritten while in its functioning environment, instead of having to be removed and reprogrammed in a special device. Example: memory for a digital camera.

Flat (response) - A theoretical ideal for audio components, especially speakers, that represents a frequency response that does not deviate from a flat line over the audible frequency spectrum. A flat response, though ideal, is impossible in real world listening due to the speaker itself and its interactions with the room and various surfaces within the room. All speakers will fluctuate above and below the ideal flat response, but speakers that stay within two or three dB of a flat response are considered very linear and very nearly flat in their response.

Flat field - A solid field of color used to calibrate monitors and projectors. A full white flat field is typically used to evaluate the uniformity of a projected image.

Flat polish - In fiber optics, a condition at a ferrule where the endfaces of a fiber optic cable and the ferrule tip are polished flat.

Fletcher-Munson effect - Also referred to as “equal loudness contours.” Fletcher and Munson, researchers at Bell Labs, first measured the sensitivity of human hearing at various volumes and frequencies. Fletcher and Munson found that human hearing is dependent on loudness, and that the ear is most sensitive in the range of 3 kHz to 4 kHz. Sensitivity falls off rapidly at lower frequencies and somewhat more slowly at higher frequencies. Sounds in frequencies below and above this range need to be louder (more powerful) in order to be heard clearly. The loudness control found on audio reproduction systems is designed to compensate for the Fletcher-Munson effect.

Flicker - An alternating change of light intensity, typically perceived at a rate of a few Hertz to 60 Hz when viewing static images such as text. Flicker can occur when the electron gun paints the screen too slowly, giving the phosphors on the screen time to fade before being refreshed. This may occur when the refresh rate of the video is too low, or when the persistence of the display device is too short. A fluorescent light fixture may produce the same effect.

Fluoropolymer - Describes Teflon® FEP in generic terms. FEP – Fluorinated Ethylene Propylene is a compound used in the construction of cable jacketing and insulation. It is resistant to chemicals, withstands a broad temperature range, and exhibits excellent electrical properties.

Flutter - Pitch variations heard as a fast wavering or wobbling caused by an audiotape or CD moving at varying speeds. Also see "Wow."

FM - Frequency Modulation. A method of combining an information signal with a carrier signal so that it may be transmitted. FM radio is frequency modulated. Audio is encoded on the carrier by varying the frequency in response to the audio.

Focus - To adjust a lens to make the image appear sharp and well defined. The best possible resolution of an image, showing the image to be sharp and well defined.

Focus coil - Deflection coil. An electromagnetic coil that surrounds a video tube and bends the electron beam onto a screen.

Foot candle - A unit of illumination from one candle at a distance of one foot. Equal to one lumen incident to one square foot.

Foot lambert - A unit of luminance measurement used in the US for determining the level of brightness reflected from a projection screen or emitted from a display in a 1-foot x 1-foot area. Total luminance values are calculated using display lumens and screen area to determine appropriate level of brightness needed for a given environment.

Forward Error Correction (FEC) - A system of error control for data transmission, whereby the sender adds redundant data to its messages, also known as an error correction code. This allows the receiver to detect and correct errors (within some bound) without the need to ask the sender for additional data. The amount of FEC required to guarantee delivery is not certain. Each application must consider the predictability of the network and the amount of protection that is desired.

FOTS - Fiber Optic Transmission System.

FPC - Front Panel Controller, Extron’s term for the front panel control system used with larger matrix switchers such as the Matrix 3200/6400 and Matrix 12800 series models. The FPC provides simple, touch-of-a-button control of the matrix switcher and eliminates the need for a computer or third party control system to operate the matrix switcher.

fps - frames per second. A measure of information that is used to store and display motion video. Each frame represents a still image and displaying frames in succession creates the illusion of motion. The more frames per second (fps), the smoother the motion appears.

Frame - In interlaced video, a frame is one complete picture. A video frame is made up of two fields, or two sets of interlaced lines. In film, a frame is one still picture of a series that makes up a motion picture.

Frame Lock - Multiple video sources delivered together, which maintain frame synchronization are frame locked. Frame lock is required for delivery of stereoscope 3D imagery consisting of two locked signals or 4k resolution images which are built up using four, synchronized HD video signals.

Frame Rate - The frequency at which an imaging device produces unique, consecutive images called frames. The term applies equally to computer graphics, video cameras, film cameras, and motion capture systems. Frame rate is most often expressed in frames per second (FPS) and sometimes in progressive scan monitors as hertz (Hz). It can also be seen as refresh rate or vertical scan rate.

Frame Relay - Public, connection-oriented packet service based on the core aspects of the Integrated Services Digital Network. It eliminates all processing at the network layer and greatly restricts data-link layer processing. It allows private networks to reduce costs by using shared facilities between the end-point switches of a network managed by a Frame Relay service provider. Individual data-link connection identifiers (DLCIs) are assigned to ensure that each customer receives only its own traffic.

Frame synchronizer - Stores each incoming frame of video and releases it as the next frame comes in. Frame synchronizers convert analog video to digital and are typically used to synchronize two or more sources.

Frequency - The number of times a particular event happens per a given time. In A/V, the number of complete cycles per second of a musical tone or electronic signal, expressed in Hertz (Hz).

Frequency Division Multiplexing – FDM - The combining of two or more signals into a single carrier signal for transmission through FM – frequency modulation. Each signal modulates the carrier signal at a different region of the frequency spectrum.

Frequency domain - The means of representing a signal as a plot of amplitude (normally on the vertical axis) versus frequency (normally on the horizontal axis). A spectrum analyzer represents signals in the frequency domain. Also see "Time domain."

Frequency range (audio) - The range of frequencies between high and low end points; for example, in audio, the frequency range of the human ear is said to be 20 Hz to 20,000 Hz. Individual speaker elements like woofers, midranges and tweeters serve different frequency ranges within the overall audio frequency range.

Frequency range (video) - Refers to the low-to-high limits of a device, such as a computer, projector, or monitor. Also see "Color phase."

Frequency response - The frequency range over which signals are reproduced within a stated amplitude range. Generally expressed in Hz vs. dB. For example: 100 - 5000 Hz +/- 3dB means that the device can handle a frequency range of 100 to 5000 Hz with a possible deviation in amplitude within that frequency range of +3 to -3dB.

Fresnel lens - A thin, flat lens made by cutting concentric circular grooves into its surface. The grooves act like prisms to bend and focus light. The Fresnel lens is often used for the condenser lens in overhead projectors and in studio spotlights.

Fresnel reflection - The partial reflection of light that occurs at the boundary between two materials with different indexes of refraction. In fiber optics, this is considered a loss when light is partially reflected at a glass-air interface.

Front porch - The black or blanking portion of the composite picture signal lying between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding horizontal sync pulse. Also see "Blanking."

Front projection screen - A light-reflecting screen used when the image is projected from a source in front of the screen. Also see "Rear projection screen."

Front screen projection - To project an image from the audience’s side of a light-reflecting screen.

FTP - File Transfer Protocol. A protocol used to transfer files over a TCP/IP network (Internet, UNIX, etc.). For example, after developing the HTML pages for a Web site on a local machine, they are typically uploaded to the Web server using FTP.

Full duplex - The ability of a device or line to transmit data simultaneously in both directions.

Full Duplex Operation - When data is being both sent and received simultaneously. (i.e., sound cards, network interface cards, hubs)

Fully loaded - Refers to the condition when all inputs (in the case of a switcher) or all outputs (in the case of a distribution amplifier) or both (in the case of matrix switchers) are connected to loads/devices, that is, the product has a maximum load connected. This is pertinent because if a product is not properly designed, the voltage and the bandwidth can decrease and the signal can drop out as more and more loads are connected, or crosstalk can be a greater problem as more signals appear on the inputs or outputs.

Function keys - Keys that are programmed to perform specific tasks, such as macro-operations.

Fundamental rejection - Usually expressed in dB, the amount by which a total harmonic distortion (THD+N) analyzer rejects the fundamental component of the input signal. The lowest measurable distortion of THD+N analyzer is limited by the fundamental rejection, along with several other attributes. Also see "THD" and "THD+N."

Fusion splicer - An instrument that is used to bond, or fuse two optical fibers together by heating, usually generated by a high intensity electrical arc.


Gain - (1) A general term for an increase in signal power or voltage produced by an amplifier. The amount of gain is usually expressed in decibels above a reference level. Opposite of attenuation. (2) The amplification of a signal, unit, or system. Expressed in the unit of measurement appropriate to the signal or system. (3) In fiber optics applications, the measurement of back reflections using an OTDR - Optical Time Domain Reflectometer, due to a mismatch in core sizes between adjoining optical fibers.

Gainer - In fiber optics applications, a backscatter measurement condition with an OTDR that indicates a splice loss, due to a mismatch in core size between the two optical fibers. The resulting trace indicates a perceived increase in power, and is therefore known as a “gainer.”

Gamma - The light output of a CRT is not linear with respect to the voltage input. The difference between what you should have and what is actually output is known as gamma.

Gamma correction - Before being displayed, the linear RGB data must be processed (gamma corrected) to compensate for the gamma of the display.

Gang - Refers to the number of wiring devices that can be installed in an electrical box, (e.g., “two gang” refers to a box that can accommodate two duplex receptacles, “three gang” refers to a box that can accommodate three duplex receptacles, etc).

Gateway - A network node equipped for interfacing with another network that uses different protocols. Also can be described as an entrance and exit into a communications network.

Genlock - A technique where the video output of one source, or a specific reference signal, is used to synchronize other television picture sources together. Video sources which are genlocked have vertical sync pulses which are synchronized together.

Ghost - Also called “ghosting,” or “reflections.” A shadowy or weak duplication of the original image. It can be the result of transmission conditions where secondary signals are created and then displayed earlier or later than the original signal. Ghosts can also be the result of burning an image on a screen or by a mirror.

GHz - Gigahertz. One billion cycles per second.

Giga - The prefix abbreviation for billion. (G) One G-Byte = 1 billion bytes.

Global presets - The Extron matrix switcher output configuration settings that can affect all output connections/ties and can be saved/recalled by simply pressing a button or issuing a Simple Instruction Set (SIS™) command.

GOP - Group of successive pictures within a coded video stream. MPEG, MPEG-2 and MPEG-4 compression products apply a GOP structure to their video compression systems. Each coded video stream consists of successive GOPs. From the pictures contained in it, the visible frames are generated. A GOP begins with an I-frame containing the full temporal resolution of the video frame. A series of predictive information is calculated between I –frames. P-frames are predictive and estimate forward, B-frames apply bi-directional prediction and estimate forwards and backwards. Products will apply GOP structures in different manners to support the needs of different applications be it: low delay, low bit rate or error resilience.

Graded index fiber - An optical fiber in which the index of refraction within the core of a multimode fiber decreases with the radius from the fiber axis. The index of refraction usually follows a parabolic profile from the fiber axis to the cladding, effectively addressing modal dispersion throughout the fiber link.

Graded Index Plastic Optical Fiber – GI-POF - A plastic multimode optical fiber with an index of refraction within the core that decreases from the fiber axis to the cladding. The index of refraction usually follows a parabolic profile from the fiber axis to the cladding, effectively addressing modal dispersion throughout the fiber link.

Graphic equalizer - An active electronic device which allows the adjustment of narrow ‘bands’ of audio frequencies to correct for recording and listening room deficiencies. Graphic equalizers generally have sliding levers, known as faders, representing the different ranges of frequencies between 20 and 20,000 Hz. (See EQ-Audio)

Ground - Electrical connection of a circuit to a point designated as having zero potential.

Ground loop - A potential system grounding problem that may produce symptoms that appear as sync noise and cause a horizontal bar (hum bar) to roll vertically on the video image. A ground loop occurs when some devices in a system are not connected to the same electrical ground as the other devices. This can create a voltage potential difference between ground on the pieces of equipment.

Group delay - The amount of delay or rate of phase shift with respect to frequency though a device or cable.

GVIF - Gigabit Video Interface. A transmission and connectivity standard developed by Sony that is used for digital video connections on the Sony VAIO desktop computer systems and Sony laptop PCs.


H — - See "Horizontal sync."

H.264 (MPEG-4 AVC) - Block-oriented motion-compensation-based codec standard developed by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC Moving Picture Experts Group (MPEG). It is the product of a partnership effort known as the Joint Video Team (JVT). H.264 is used in such applications as Blu-ray Disc, videos from YouTube and the iTunes Store, DVB broadcast, direct-broadcast satellite television service, cable television services, and real-time videoconferencing.

H.264 Encoding - A standard for video compression equivalent to MPEG-4 Part 10 or MPEG-4 AVC – Advanced Video Coding. H.264 was created to provide video quality suitable for high definition applications at bit rates lower than that utilized in MPEG-2, the compression standard used in DVD authoring.

H.320 - ITU-T H.320 is a family of standards developed for video teleconferencing systems using ISDN. It references H.261 (for video); G.711, G.722, and G.728 (for audio); H.221, H.230, H.231, H.233, H.234, H.242, and H.243 (for control). The standard allows a system from one manufacturer to talk to a system from another manufacturer, just as two different brands of FAX machines can talk to each other.

H.323 - ITU standard allowing audio, video, and data to be transmitted by way of the Internet Protocol (LAN/WAN). It is the umbrella standard defining multiple codes, call control, and channel setup specifications. Basically, videoconferencing over IP.

Half duplex - Data or audio transmission that can occur in two directions over a single line, but only one direction at a time.

Halogen-free (LSFOH) - Low Smoke and Fumes Zero Halogen. Refers to the material used in cable insulation that emits reduced amounts of hazardous smoke and toxic fumes in the event of a fire. Certain countries, such as in the UK, may require LSFOH cable insulation.

Handshake - In communications, the moment when the transmitting and receiving devices identify themselves to each other.

Harmonics (in music: overtones) - Multiples of an original frequency that add to and modify the original frequency. A pure sine wave is free of harmonics. When harmonics occur in electronic signals, it adds distortion to the original signal, causing undesirable results.

HD connector - A high-density D connector having its pins arranged close together, sometimes in three rows instead of two rows. Example: a 15-pin VGA connector (HD) vs. a Mac connector (D).

HDCP – High-bandwidth Digital Content Protection - A digital rights management scheme developed by Intel to prevent the copying of digital video and audio content. HDCP is mandatory for the HDMI interface, optional for DVI. HDCP defines three basic system components: source, sink, and repeater.

Sources send content to the display. Sources can be set-top boxes, Blu-ray Disc players, computer-graphics cards, and so forth. A source can have only one HDCP transmitter.

Sinks decrypt the content so it can be viewed. Sink is typically used to describe a flat panel display, television, or projector. Sinks can have one or more HDCP receivers.

Repeaters sit between Sources and Sinks. They accept content, decrypt it, then re-encrypt and transmit. Internally, a Repeater may provide signal processing, such as scaling, splitting out audio for use in an analog audio playback system, or splitting the input data stream for simultaneous viewing on multiple displays. Switchers, matrix switchers, and distribution amplifiers are all examples of Repeaters.

HDMI – High-Definition Multimedia Interface - An interface for the digital transmission of uncompressed high definition video, multi-channel audio, and control signals, over a single cable. HDMI is the de facto standard for consumer level video sources and displays.

HDR - High Dynamic Range is a video display technology that greatly increases the range between light and dark, so that more of what the eye sees in real life is visible. Different HDR systems include Advanced HDR by Technicolor, Dolby Vision, HDR+, HDR-10+, and HLG. An HDR TV set and HDR-encoded content is required. More become available every day.

HD-SDI - The high-definition version of SDI specified in SMPTE-292M. This signal standard transmits audio and video with 10 bit depth and 4:2:2 color quantization over a single coaxial cable with a data rate of 1.485 Gbit/second. Multiple video resolutions exist including progressive 1280x720 and interlaced 1920x1080 resolution. Up to 32 audio signals are carried in the ancillary data.

HDTV - High Definition Television. HDTV refers to a complete product/system with the following minimum performance attributes: a receiver that receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format with active vertical scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher; aspect ratio capabilities for displaying a 16:9 image; receives and reproduces, and/or outputs Dolby Digital audio.

Hertz (Hz) - A unit of frequency; describing the number cycles per second. 1Hz = 1 cycle/second…1MHz = 1 Million cycles/second

High fidelity - Hi fi, accurate, and faithful reproduction of the original. Absence of distortion or enhancements.

High impedance - Hi Z or high Z. A relative term that is different for each application. In video, when the signal is not terminated it has a Hi Z load. Hi Z is typically 800 to 10k ohms or greater.

High pass filter - A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass. Also called a “low cut filter.”

High-Definition Video - Refers to any video system of higher resolution than standarddefinition (SD) video, and most commonly involves display resolutions of 1280×720 pixels (720p) or 1920×1080 pixels (1080i/1080p).

Hooking - See "Bending."

Hop - In a packet-switching network, a hop is the trip a data packet takes from one router or intermediate point to another in the network.

Hop Count - On the Internet (or a network that uses TCP/IP), the number of hops a packet has taken toward its destination.

Horizontal blanking - After making a scan line (left-to-right), the electron beam in a CRT retraces (returns) to the left side of the screen to begin the next line. During retrace time, it is not putting picture information on the screen, so the beam is turned off, or blanked. About 83% of each horizontal cycle is spent writing the line, while 17% is spent retracing the beam to the left before starting the next line. Also see "Blanking."

Horizontal Cabling - Telecommunications cabling used to cover a floor area. It extends from the horizontal cross-connect in the telecommunications room to a local access outlet.

Horizontal centering control - Adjusting the horizontal centering control shifts the displayed image left or right on the display screen. Also called “horizontal shift.”

Horizontal Cross-Connect – HC - A patch panel or LAN – Local Area Network panel, used to cross-connect horizontal cables to other cabling within a building or facility.

Horizontal double images - A video problem when the display is split down the middle with two identical but squeezed images displayed on each side of the screen.

Horizontal filtering - In some Extron scan converters and other products, this is a feature that controls the sampling of the horizontal plane, thereby affecting the sharpness or smoothness of the scan-converted picture.

Horizontal rate - Horizontal scanning frequency. The number of complete horizontal lines (trace and retrace) scanned per second. Measured in kHz, the NTSC standard is 15.75 kHz.

Horizontal resolution - The number of vertical lines that can be perceived in a video device.

Horizontal sync - The pulses that control the horizontal scanning of the electron beam in a video device. On connector panels, “H” identifies the connector for horizontal sync, and “H/HV” means it is also used for combined or “composite” horizontal and vertical sync (RGBS).

Hot Plug/Hot Plug Detect - Describes a feature of DVI, HDMI, USB, and other digital technologies which allows a host device, such as a computer, to detect the presence of a new device without intervention by the user. Hot Plug technology allows a new device to be added to a system while it’s still connected to a power source. Once the new device is connected, the Hot Plug Detect circuit, or HPD, senses the new device and tells the rest of the system that the device is ready to either send or receive a data stream.

Hot spot - Commonly seen on high-gain screens and screens designed for slide or movie projection, a hot spot is a circular area where the image is brighter than the rest of the screen. The hot spot is always located along the line of sight, and “moves” with the line of sight.

Hot-swap - The ability to change electronic components, such as circuit boards or peripheral devices, without removing power from the device.

House sync - See "Blackburst."

HDBaseT is a connectivity standard for whole-home and commercial distribution of uncompressed HD multimedia content. The cornerstone of HDBaseT technology is 5Play™, a feature set that converges uncompressed full HD digital video, audio, 100BaseT Ethernet, power over cable and various control signals through a single LAN cable.

HTML - Hypertext Markup Language. A formatting computer language used to create web pages.

HTTP - HyperText Transfer Protocol. A Web protocol based on TCP/IP that is used to retrieve hypertext objects from remote Web pages.

HTTPS - Hypertext Transfer Protocol Secure. It is HTTP layered on top of the SSL protocol. It is used for secure communication over a network and is widely used on the Internet.

Hub - A shared transmission media to which devices on a network are interfaced. Ethernet hubs have mostly given way to Ethernet switches.

Hue - (1) Color value or saturation, as opposed to brightness or intensity. (2) Tint control – Hue is the parameter of color that allows us to distinguish between colors. The hue, or tint control, adjusts the amount of color displayed.

Huffman Coding - A method of entropy encoding used in lossless data compression where the most frequently occurring values use the shortest codes.

Hum - The coupling of an unwanted frequency into other electrical signals. In audio, hum can be heard; in video, it can appear as waves or bars in the picture. Often it is an audible disturbance caused by the power supply, or an improper ground.

Hum bar(s) - Interference in the form of a horizontal bar moving vertically on the display screen. Hum bars can be caused by ground loops.

Humbucker - A transformer used to isolate video signals caused by interference from hum bars or moiré.


I/O - Input/Output. Refers to the flow of information or signals (in or out) with respect to a particular device.

ICIA - International Communications Industries Association. A professional A/V, video, and multimedia industry association.

ICT – Image Constraint Token - Part of AACS, the Blu-ray Disc digital rights management system, the Image Constraint Token can cause the output of a Blu-ray Disc player to be down-converted to low-resolution video, similar in quality to a DVD. AACS requires that all components in the display chain, from the source to the display device, to be secured through HDCP or DPCP content protection. If the ICT flag is set and the Blu-ray player is connected to a device that does not support HDCP, for example an analog television or video recorder, the player automatically reduces the high-definition video quality to a maximum of 960x540 pixels before outputting it.

ICWK - Internal Computer Wiring Kit. Custom ICWK kits provide interfacing signals for computers and terminals that have no video display output connector.

ID bit termination - Used to identify what type of display device is attached to a computer-video output port. ID bit termination involves connecting specific data lines or “pins” to the electrical ground. ID bit termination assures that the correct video signals will be sent to the display device. A computer checks for ID bits during the power-up self diagnosis, and sets the video output frequency and resolution based on how the ID bits are set. Some computers will not send any video signal if they do not sense any ID bits on boot-up, so no picture will be displayed. ID bits are also called “sense lines.”

IEC - International Electro-technical Commission. The body that has responsibility for developing international A/V standards. ICIA cooperates with IEC sub-committee SC-60.

IEC connector - The standard AC power connector used on power supplies in computers and other electronic equipment. It accommodates a power cord with a connector on both ends.

IEEE - Institute of Electrical and Electronic Engineers. The IEEE is an industry organization that undertakes the development of standards for electronic interfaces, wireless and wired networks, and related technologies.

IEEE 1394 - Institute of Electrical and Electronics Engineers standard 1394. Also known as FireWire (a trademark of Apple) and i.Link (a trademark of Sony), IEEE 1394 is a serial digital format that handles a wide range of data. IEEE 1394 offers peer-to-peer interface capability, so it does not require computer support.

IEEE 802.11 - The Institute for Electrical and Electronics Engineers standard for wireless Ethernet networks. IEEE 802.11 applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS).

IEEE 802.11a - An extension to 802.11 up to 54 Mbps in the 5GHz band. IEEE 802.11a has a data transmission rate capability sufficient for the delivery of “live” or full motion standard definition video.

IEEE 802.11b - Often called Wi-Fi, 802.11b is backward compatible with 802.11. IEEE 802.11b has a data transmission rate of 11 Mbps, sufficient for most non-motion data transmission applications.

IEEE 802.11g - Applies to wireless LANs and provides 20+ Mbps in the 2.4 GHz band. This is the most recently approved 802.11 standard and offers wireless transmission over relatively short distances at up to 54 megabits per second (Mbps), compared with the 11 megabits per second of the 802.11b standard. Like 802.11b, 802.11g operates in the 2.4 GHz range.

IEEE 802.11n - Upcoming wireless standard that builds upon 802.11 standards by adding Multiple Input Multiple Output (MIMO) technology. MIMO uses multiple transmitter and receiver antennas to increase the data rate, promising between 100-200 Mbps. 802.11n is expected to be ratified in late 2006 or early 2007.

IEEE 802.3 - The Institute for Electrical and Electronics Engineers standard for Ethernet networks.

IGMP - Internet Group Management Protocol. Host-to-router signaling protocol for IPv4 to report their multicast group memberships to neighboring routers and determine whether group members are present during IP multicasting. Similarly, multicast routers, such as E-Series routers, use IGMP to discover which of their hosts belong to multicast groups and to determine if group members are present.

IGMP Snooping - IGMP snooping, as implied by the name, is a feature that allows a switch to “listen in” for multicast join requests on a network and deliver to end-point network devices when requested. A switch which supports IGMP snooping will not flood all of its ports with multicast traffic. IGMP snooping is supported in layer 3 switches and some layer 2 switches.

ILA® - Image Light Amplifier. Used in their large screen projectors, a Hughes-JVC device that uses low-intensity images to modulate high-intensity light through a liquid crystal layer.

Illuminance - The light density (the luminous flux divided by area) shining onto a surface. This is the specification that measures how bright a screen is lit by a projector or ambient light. The unit is lux. 1 lux = 1 lumen/m2.

Image - A reproduction or imitation of a person or thing displayed by any type of visual media.

Image noise - The random variation of brightness or color information in images produced by the sensor and circuitry of a scanner or digital camera.

Impedance - The opposition or load to a signal, measured in ohms and abbreviated W or Z. In video, typical low impedance circuits (low Z) are 600 ohms or less and high impedance circuits (high Z) may be 10 k ohms or greater. Video termination impedance is 75 ohms. Also see "High impedance" and "Low impedance."

Impedance matching - Circuits that generate audio or video signals are designed to work with a certain load (impedance). When connecting devices in a system, it is important that the impedance specifications are adhered to. If the impedance of the load is not matched to that of the source, there could be undesirable results, such as loss or distortion of the original signal, reflections, etc.

IMUX - Inverse multiplexer. A unit that combines multiple low bandwidth digital phone lines into a single high bandwidth call.

Index matching gel - A special gel with an index of refraction similar to that of the optical fiber core. It is applied at the fiber endface to minimize loss due to Fresnel reflection in mechanical splices or cleave and crimp connectors.

Index matching materials - Materials with an index of refraction similar to that of the optical fiber core. They are applied at the endfaces of adjoining optical fibers to minimize losses due to Fresnel reflection.

Index of refraction - The ratio of the speed of light in a vacuum to the speed of light in a material. Also known as the refractive index.

Inductor - An electrical component that opposes changes in current flow and stores electrical energy as a magnetic field. Although all wires have inductive properties, an inductor component is usually a coil of wire. Transformers use this same principle.

Infrared (IR) - Light waves just outside the visible spectrum, slightly longer than those visible to the human eye. Infrared light is sometimes filtered out to reduce heat on film or slides. Also see "Infrared control."

Infrared control - A wireless medium of remote control, which sends signals to a device via pulses, transmitted in the infrared light spectrum. Its use is restricted to equipment within line-of-sight or reflections off a wall or ceiling. This is sometimes called “IR remote.”

Infrared Remote -

Injection Laser Diode – ILD - A laser in which the lasing, or stimulated emission of coherent light, occurs at the p-n junction of a semiconductor.

Inline splice closure - An enclosure which houses the spliced fiber optic cable and provides cable ports at opposite ends.

Innerduct - A duct, usually non-metallic, that may be placed within cable trays or HVAC ducts, to be used as conduit for installation of fiber optic cables.

Input sensitivity - The minimum input level signal required to output a specified output level.

Insertion loss - The loss of optical power as a result of incorporating components such as connectors, couplers, or splices into an optical fiber system.

Inspection scope - A microscope specifically for inspecting fiber optic connectors.

Interbuilding backbone - A backbone network that provides communication between buildings, such as on a university or corporate campus, or military installation.

Interface - (noun) A device or module that operates as a link between dissimilar modules, usually because those modules cannot communicate directly with each other. An interface may act as a translator or interpreter and could be in the form of hardware and/or software. A computer video interface allows computer-video signals to be used by large screen video displays

Inter-Frame Coding - A compression technique which spans multiple frames of video and eliminates redundant information between frames.

Interlace - In TV, each video frame is divided into two fields with one field composed of odd numbered horizontal scan lines and the other composed of even numbered horizontal scan lines. Each field is displayed on an alternating basis.

Interlacing - A video frame is made up of two fields. Interlacing is the process of scanning the picture onto a video screen whereby the lines of one scanned field fall evenly between the lines of the preceding field.

Interleaving - The process of assigning consecutive physical memory addresses alternately between two memory controllers to increase the effective transfer rate.

Intermediate Cross-Connect – IC - A cross-connect, usually a patch panel, used to provide backbone cabling between the MC - Main Cross-Connect and HC - Horizontal Cross-Connect.

Intermediate Distribution Frame – IDF - In telecommunications applications, a metal rack, located in an equipment room or closet, that provides connection between interbuilding cabling and the intrabuilding cabling.

Intersymbol interference – ISI - In fiber optics, the interference between adjacent digital bits in a serial digital stream caused by pulse spreading in an optical fiber. Pulse spreading in an optical fiber due to dispersion in an optical fiber.

Intrabuilding backbone - The backbone network within a building that provides communications to individual offices and users.

Intra-Frame Coding - A method of video compression that compresses information within a single frame.

Intra-prediction - Intra-prediction is an advanced compression technique applied in H.264 which takes advantage of the spatial redundancy within a frame to reduce the amount of data required to encode an I-frame.

Intrinsic Losses - Losses due to inherent differences in the characteristics of the optical fibers being spliced.

IP (Internet Protocol) - Internet Protocol defines addressing methods and structures for datagram encapsulation allowing delivery of packets from a source to a destination based purely on addressing.

IP Address - A numerical label that is assigned to devices in a network, that uses the Internet Protocol. The IP address for the source and destination are included in an IP datagram.

IP Link® - Extron’s high performance IP integration technology specifically engineered to meet the needs of professional A/V environments.

IP netmask - A 32-bit binary number (12 digit decimal number— used on subnets (smaller, local networks) to help the router determine which network traffic gets routed internally to local computers and which network traffic goes out on the Internet.

IPv4 - Internet Protocol version 4. The legacy version of the Internet Protocol, which is the fundamental protocol on which the Internet is based. It is a connectionless protocol for use on packet-switched Link Layer networks (e.g., Ethernet). It operates on a best effort delivery model, in that it does not guarantee delivery, nor does it assure proper sequencing, or avoid duplicate delivery.

IPv6 - Internet Protocol version 6. This new Internet Protocol is designed to replace and enhance the present protocol which is called TCP/ IP, or officially IPv4. IPv6 has 128-bit addressing, auto configuration, new security features and supports real-time communications and multicasting. The primary equipment to apply IPv6 to is routing equipment, not source equipment.

IPX - Internetwork Packet Exchange Protocol. Commonly used over Novell Netware and Microsoft Windows networks.

IR learning - The ability of a device to receive and store infrared commands for other devices, such as the projector. Each command is assigned to a system operation (such as selecting an input). When an operation is executed, the associated (learned) command is then transmitted through an IR emitter or broadcaster to the projector, where it is executed. For example, if input #3 is S-video, selecting that input also sends a signal to the projector to switch to S-video mode.

IR library - Sets of infrared commands for video projectors are available at the Extron Web site (

IRE - Institute of Radio Engineers. Now called IEEE, the Institute of Electrical and Electronic Engineers. Also see "IEEE."

IRE scale - An oscilloscope scale that applies to composite video levels. Typically, there are 140 IRE units in one volt (1 IRE = 7.14 mV). This makes luma level values easier to communicate. The amplitude of the video signal from blanking (zero volts) to peak white is 0.714286 volts or 100 IRE units. Sync signals extend from blanking to 1.285714 volts/40 IRE units.

ISDN - Integrated Services Digital Network. An international communications standard for sending voice, video, and data digitally over telephone lines. ISDN uses special wires and can transfer at rates of 64,000 bits per second. Another version called B-ISDN uses fiber optics and can transfer at 1.5 megabits per second.

ITS - Information Transport System or Intelligent Traffic System

ITU - International Telecommunication Union. Formerly known as the CCIR (Comité Consultatif International des Radiocommunications) or International Radio Consultative Committee. A global organization responsible for establishing television standards.

ITU-R BT.601 - Formerly known as CCIR 601. A serial digital form of component video developed by the International Telecommunication Union for the digitization of color video signals. ITU-R BT.601 is the digital equivalent to Y, R-Y, B-Y, component analog video, and is transmitted on one coax cable instead of three. It is also called 4:2:2, which refers to the number of samples taken from each of the video channels: for every four samples of the Y (luminance) channel, the two color difference channels, R-Y and B-Y, are sampled twice.

ITU-R Recommendation BT.2020 - Defines parameters of ultra-high-definition television (UHDTV) including picture resolutions, frame rates with progressive scan, bit depths, color primaries, RGB and luma-chroma color representations, chroma subsamplings, and an opto-electronic transfer function. Commonly referred to as Rec. 2020 or BT.2020. The first version of Rec. 2020 was posted on the International Telecommunication Union (ITU) website on August 23, 2012.


Jacket - Outer protective covering of a wire or cable.

Jaggies - A video problem in which stairstep-like lines appear where there should be straight-angled lines or smooth curves. Also see "Aliasing."

Jitter - A video problem in which the displayed image is unstable or appears to shake.

JPEG (Joint Photographic Experts Group) - Commonly used method of lossy compression for photographic images using a discreet cosine transfer function. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality. Produces blocking artifacts.

JPEG2000 - A wavelet-based image compression standard and coding system. There is a modest increase in compression performance of JPEG 2000 compared to JPEG, the main advantage offered by JPEG 2000 is the significant flexibility of the codestream which allows for representing the image at various resolutions.

Judder - A motion artifact whereby image elements appear to move with stepped, rather than smooth, motion. Commonly occurring in content converted to 30 fps or 60 fps from a 24 fps or 25 fps source, video judder has multiple causes including errors in frame rate conversion, telecine pulldown detection, or deinterlacing.

Jumbo Frame - Ethernet frames with more than 1500 bytes of payload. Network switches typically process packets with a maximum transfer unit, MTU of 1500 bytes. Use of jumbo packets can increase transmission efficiency by reducing the network transmission overhead used for the Ethernet datagram wrapper which includes items such as the source and destination address.


K - kilo. An abbreviation for 1,000. A kilobyte is 1,000 bytes. Because numbers used in computer RAM sizes are in binary, the closest number is used. When talking about memory size, the numbers are rounded off (e.g. 1 kbyte is really 1,024 bytes).

Kell factor - The ratio between the measured number of TV lines and the pixel count of a fixed pixel video device. It equals 0.7. For example, a DVD picture with 720 pixels in the horizontal direction is equivalent to about 500 TV lines (720 x 0.7=500) of resolution.

Kelvin - An absolute scale of temperature measurement typically used to describe the color of light, expressed in “degrees Kelvin.” The lower the number, the “warmer” or redder the color of the light; a higher number indicates a “colder”, or bluer, light source. Also see "Color temperature."

Kevlar® - A brand name from DuPont for aramid yarn, used in the construction of cables to provide strength and strain relief.

Key - (1) Also called key source or key cut. A signal that can be used to electronically cut a hole in a video picture to allow for insertion of other elements such as text or another video image. The key signal is a switching or gating signal for controlling a video mixer that switches or mixes between the background video and the inserted element. (2) The composite effect created by cutting a hole in one image and inserting another image into the hole.

Key fill - In key effects, the video signal that is said to fill the hole cut in the background video by the key source.

Keyer - An electronic circuit that creates a control signal to control a video multiplier based on selective information contained in a video signal.

Keys - See "KSV – Key Selection Vector."

Keystone effect - A distorted picture where one edge is not the same dimension as the opposite edge, producing a tapered or wedge shape. Typically, this results when the image is projected to the screen at an angle. In stone buildings, the tapered stone at the top of an arch is the key that prevents the arch from falling.

kHz - Kilohertz. One thousand cycles per second (hertz).

KSV – Key Selection Vector - A unique numerical key used in content protection or digital rights management schemes such as HDCP. Keys are used to authenticate devices connected to one another, to ensure that a source is connected to a display and not a digital recording device.


Lambert - A unit of measure expressing the intensity of light reflected off an object. 1 lambert = 0.318 foot-candles per square centimeter.

LAN - Local Area Network. Supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.

Lapping film - Sheets of film used for polishing ferrule endfaces, comprising a film backing with mineral particles at various ratings for grit or coarseness.

Laser - Light Amplification by Stimulated Emission of Radiation. An optical source that generates coherent light within a narrow band of wavelengths.

Laser chirp - A sudden change in the center wavelength of a laser, caused by reflected or crosstalk optical energy entering the lasing chamber.

Laser-Optimized Multimode Fiber - A multimode fiber with higher bandwidth than legacy multimode fiber, designed for transmission with laser based sources such as VCSEL.

Latency - A measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. In video processing or encoding products, it is a measure of the amount of time used to process an input signal. In a packetswitched network it is measured either one-way (the time from the source sending a packet to the destination receiving it), or round-trip (the one-way latency from source to destination plus the one-way latency from the destination back to the source).

Layer 2 Switch - Layer 2 switches support functions of the 2nd layer of the ISO model. Layer 2 switches provide hardware switching. They are capable of switching packets between devices connected to the switch. A table is built in the switch based on the physical MAC address of the connected devices. A Layer 2 switch does not examine IP packets.

Layer 3 Switch - Layer 3 functionality of the 3rd layer of the ISO model. They examine network packets and make switching and routing decisions based on information in the Ethernet packets. They are used in networked audio and video network delivery systems and large or complex internetworks, such as the Internet. Layer 3 switches support packet routing, VLANs and IGMP-snooping and multicast data stream delivery.

LBC - Laptop Breakout Cable. The Extron cable that connects a computer laptop to an Extron computer-video interface.

LCD - Liquid Crystal Display. A panel that utilizes two transparent sheets of polarizing material with a liquid containing rod-shaped crystals between them. When a current is applied to specific pixel-like areas, those crystals align to create dark images. The dark areas are combined with light areas to create text and images on the panel. LCD panels do not emit light but are often back-lit or side-lit for better viewing.

LCD projector - Utilizing LCD panel technology, these projectors separate the red, green, and blue information to three different LCD panels. Since LCD panels do not produce color, the appropriate colored light is then passed through each panel and combined to exit through the projector lens and onto a viewing screen.

LCoS - Liquid Crystal on Silicon. This is a reflective display technology where one glass substrate is attached to a silicon chip which is coated with crystals. The chip contains the control circuitry.

LED Displays - Light Emitting Diodes, similar to those widely used for room lighting, are used to provide the light that shines through an LCD panel to collectively deliver a picture. LCD TVs that use LED backlighting are often referred to as “LED TVs.”

Lenticular screen - A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles. It must be held very flat to avoid hot spots. A large series of parallel lenticulations cut vertically into the screen surface to improve horizontal dispersion.

Level - The relative intensity of an audio or video source.

Level control - The level control on some interface products is similar to the contrast control on a data monitor. It can either increase or decrease the output signal level from the interface to a data monitor or projector. This results in greater or less contrast in the picture.

Light - The region of the electromagnetic spectrum that can be perceived by human vision, also known as the visible spectrum, which covers the wavelength range between about 0.4 µm to 0.7 µm. In laser and optical communications, this term denotes a broader portion of the electromagnetic spectrum, from the near-ultraviolet region of approximately 0.3 µm, through the visible region, and into the infrared region to 30 µm.

Light Emitting Diode – LED - A semiconductor device that emits incoherent, narrow-spectrum light within the p-n junction.

Light level - The intensity of a given lighting situation as measured in foot-candles (Ft-c).

Light source - In fiber optics, a generic for the optical signal transmitter in an optical loss test set - OLTS.

Lightguide - Also known as an optical waveguide or optical fiber, a glass or plastic fiber with the ability to guide light along its axis. It comprises a core at the center, surrounded by a cladding with a lower refractive index to keep the light within the core through total internal reflection.

Limiter - Audio circuit or device that prevents the signal from reaching a level where audible distortion can occur.

Line driver - A signal amplifier used to extend a video signal over extended distances. Similar in function to a distribution amplifier (DA), with one input and one output

Line level - Audio signal industry-referenced at 600 ohms, 0 dB. Consumer systems may use a different reference.

Line out - Audio output. In consumer systems, this may be 10,000-50,000 ohms, at -10 dB or -20 dB.

Line voltage - Alternating current (AC) at the level typically found in the home.

Linearity - The ability of a display device to produce an object the same size anywhere on the screen. For example, poor linearity may show the same line of text one size when it is at the top of the screen but a different size when it is at the bottom of the screen.

Link - An optical cable with connectors attached to the transmitter and receiver.

LinkLicense - License key that unlocks additional and/or enhanced features within an Extron product.

Lip Sync - A technical term for matching lip movements seen in a video picture with voice. Audio and video is synchronised when lip sync is maintained.

Listening plane - In acoustics, the intersection of the audio field (the horizontal plane) with the listener’s ear.

Logarithm - An exponent used in mathematical equations to express the level of a variable quantity (or, the power to which a number must be raised to produce a specific result).

Loop-through - A feature that allows the video signal to be passed through a device relatively unprocessed and sent to a local monitor or other device. The loop-through is separate from the circuits that process a signal for output to the main presentation or recording device(s). Loop-through connections are found on some scan converters and scalers. (Loop-out)

Loose buffer cable - A type of fiber optic cable in which the fiber is encased within a loosely surrounded buffer tube underneath the jacketing. The tube is usually for protection in outdoor installations.

Loose Tube Gel Filled – LTGF - A Loose Buffer Cable that is filled with a insulating gel material.

Loss - In fiber optics, the loss of optical power in connectors, splices, and fiber defects as light passes through a fiber optic system.

Loss Budget - A specified, maximum tolerable loss of optical power, or attenuation of light, as it passes through a fiber optic system.

Lossless - When using compression to reduce text and/or graphic files, some techniques discard data in the process. Methods that compress files without losing data are called lossless.

Lossy - A term to describe compression techniques that throw away data as part of the process. The more data loss, the smaller the file, and the lower the quality (grainy or jagged edged) of the image. Lossy compression methods include JPEG and MPEG. Note: with JPEG, high means high compression (greater loss) and low means low compression (less loss).

Lossy Compression - Method which discards (loses) some of the data, in order to achieve its goal, with the result that decompressing the data yields content that is different from the original, though similar enough to be useful in some way.

Loudness - The sound pressure level (SPL) of a standard sound. Loudness is the perception of the strength or weakness of a sound wave resulting from the amount of sound pressure level produced. Sound waves that have more intensity or larger variations in air pressure produce louder sounds. Low-intensity sound waves with smaller fluctuations in air pressure produce quieter sounds.

Loudspeaker - An electro-acoustic transducer that converts electrical audio signals at its input to audible sound waves at its output.

Low impedance - The condition where the source or load is at a lower impedance than the characteristic impedance of the cable. Low source impedance is common; low load impedance is usually a fault condition. Example: 30-600 ohms.

Low pass filter - A circuit that discriminates between low frequencies and high frequencies and allows only the low frequencies to pass. For example, a low pass filter design for a subwoofer, set at 80 Hz, would allow the audio signals below 80 Hz to pass through to the speaker, and attenuate the portion of the signal above 80Hz.

LPAC - Lossless Predictive Audio Compression. An improved lossless audio compression algorithm developed by Tilman Liebchen, Marcus Purat and Peter Noll at Institute for Telecommunications, Technical University Berlin (TU Berlin), to compress PCM audio in a lossless manner, unlike conventional audio compression algorithms which are lossy. It is no longer developed because an advanced version of it has become an official standard under the name of MPEG-4 Audio Lossless Coding.

LPCM - Linear PCM - A specific method of pulse code modulation that is used to represent an analog waveform as a sequence of amplitude values. LPCM has been defined as part of the DVD and Blu-ray Disc standards, and is also used by HDMI. Also see "PCM – Pulse Code Modulation."

LSFOH - Low Smoke and Fumes Zero Halogen. IEC designation of a cable jacket that passed IEC 332-3 flame test, IEC 61034 smoke test, and IEC 754-1 corrosivity test.

Lucent Connector – LC - A high-density optical fiber connector becoming more popular and are replacing the popular SC due to the smaller size. LCs are used on Extron fiber optic products.

Luma - Also called Luminance. The photometric radiance of a light source. The luma signal represents brightness in a video picture. Luma is any value between black and white and is abbreviated as “Y.” Also see "Chroma."

Luma (luminance) key - A picture-combining effect where the Y (luminance) portion of one video signal is replaced with video from another source. Luma keys are typically used to insert white text into a color video image.

Luma delay - A video problem in which the intensity of an object or area is shifted slightly to the right of the color. The color occurs in the correct area of the displayed image, but the luma (intensity) starts later.

Lumen - The unit of measure for light coming out of a light source, such as a projector. CRT projectors usually use a 10% white window pattern for measurement purposes, while LCD and DLP projectors use a 100% white window (ANSI standard). Also see "ANSI lumen."

Luminance - 1) In physics, The light density coming out of a surface. This is the specification for measuring the brightness of a projection screen or a CRT monitors tube surface. The SI unit is cd/m2 (candles per square meter). It is also called nit in the US system and foot-lambert in the English system. 1 foot-lambert = 3.426 cd/m2. 2) In video technology, The measurement of the black to white value for a pixel.

Luminous flux - The total amount of light coming from a light source, measured in lumens.

LVDS - Low Voltage Differential Signal. A signal transmission standard developed for the connection of laptop computers to their local LCD displays. National Semiconductor is the manufacturer that is promoting this standard. SGI used LVDS on the 320 and 540 NT Visual Workstations for connection to their 1600SW series, 16 x 9 aspect ratio, LCD monitor.


M - Mega. A prefix for one million.

MAAP™ Mini AV Connectivity Modules - Compact mountable metal plates available in hundreds of models offering popular pass-through audio, video, phone, data, power, and control connectors. Active MAAP modules are also available for power, control, and long distance signal transmission. Along with mounting options for maximum flexibility in placing connectors and controls within reach, these interchangeable components fit together to create an attractive and completely customizable AV connectivity solution.

MAC - Media Access Control. The Media Access Control data communication protocol sub-layer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multi-point network, typically a local area network (LAN). Access to the media may be spread out over time, or as in Ethernet, a mechanism is developed which allows random access, but provides a method for reattempting use of the media if a collision is experienced.

MAC address - Media Access Control. A unique hardware number given to devices that connect to the Internet. When your computer or networking device (router, hub, interface, etc.) is connected to the Internet, a table (see “ARP”) relates the device’s IP address to its corresponding physical (MAC) address on the LAN. Also see "ARP."

Macrobending - A term that describes a macroscopic deviation of an optical fiber’s axis from a straight line due to bending, to the extent that optical loss occurs.

Magnetic deflection - A method of altering the path of an object (such as an electronic beam) with a magnetic field. CRTs have magnetic coils that carry currents that create magnetic fields that control the path of the electron beam. Also called Magnetic focus.

Magnetic focus - See "Magnetic deflection."

Main Cross-Connect – MC - The central portion of a facility's backbone cabling that provides connectivity between equipment rooms, entrance facilities, horizontal cross-connects, and intermediate cross-connects. It usually consists of a distribution of patch panel.

Main Distribution Frame – MDF - A signal distribution frame that connects lines from the outside and lines on the inside.

Matched-Clad Optical Fiber - A singlemode optical fiber with a cladding of uniform refractive index, favored for being less susceptible to bending and splice losses.

Mathematically Lossless Compression - Allows the exact original data to be reconstructed from the compressed data. Data compacting in mathematically lossless processes is between 2:1 and 3:1. The term lossless is in contrast to lossy compression, which only allows an approximation of the original data to be reconstructed in exchange for better compression rates.

Matrix - An electronic device that accepts and distributes video (and/or audio) signals selected from multiple inputs and multiple outputs. Also see "Matrix switcher."

Matrix mixer - Similar to a matrix switcher, but with additional signal processing features, such as equalization (EQ), compression, and level/gain controls on the inputs and outputs.

Matrix switcher - A means of selecting an input source and connecting it to one or more outputs. Like a regular switcher, but with multiple inputs and multiple outputs.

Matte white - A screen with a flat, dull surface for even reflection over wide viewing angles.

MAV - The Extron acronym for matrix audio/video (switcher).

MB - Megabyte. A megabyte is actually 1,048,576 bytes, or roughly 1 million bytes.

MBC - Monitor Breakout Cable. A cable used to view a computer signal on a local monitor or terminal while routing the same signal to a new source, such as a data projector or monitor. An MBC provides three connections in the form of a “Y” cable, a “T” cable, or through a buffer in an enclosure box.

MBC power connector - Some of the Extron MBC high resolution buffers require power. The miniature power plug attached to some MBC cables plugs into the MBC power jack on the interface.

Mbps - Megabits per second. One million bits per second; a unit of measurement for data transmission.

Mechanical splice - A splice between optical fibers accomplished by using a mechanical fixture and an index gel, rather than by thermal fusion.

Media player - A software application used for the playback of audio and video files.

MediaLink™ - Extron's MediaLink System is a family of easy-to-use and inexpensive products that work together to control A/V equipment in any small, one-projector classroom, boardroom, or auditorium.

Megapixel - In digital imaging devices, megapixels define the resolution range when the number of pixels is equal to or greater than 1 million pixels. For example, SXGA is 1280 x 1024, or 1,310,720 pixels. This could be called a 1.3-megapixel device.

Messenger wire - A wire that is used as the supporting element of a suspended aerial cable. This wire may be an integral part of, or external to the cable.

MFTA - Multi-Frequency Termination Adapter. A single termination device with selectable frequencies for different applications.

MHz - Megahertz. One million hertz (cycles per second). Video bandwidth is measured in megahertz.

Microbend - A localized defect in an optical fiber at the core-cladding boundary, caused by mechanical stress that results in sharp, microscopic curvatures in the fiber.

Microbending loss - Loss in an optical fiber due to sharp, microscopic curvatures, caused by imperfections in fiber coating, cabling, packaging, and installation, such as cinching fibers too tightly with a tie wrap.

Micron – μm - A micron, or a millionth (10-6) of a meter.

Mid-Entry - In fiber optics, the opening up of a fiber optic cable mid-span in order to access the fibers inside.

Mid-range - The range of audio frequencies, 250 Hz to 5000 Hz, to which the human ear is most sensitive. Mid-range frequencies give sound its energy.

Military tactical cable - Heavy-duty cable designed for rugged installations in adverse environments.

Milli - m. Abbreviation for one one-thousandth. Example: 1 ms = 1 millisecond or 1/1000 second.

MIMO - Multiple Input Multiple Output antenna technology. In 802.11n. This technology promises to deliver up to 8x coverage and up to 6x speed of current 802.11g networks.

Mini zipcord - A 2.5 mm diameter fiber optic cable with two jacketed fibers that can be separated.

MIPS - Million Instructions Per Second. The rate at which a computer executes instructions.

M-JPEG - Motion JPEG or M-JPEG video compression applies the discrete cosine transform to each video frame independently. No temporal compression is applied in MJPEG and no frame interdependence exists as with MPEG compression. Each video frame is encoded as though it is an MPEG I-frame. Editing and random access are easily facilitated in product designs applying MJPEG.

Modal bandwidth - In fiber optics, the bandwidth-length product, measured in MHz-km, of an optical fiber due to modal dispersion.

Modal dispersion - In fiber optics, the dispersion of a single optical pulse into various modes which arrive at the light receiving device at different times. This limits the performance of multimode optical fiber.

Mode - A path for light within an optical fiber. Singlemode fiber comprises a single path, while in multimode fiber, there are multiple light paths.

Mode Field Diameter – MFD - A measure of the spot size or beam width of light propagating in a singlemode optical fiber. Usually this is 20% larger than the diameter of the core.

Mode filter - A device that removes higher-order modes in multimode fiber.

Modem - Modulator/demodulator. A device that puts information on a carrier signal and transmits it over a (phone) network. The same device receives such signals and demodulates, or separates the information from the carrier. A modem connects computers with other communication devices through ordinary phone lines.

Modulation - The process of adding an information signal to a carrier frequency to allow it to be transmitted. Thus, the carrier is modulated by the information signal, as in a modem.

Moiré - A pattern resulting from a combination of other patterns. In video, this is usually an undesirable pattern caused by an unwanted signal interfering with the desired signal. This may appear as a wavy motion.

Momentary contact - A non-latching contact closure that lasts as long as it is held in place.

Momentary switch - A switch that returns to its normal circuit condition when the actuating force is removed.

Monitor - (1) A TV that receives a video signal directly from an external source, such as a VCR, camera, or separate TV tuner to produce a high-quality picture. (2) A video display used with closed circuit TV equipment. (3) A device used to display computer text and graphics.

Monitor/receiver - A TV having RF tuning circuits to receive broadcast signals for viewing.

Monochrome - One color, usually interpreted as black and white. In computer CRTs, it is any single color with black.

Monochrome composite output - Provides a monochrome video output with combined horizontal and vertical sync for composite video with all the shades of the computer’s monochrome, 8-, 16-, or 64-color display adapter card output signal.

Monochrome signal - A video signal having one color, usually a black and white signal, or sometimes the luma portion of a composite or component color signal.

MPEG - Moving Picture Experts Group. A standards committee under the auspices of the International Standards Organization working on algorithm standards that allow digital compression, storage and transmission of moving image information such as motion video, CD-quality audio, and control data at CD-ROM bandwidth. The MPEG algorithm provides inter-frame compression of video images and can have an effective compression rate of 100:1 to 200:1.

MPEG-2 - The second generation standard for video compression of audio and video applying the discrete cosine transform. The standard includes a combination of lossy video and audio compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth. Commonly used for digital television transmission, DVD, and other similar equipment.

MPEG-4 - A patented collection of methods defining compression of audio and visual (AV) digital data. Uses of MPEG-4 include compression of AV data for web (streaming media) and CD distribution, voice (telephone, videophone) and broadcast television applications. MPEG-4 absorbs many of the features of MPEG-1 and MPEG-2 and other related standards, adding new features such as (extended) VRML support for 3D rendering, object-oriented composite files (including audio, video and VRML objects), support for externally-specified Digital Rights Management and various types of interactivity.

MPLS - Multiprotocol Label Switching. A mechanism in high-performance telecommunications networks which directs and carries data from one network node to the next. MPLS makes it easy to create “virtual links” between distant nodes. It can encapsulate packets of various network protocols.

MTBF - Mean Time Between Failures. A basic measure of reliability for repairable items. It can be described as the number of hours that pass before a component, assembly, or system fails. Also (MTBR) Mean Time Between Repairs.

MTP - Extron’s acronym for the Mini Twisted Pair line of products

MTS - Multichannel Television Sound. One of the first stereo sound systems developed for television. MTS consists of two independent singles each carrying a discrete channel. One channel provides stereo sound by providing left/right channel difference signals relative to transmitted mono audio track. The second carrier carries the Secondary Audio Program (SAP) which is used for a second language or for Descriptive Video, a descriptive commentary for the vision impaired.

MTU (Maximum Transfer Unit) - Each network has a maximum transfer unit or MTU, the maximum size for an Ethernet frame payload. Typically the MTU for a network is 1500 bytes. Routers break up data segments into two or more segments if the MTU is smaller than the payload in an Ethernet frame.

Multicast - Multicast addressing is a network technology for the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once, creating copies only when the links to the multiple destinations split. A single stream is sent from the source to a group of recipients.

Multimode Fiber – MMF - An optical fiber that allows for the propagation of more than one mode or light path. It is commonly used with LED light sources for shorter distance links.

Multi-Pass Transform - Multi-pass transforms return to a data set to carry out a process. Multi-pass transforms are often capable of supporting greater compression ratios, but use a greater amount of time to process the data.

Multiple Termination Plug – MTP - A small form factor – SFF plug for multiple fibers.

Multipoint - When more than two locations are connected for a videoconference using a bridge. Usually multipoint switching is done by video-follow-audio, such that the person speaking is automatically seen by the other conference site(s).

Multi-Purpose Transform - A multi-purpose transform is capable of converting more than one type of input format. The PURE3 codec is a multi-purpose transform in respect to its ability to process both video and computer graphic inputs which are different with respect to resolutions, color space, and color information.

Multi-Rate SDI - the capability to support multiple SMPTE serial digital interface standards, including SMPTE 424M (2.97 Gbps 3G-SDI), SMPTE 292M (1.485 Gbps HD-SDI), and SMPTE 259M (270 Mbps SDI).

MUX - Short for multiplexer. A device that combine multiple signals for transmission over a single line. The signals are demultiplexed (DEMUX’d), or separated, at the receiving end.


NAB - National Association of Broadcasters, the body that sets standards for US broadcast stations.

Nanometer – nm - A nanometer, or one billionth (10-9) of a meter.

NAS - Network Attached Storage. One or more storage devices associated with a single server which exists as a node on a LAN (Local Area Network).

NAT - Network Address Translation. Method of concealing a set of host addresses on a private network behind a pool of public addresses. It allows conservation of registered IP addresses within private networks and simplifies IP address management tasks through a form of transparent routing, and increases network privacy by hiding internal IP addresses from external networks.

Native Resolution - Refers to the single fixed resolution of an LCD, plasma, or other fixed matrix display. An image said to match the native resolution of a display is one where pixels between the image source and display are perfectly aligned and require no additional scaling or other signal processing.

Near end - In videoconferencing, the party or group at the local end of the connection.

NEC - National Electrical Code. The National Electrical Code is the product and responsibility of the National Fire Protection Association (NFPA). The NEC covers the installation of electric conductors and equipment in public and private buildings and other premises, such as yards, parking lots, carnivals, etc. In general, the NEC is used in every state in the nation and provides safeguards of persons and property from hazards arising from the use of electricity.

Networking - Two or more devices (or people) communicating with each other and sharing resources.

NEXT - Near-End Crosstalk. A measure of interference between the conductors of a cable. A measure of the unwanted signal coupling from a transmitter at the near end (source end) into neighboring pairs measured at the near end. NEXT loss is expressed in decibels relative to the received signal level.

NFS - Network File System protocol. This protocol enables users to access remote data and files over a shared network, in the same way they are accessed locally.

NIC - Network Interface Card. A piece of hardware, usually a peripheral card, that interfaces a computer to a network.

Nit - A unit of measurement of luminance, or the intensity of visible light, where one nit is equal to one candela per square meter. Nits are used to describe the brightness of computer displays, such as LCD and CRT monitors.

Node - One specific point or connected location on a network (i.e., a client or print server).

Noise - Any unwanted signal that adversely affects the quality of the picture or sound.

Noise criteria - Abbreviated “NC”. An NC level is a standard that describes the relative loudness of a room or space, across a range of frequencies. The NC level illustrates the extent to which ambient noise interferes with speech intelligibility. NC should be considered for any project where excessive noise would be irritating to the users, especially where speech intelligibility is important.

Noise gate - An audio processing device that reduces background noise by muting a sound signal when it falls below a pre-determined level, and restores it when the level increases again. For example, in a board room where multiple microphones are installed, a noise gate may be used to mute the microphones of those not currently speaking, in order to eliminate disturbing background noise in the sound support system.

Noise reduction - Any technique for reducing the amount of undesired noise in an audio signal. A common technique is called “companding”, a circuit that combines a COMPressor and an exPANDer. The signal is compressed before recording (which maximizes the signal to noise ratio), then expanded during played back. As the signal is expanded, noise tends to be “pushed down,” resulting in a quieter signal.

Noise-canceling - A microphone designed to cancel ambient noise so that it will not be broadcast or recorded. The housing of the microphone allows noise to reach both sides of the diaphragm simultaneously, one side canceling the other out. A close speaking voice strikes the diaphragm on only one side, generating a stronger signal with less background noise.

Nominal level - The signal strength level at which a product is designed to operate for optimized performance. Most of the specifications are tested at the nominal level and all of the built-in signal meter reference levels (e.g. 0dB) are set at the nominal level. A device’s input nominal level should match the nominal level of the source device it is connected to, while the output nominal level of a device should match the nominal level of the destination device it is connected to. The most commonly used nominal levels for video and audio are: video, 1Vp-p (video with sync), 0.7Vp-p (video without sync), 0.3Vp-p (chroma); audio, +4dBu (1.23V, pro audio line level), -10dBV (316mV, consumer audio line level), -60dBV (1mV, mic level).

Non-blocking matrix switchers - These are true matrix switchers allowing any input to switch to any or all outputs. They have no switching limitations contingent on hardware or software. Extron builds only true matrix switchers with all switching paths available at all times; there is no blocking.

Non-composite video signal - A video signal that contains picture and blanking information only with no sync information.

Non-interlaced - Also called progressive scan. A method by which all the video scan lines are presented on the screen in one pass instead of two. Also see "Interlacing" and "Progressive scan."

Non-plenum - A cable that does not meet CMP or CL2P flame test requirements.

Non-segmented - A system of video recording that uses one head to scan one field of video onto the tape.

Normally closed contact - Relay or switch contacts that are closed when the relay is not activated.

Normally open contact - Relay or switch contacts that are open when the relay is not activated.

Notch filter - A circuit that effectively separates the NTSC black and white information from the color 3.58 MHz carrier signal. The name is based on the fact that the circuit takes a notch out of the frequency band.

NSCA - National Systems Contractors Association. The NSCA is an international trade association of companies specializing in audio, video, security/life safety, presentation, lighting, or other low-voltage systems. This association offers an annual expo.

NTP - Network Time Protocol. This protocol is used to synchronize the real-time clock in computers and other devices over the network and Internet to a reference clock

NTSC - The color video standard used in North America and some other parts of the world created by the National Television Standards Committee in the 1950s. A color signal must be compatible with black-and-white TV sets. NTSC utilizes an interlaced video signals, 525 lines of resolution with a refresh rate of 60 fields per second (60 Hz). Each frame is comprised of two fields of 262.5 lines each, running at an effective rate of 30 frames per second.

Numerical Aperture – NA - In fiber optics, the sine of the acceptance angle, a critically defined angle measurement from the center axis of the fiber. Incoming light must be directed below this angle in order to enter the core of the fiber and propagate along its length through total internal reflection.

Nyquist frequency - The highest frequency that can be reproduced accurately when a signal is digitally encoded at a given sample rate. Theoretically, the Nyquist frequency is half of the sampling rate. For example, when a digital recording uses a sampling rate of 44.1kHz, the Nyquist frequency is 22.050kHz. If a signal being sampled contains frequency components that are above the Nyquist limit, aliasing (stair-stepping) will be introduced in the digital representation of the signal unless those frequencies are filtered out prior to digital encoding.

NZDS - Non-Zero Dispersion Shifted fiber. A singlemode fiber with the zero-dispersion wavelength slightly beyond the spectral region for transmission in order to improve performance.


OCR - Optical Character Reader or Optical Character Recognition. Hardware and software that reads characters as images and converts them into text to be used in a computer.

Octave - A doubling or halving of a frequency. For example, 200 Hz is one octave higher than 100 Hz; 50 Hz is one octave lower.

Ohm - The unit of electrical resistance, transmitting a current of 1 amp when subjected to a potential difference of 1 volt. Represented by W or Z.

OLED - Organic Light Emitting Diode displays use organic compounds that light up when electrical current is applied. Millions of individual pixels in an OLED can be turned completely on or off to deliver pure black.

OPEX - Operating Expense. An ongoing cost for running a product, business, or system.

Optical Ethernet - An optical connection for delivering Ethernet packets. Ethernet signals have been traditionally interfaced on twisted pair cable. Optical Ethernet connections are used to preserve quality delivering the same signal over a greater distance or security concerns.

Optical Link - A single fiber optic signal path or point-to-point fiber optic connection between a transmitter and receiver, including connectors, fiber, splices, and other fiber optic components in the path.

Optical Loss Test Set – OLTS - Test equipment for singlemode or multimode optical fiber comprising a light source and a power meter, used to measure optical signal loss along the fiber and any connectors in between.

Optical Return Loss – ORL - A measure, in dB, of the amount of optical power reflected within a fiber optic pathway due to the fiber and optical components.

Optical Time Domain Reflectometer – OTDR - An instrument in fiber optics used to measure backscattered light in the detection of defects along a span of optical fiber.

Oscilloscope - A test device that allows measurement of electronic signals by displaying the waveform on a CRT screen.

OSI Model Open System Interconnection Reference Model - OSI Reference Model is a definition for layered communications and computer network protocol design. It was developed as part of the Open Systems Interconnection (OSI) initiative. The OSI model divides the network architecture into seven layers starting from the bottom up: Physical, Data Link, Network, Transport, Session, Presentation and Application Layers.

Out of Order Packet - In computer networking, the delivery of data packets in a different order from which they were sent. Video decoders must account for out of order packets which may be experienced.

Output Power - In fiber optics, this is the radiant power, expressed in watts.

Outside Plant – OSP - In a telecommunications network, this is the portion that is situated mainly outdoors. This includes patch panels, closure, pedestals, cabling, poles, towers, repeaters, and other equipment.

Overbooking - In the telecommunications industry, overbooking -- such as in the frame relay world -- means that a telephone company has sold access to too many customers which basically flood the telephone company’s lines, resulting in an inability for some customers to use what they purchased.

Overfilled Launch Condition – OFL - In fiber optics, a condition where the incoming light has a spot size and numerical aperture–NA larger than acceptable by the fiber. Typically associated with LED transmission and multimode cable.

Overhead - Any data which is transferred on a communication link which is in addition to the content or data that is delivered. In IP networks, overhead includes: addressing, control, routing, redundant, errorchecking and error concealment data.

Overscan - The result of the TV scan lines exceeding the boundaries of the display screen.


Packet - A block of data that is transmitted over a network in a packetswitched system. A packet is also referred to as a frame or datagram.

Packet jitter - The term jitter is used as a measure of the variability over time of the packet latency across a network. In real-time applications such as VoIP and video, variation in the rate at which packets in a stream are received that can cause quality degradation. Video decoders must account for jitter which may be experienced delivering packets across a network.

Packet loss - Occurs when one or more packets of data traveling across a computer network fail to reach their destination. Packet loss is distinguished as one of the three main error types encountered in digital communications; the other two being bit error and spurious packets caused due to noise. Packet loss is typically experienced in the real world as a random burst of packet loss.

PAL - Phase Alternate Line. A television standard in which the phase of the color carrier is alternated from line to line. It takes four full pictures (8 fields) for the color-to-horizontal phase relationship to return to the reference point. This alternation helps cancel out phase errors. For this reason, the hue control is not needed on a PAL TV set. PAL, in many transmission forms, is widely used in Western Europe, Australia, Africa, the Middle East, and Micronesia. PAL uses 625-line, 50-field (25 fps) composite color transmission system.

PanelLink® - Silicon Image’s TMDS (Transition Minimized Differential Signaling) all-digital video transmission standard. PanelLink technology was designed to provide the bandwidth necessary to support digital displays.

Parametric equalizer - A type of audio equalizer having several “parameters” for control of various filters that can be applied to audio signals. Parametric equalizers are most widely used in situations where very fine control over the audio signal is desired, and provide control over gain, Q (Quality factor, a measure of a resonant system), and frequency. (See EQ-Audio)

Passive crossover - A crossover network that divides audio frequencies without any active amplification or buffering components and which uses only resistors, capacitors and inductors.

Passive Optical Network – PON - A fiber optic network comprising singlemode fiber, passive splitters, and passive couplers for a service provider to deliver fiber to the home – FTTH, or fiber to the building – FTTB.

Patch cord - A predetermined length of cable with connectors at both ends, also known as a cable assembly, patch cable, or jumper.

Patch panel - A passive device, typically flat plate holding feed-through connectors, that allows temporary circuit arrangements and rearrangements by simply plugging and unplugging patch cables. In fiber optics, this is also known as a cross-connect panel, and is used for interconnection of multiple cables or fibers.

PC - Personal Computer or Projector Control.

PCB - Printed Circuit Board.

PCM – Pulse Code Modulation - The digital representation of an analog audio signal. PCM is the standard form of digital audio in computers and the compact disc (CD) “red book” format, as well as the standard used for the audio portion of digital video recording.

PDF - Portable Document Format. A type of format developed by Adobe Systems with which the same file can be opened and viewed on most any computer platform (PC, Mac, Unix). It can also be printed on most any printer (dot matrix, laser, inkjet, PostScript, or non-PostScript). A PDF is a document file in that it includes text and graphics in one file that maintains the appearance of the original.

Peak - The highest level of signal strength, as determined by the height of the signal’s waveform.

Peak white - The whitest portion of a picture signal.

Peaking - A means of compensating for mid- and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. The higher the frequency and longer the cable length, the more peaking may be required.

Peaking control - Peaking control on Extron products compensates for mid- and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. When using the peaking control a noticeably sharper picture will be seen on all displays regardless of cable lengths. However, 100% peaking may provide over enhancement on short cable runs. Use the position that produces the sharpest image on the display screen. Also called “sharpness” control.

Peak-to-peak - Abbreviated “p-p.” The difference in amplitude (voltage, for example) between the most positive and the most negative excursions (peaks) of a signal.

Peripheral device - Normally an external device that a CPU communicates with, such as a printer, mouse, disk drive, or interface.

Persistence - In video, persistence is the staying power of a lighted phosphor, since a phosphor begins to dim after being excited by the electron beam. A long-persistence phosphor allows the screen to dim more slowly. Long-persistence phosphors are commonly used for CRT projection in 3D applications.

P-Frame - Predictive coded picture. Contains predictive information required to recreate a video frame.

Phantom power - A standardized method of providing power to condenser microphones using the two signal leads of a balanced audio connection. An international standard, IEC 60268-15, defines three DC voltages, 48 V, 24 V, and 12 V. In professional applications, 48 V Phantom power is the most common.

Phase - The relative timing of one signal to another, usually expressed in degrees of shift.

Phasing adjustment - To properly synchronize an NTSC/PAL video output signal to a genlock signal, a phasing adjustment to the horizontal phase and the subcarrier phase may be required. The horizontal phase difference between these two signals must be set to zero. Likewise, the subcarrier phase difference between these two signals must also be set to zero.

Phone plug - A small, round audio plug used as a speaker connector. Also called 1/4” phone plug.

Phono plug - A plug most often used with line level audio signals. Also known as an RCA plug.

Phosphor - The chemical coating on the inside of the CRT screen that emits light (monochrome or color) when struck by an electron beam. Each dot on the screen is actually a phosphor that glows for a period of time. Also see "Persistence."

Photodetector - A device that senses incoming light and outputs an electrical signal in response to the light.

Photon - A elementary unit of light with both waveform and particle properties.

Physical Contact – PC - In fiber optics, the point at which a glass surface, such as that of a fiber, physically touches another glass surface, usually that of a connector. PC polished connectors can be used with SPC or UPC polished connectors but are not compatible with APC polished connectors. Intermixing APC polished connectors with UPC/SPC/PC polished connectors can damage the fiber optic cable or equipment. Multimode applications always use PC, SPC, or UPC polished connectors.

Physical plant - Infrastructure components including cable, connectors, splices, panels, splitters, repeaters and regenerators necessary to propagate the light signal between the transmitters and receivers of a fiber optic system.

Picture tube - See "Cathode Ray Tube."

Pigtail - A short length of cable with one end terminated with a connector and the other end spliced or hard-wired to existing cable or equipment.

Pigtail assembly - A short length of fiber optic cable with one end terminated with a connector, and the other end fixed to a transmitter, receiver, or long length of cable via a splice.

Pin cushion - The inward or outward (curved) appearance of the edges of a display.

PIN Diode - Positive Intrinsic Diode. A type of photodiode, or optical signal transducer that converts light to an electrical signal, used in fiber optic receivers.

Pin out - An illustration or table that names signals, voltages, etc., that are on each pin of a connector or cable.

PIN-FET - Positive Intrinsic Negative Field Effect Transistor.

Ping - The Packet INternet Groper (ping) command is used to test connectivity between IP devices. The Internet Control Message Protocol (ICMP) echoes Ethernet packets to determine whether a network device is active and what the bidirectional delay is in communicating with it.

Pink noise - A type of random noise that contains an equal amount of energy per octave. The bands 100-200, 800-1600, and 3000-6000 all contain the same amount of energy. Since pink noise is based on octaves rather than individual frequencies, there is no increase in energy in the high octaves. Because of this, and because Real Time Analyzers (RTA) tend to look at octave or 1/3 octave ranges, pink noise is very useful for measuring the frequency response of audio equipment, as well as for determining room response for sound reinforcement applications.

PIP - Picture-in-Picture. A small picture within a larger picture created by scaling down one of the images to make it smaller. Each picture requires a separate video source such as a camera, VCR, or computer. Other forms of PIP displays include Picture-by-Picture (PBP) and Picture-with-Picture (PWP), which are commonly used with 16:9 aspect display devices. PBP and PWP image formats require a separate scaler for each video window.

Pitting - In fiber optics, an undesirable endface polishing condition resulting from the use of lapping film that has been contaminated with fiber optic and grit particles. Pitting can also denote small cracks in the endface due to exposure of cleaning agents to intense light through a fiber.

Pixel - Picture Element. The smallest unit or area of a video screen image that can be turned on or off, or varied in intensity.

Pixel clock - Dot clock. The pixel clock divides the incoming horizontal line of video into pixels. This pixel clock has to be stable (a very small amount of jitter) relative to the incoming video or the picture will not be stored correctly. The higher the frequency of the pixel clock, the more pixels that will appear across the screen (pixel resolution).

Pixel loss - A video problem in which picture information is missing, giving the appearance of specks in the image.

Pixel phase - An adjustment common to scalers and projectors, which adjusts the point in time that a sample is taken in the A-D conversion process. The pixel (or dot) clock in a computer and the pixel clock in a display device may operate at the same frequency for a given resolution and refresh rate, but not necessarily in phase with each other. Pixel phase adjustments are provided on digital monitors and projectors to synchronize the two independent clocks. A test generator like the Extron VTG 300 includes an alternating pixel pattern, which is used to eliminate banding and shimmering artifacts that are symptomatic of pixel phase error.

Pixel resolution - In computer graphics and video images, the number of pixels in the display. For example, a picture with 1,024 x 768 pixels is much sharper, or has higher resolution, than a picture with 640x480 pixels. The total number of pixels is the product of these two numbers.

Plane - In matrix switchers, a plane refers to all of the inputs and outputs of one signal. For example, the red plane would include all of the inputs and outputs for red signals; the blue plane would include all of the blue signals.

Plane breakaway - On matrix switchers, the ability to break one of the planes away from the others. Generally the video, sync, and audio planes will switch the same way (i.e., have the same switching pattern). With plane breakaway, an individual plane can be set up to switch independently of the others.

Plane grouping or I/O grouping - When a number of independent planes on a matrix switcher are all grouped so they switch in unison.

Plastic Optical Fibers - Optical fibers in which the core and cladding are made of plastic. The diameter of the core is often larger than that of glass fiber.

Plenum cable - Cable having a covering (jacket) that meets UL specifications for resistance to fire.

Plug - In A/V and fiber optics, this is also known as the male connector.

PLUGE - Picture Line Up Generation Equipment. This is the name of a test pattern that assists in properly setting picture black level. PLUGE can be part of many test patterns. The phrase and origination of the test signal are both credited to the British Broadcasting Company.

Plug-in - A program of data that enhances, or adds to, the operation of a parent program. Software decoders often use a plug-in provided in media players.

Point-to-point - A videoconference between two locations, like a telephone call. Also see "Multipoint."

Polarity - The positive and negative orientation of a signal. Polarity usually refers to the direction or a level with respect to a reference (e.g. positive sync polarity means that sync occurs when the signal is going in the positive direction).

Polishing paper - A plastic polishing sheet for optical fiber or connector endfaces with fine grit on one side.

Polishing puck - A fixture for optical fiber endface polishing, used to support a fiber optic connector ferrule in place, properly aligned to the lapping film.

Polyethylene - One of the Polyolefins used for Insulation of Non Plenum Wires and also in the Foaming form as Dielectric for all Non Plenum COAX.

Polyolefin - Family of Compounds consisting of Polyethylene , Polypropylene , PolyButylene etc.

Port - A connection for an input or output device. Typical ports found on a computer include serial, parallel, SCSI, disk drive, video, and keyboard ports.

Port Expansion - The process of assigning ownership of external control ports to a primary control processor.

Port number - A preassigned address within a server that provides a direct route from the application to the Transport layer or from the Transport layer to the application of a TCP/IP system.

Potentiometer - A variable resistor. Potentiometers typically have three terminals: the two end terminals, across which the entire resistance appears, and a third terminal, the “wiper”, which moves to a different spot on the resistor as the shaft is turned. In this manner, the resistance between the wiper and one end terminal gets smaller while, at the same time, the resistance between the wiper and the other end gets larger. This allows the potentiometer to be used as a variable voltage divider, for use in attenuators such as volume controls or tone controls.

PoE - Power over Ethernet. The delivery of power to a remote device using the same cable lines used to deliver Ethernet data. This enables a single cable to provide both data and power to devices.

Power (electrical) - The dissipation of heat by passing a current through a resistance. Measured in watts [W], Power [P] is expressed by ohm’s law from the three variables: voltage [E] current [I] and resistance [R]. That is, P = I2 x R, or, P = E2/R or P = E x I.

Power meter - A device that measures the loss of optical power in a fiber optic connector, fiber optic cable, or fiber optic system.

Powered Ethernet - A standard (IEEE 802.3af) that provides power to network devices by utilizing the existing Ethernet connection, thereby eliminating the need for additional, external power supplies.

Preamp - Preamplifier. An electronic circuit that raises a weak signal high enough to be fed into an amplifier.

Presentation device - A general term used to define a video projector, plasma display, presentation monitor, or other large format data display device.

Primary colors - Any set of colors from which other colors can be derived. In video, the primary colors are red, green, and blue. Equal amounts of red, green, and blue make white; the absence of all colors makes black.

Private Network - A communication network owned by one or more firms for their exclusive use.

Pro Series Control Ports - Control Ports within an Extron product that may be added to an Extron Control Processor by means of Port Expansion.

Proc amp - See "Processing amplifier."

Processing amplifier - An electronic device that stabilizes, changes, or rebuilds signals.

Profile Alignment System – PAS - A technique for fusion splicing that employs a CCD camera for precisely aligning the cores of two optical fibers.

Progressive - A method for displaying, storing or transmitting moving images in which all the lines of each frame are drawn in sequence.

Progressive scan - A method by which all the video scan lines are presented on the screen in one pass instead of two. Typically denoted by the letter “p”, as in “480p”, which indicates a signal with 480 active lines running at 60 frames per second. Also see "Non-interlaced."

Projection - The process of presenting visual media by light transmitted through an optics system to a viewing screen.

PROM - Programmable Read Only Memory. An electronic memory that does not lose its contents when power is removed, and that can be reprogrammed using a special PROM programmer (“burner”). Also see "EEPROM" and "EPROM."

Pro-MPEG Forum - An association of broadcasters, program makers, equipment manufacturers, and component suppliers with interests in realizing the interoperability of professional television equipment, according to the implementation requirements of broadcasters and other end-users. The Forum has been in existence for approximately eight years and has over 130 members.

Propagation delay - The amount of time that passes between when a signal is transmitted and when it is received at the opposite end of a processor, amplifier, or cable.

Protocol - A set of agreed-upon standards that define the format, order, timing, handshaking, and error checking method for data transfer between two pieces of equipment.

Pseudorandom noise - A noise that satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a sequence of pulses that will usually repeat itself, albeit after a long time or a long sequence of pulses.

Public Network - A network established and operated by a telecommunications provider, for specific purpose of providing data transmission services for the public. The Internet is a public network.

Pulse broadening - An increase in the duration of a pulse.

Pulse code modulation - A method used to convert an analog signal into noise-free digital data that can be stored and manipulated by computer. PCM takes an 8-bit sample of a 4kHz bandwidth 8000 times a second, which gives 16K of data per second.

Pulse spreading - The dispersion of an optical signal as it traverses along an optical fiber. Also known as Pulse Dispersion.

Pulse width - The time during which a source, such as a laser, is in an “on” state.

Pulse width modulation - A powerful technique for controlling analog circuits with a processor’s digital outputs. PWM is employed in a wide variety of applications, including high power switching amplifiers. By controlling analog circuits digitally, system costs and power consumption can be drastically reduced.

PURE3 Codec - A codec which is capable of encoding and streaming both video and computer graphic inputs and a wide variety of resolutions, preserving equal quality for both signal formats. It preserves a balance between three performance factors low latency, low bandwidth and high image quality. The PURE3 Codec has been optimized for use on IP networks which are acknowledged to be lossy. The codec includes an error concealment system which is highly resistant to network errors without using forward error correction.

PVC - Poly Vinyl Chloride. Used for Insulation of Wires and Jacketing of most Non Plenum Cables.


Q-factor (Quality factor) - A measure of the “quality” of a resonant system. Resonant systems respond to frequencies close to the natural frequency much more strongly than they respond to other frequencies. On a graph of response versus frequency, the bandwidth is defined as the 3 dB change in level besides the center frequency.

QoS - Quality of service. Performance, such as transmission rates and error rates, of a communications channel or system. A suite of features that configure queuing and scheduling on the forwarding path of an E-Series router. QoS provides a level of predictability and control beyond the best-effort delivery that the router provides by default. (Best-effort service provides packet transmission with no assurance of reliability, delay, jitter, or throughput.). Also see "CoS."

QS-FPC™ - QuickSwitch Front Panel Controller. This is a front panel controller on Extron matrix switchers. The panel allows easy set up and control of the matrix switchers through a series of buttons on the front panel.

Quad standard - A term used for video products that are compatible with the following four standards: NTSC 3.58, NTSC 4.43, SECAM, and PAL.

Quantum Dots - Also known as “QD” “or “Nano Crystals,” Quantum Dots are specialized materials that are applied to or over an LED to precisely fine-tune the color output for a wider range of more accurate color. Some brands use “QLED” to describe a system with LCD, LED, and Quantum Dot technology.

Quantization - The process of sampling an analog signal to convert its values into digital data.

Quantizing error - Inaccuracies in the digital representation of an analog signal. These errors occur as a result of limitations in the resolution of the digitizing process.

Quantizing noise - The noise (deviation of a signal from its original or correct value) that results from the quantization process. In serial digital video, it is a granular type of noise that occurs only in the presence of a signal.

QUXGA - Quad UXGA, a computer resolution of 3200 x 2400 pixels (four times 1600 x 1200)

QXGA - Quantum extended graphics array. A graphics standard with 2048 x 1536 pixels.


Rack unit - As defined by the Electronics Industries Association (EIA). In reference to product rack height, a unit is a universal measurement: 1.75 inches or 44 mm. 1U (Unit) high refers to 1.75 inches, 2U high refers to 3.5 inches, etc.

RAM - Random Access Memory. RAM is volatile memory that can be written to and read from. RAM is the working memory where active programs and data are stored. RAM normally loses its contents when power is removed. Also see "PROM."

Random Error - Errors in measurement that lead to measured values being inconsistent when repeated measures of a constant attribute or quantity are taken.

Random noise - Also known as “white noise.” A noise signal that never repeats and has a flat frequency spectrum. Random noise can also be a digital pattern that never repeats. Random noise is generally considered to have a Gaussian amplitude distribution, but numerically generated noise can also have a flat amplitude distribution. The amplitude of random noise is normally measured as the rms value.

Raster - A raster is the series of scan lines that make up a TV picture or a computer’s display. The term raster line is the same as scan line. All of the scan lines that make up a frame of video form a raster. Lines and rows of dots such as those on the illuminated face of a video screen. A matrix of pixels or the scan lines on a CRT.

RC network - An electrical network that is constructed using a resistor and capacitor in parallel, and acts as an effective high-pass filter.

RCA plug - A connector type most often used with line level audio signals and composite video. (Phono)

Real Images - Are collected from the real world through image sensors. Video collected from film or electronic cameras can be considered real images.

Real-time - A system is said to be real-time if the operation delivers a correct value in the time and frequency in which it is required. The video system applied in North America, NTSC requires a real-time system capable of delivering 30 frames per second.

Real-time analyzer - A device that measures room acoustics in real time, typically using pink noise. Also see "Pink noise."

Rear projection screen - A translucent screen with a special coating that allows an image to be projected through the screen from the rear, instead of from the front. Also see "Front projection screen."

Rear screen projection - A presentation method in which the image is projected through a translucent screen toward the audience.

Rec. 2020 - See "BT.2020."

Rec. 709 - See "BT.709."

Receive – Rx - In fiber optics, to detect an optical signal from a fiber optic cable using a photodetector, such as a PIN diode, APD, or PIN-FET, and convert it to an electrical signal. The receive port of a transceiver.

Receiver - In fiber optics, this is the device at the receiving end of a fiber optic system that converts an optical signal to an electrical signal, and houses the necessary signal processing to output telecommunications, data, or A/V signals.

Receiver sensitivity - The minimum optical power necessary for the photodetector in a receiver to achieve a specified BER - Bit Error Rate or other performance specification such as signal-to-noise ratio.

Reclocking - Reclocking is a process that is used to restore the amplitude, rise and fall times, and clock rate attributes of a digital signal. Reclocking can add a small amount of time delay to the signal.

Reconstruction filter - A lowpass filter used to reduce aliasing and to soften the digital edges in an image. Without the reconstruction filter, images may have a Moiré pattern. On Extron products, this feature, referred to as Filter Mode, is selected to be either “ON” or “OFF.” The Filter Mode is intended for use with digital projectors. The feature should, however, be turned off when using CRT displays.

Redundancy - Repeated data or equipment which provides a backup if the primary data or equipment fails.

Reflectance - In fiber optics, the ratio of optical power reflected to the incident power at a connector junction or other component or device. It is expressed as a negative value in decibels – dB.

Reflections - With video signals, reflections can be caused by energy that is not absorbed by the load (or a termination) and is reflected and possibly combined with the original signal. Reflected signals can occur when the impedance does not match (as a result of wrong termination or mixing of cable impedance). Some of the undesirable results of reflection include Y/C delays, color smearing, ringing on luma (but not on color), and ghosts. In fiber optics, abrupt changes in the direction of light at an interface between two dissimilar media so that the light returns to its origin.

Refraction - The change in direction of light as it passes from one medium to another, dissimilar medium. Refraction also occurs as light passes through a graded-index medium in which the refractive index varies within the medium.

Refractive index - Also known as the Index of Refraction, the ratio of the speed of light in a vacuum to the speed of light in a material.

Refresh rate - Also called “Vertical Scan Frequency” or “Vertical Scan Rate”. The number of times in a second that display hardware draws a new video frame.

Relay - A device that acts like a switch and is controlled by a current. The relay switch contacts and then controls another circuit to pass a signal. Most relays are either solid state or electromagnetic.

Remote control - A wired or wireless device for controlling the function of another device at a distance. Also see "Infrared Remote."

Repeater - See "HDCP – High-bandwidth Digital Content Protection."

Repeater/Regenerator - A repeater is a device that detects a weak signal and boosts its power for continued transmission. A regenerator receives a signal and regenerates or reconstructs its waveform for transmission.

Resistance - The opposition to the flow of electric current. Also see "Ohm" and "Power (electrical)."

Resistor - An electrical component that limits the flow of current via resistance or impedance. It allows a specific amount of current to flow, as determined by the voltage applied to the resistor.

Resolution - The density of lines or dots that make up an image. Resolution determines the detail and quality in the image. A measure of the ability of a camera or video system to reproduce detail, or the amount of detail that can be seen in an image. Resolution is often expressed as a number of pixels, but more correctly, it is the bandwidth. A sharp, clear picture has high resolution. Also see "Resolution (horizontal)" and "Resolution (vertical)."

Resolution (horizontal) - The amount of detail in a horizontal direction in a video image. It is expressed as the number of distinct vertical lines, alternately black and white, that can be seen in the width of the picture. This information is usually derived from observation of the vertical wedge of the test pattern. Horizontal resolution depends on the high frequency amplitude and phase response of the pick-up equipment, as well as the transmission medium and the monitor itself.

Resolution (vertical) - The amount of resolvable detail in a vertical direction in a video image. It is expressed as the number of distinct horizontal lines, alternately black and white, that can be seen in a test pattern. Vertical resolution is primarily determined by the number of horizontal scanning lines in a frame.

Resonance - (1) Electronically, the condition where the inductive reactance and capacitive reactance are equal. (2) Acoustically, an intense and prolonged sound produced by a sympathetic vibration.

Retrace - During the scanning of a picture onto a screen, scan lines are produced from left to right. Before scanning the next line, the electron beam must get back to the left side of the screen. This is called retrace. The beam must be turned off (blanked) during retrace time. (See “Horizontal blanking” and “Vertical blanking.”) A retrace problem could appear as missing video information on the left side of the screen. Also see "Horizontal blanking" and "Vertical blanking."

Retrace time - The time required to move the scanning beam from the right side to the left side of the screen.

Retro - A rear-projection video display.

Return loss - A measure of reflected energy in decibels at a specific frequency and cable length.

Reverberation - The persistence of sound in an enclosed space, as a result of multiple reflections after the sound source has stopped. The decaying residual signal that remains after a sound occurs, created by multiple reflections as the original sound wave bounces off walls, furniture, and other non-absorbing barriers within a room or other acoustical environment. A room with very little reverberation is called a “dead” room, which is the opposite of a “live” acoustic space which is very reflective.

Reverberation time - The length of time required for the sound field to collapse, after the sound source has stopped.

RF - Radio frequency. A range of frequencies used for electromagnetic transmission (e.g., radio and TV).

RF adapter - A device that allows video and audio signals from a video tape recorder (VTR) or computer to be shown on a standard TV receiver. This device produces comparatively poor resolution and picture quality. Also called “RF converter.”

RF control - A medium of remote control from which signals are sent to the controlled equipment via data pulses modulated on an RF carrier signal.

RFI - Radio Frequency Interference. High frequency interference from transmissions such as telephones, microwaves, and television stations.

RG/U - Radio Guide/Universal. Military abbreviation for coaxial cable.

RGB - Red, Green, and Blue. The chroma information in a video signal. The basic components of the color television system. They are also the primary colors of light in the additive color process. Also see "Subtractive color process."

RGBHV - Red, Green, Blue, Horizontal, and Vertical Sync. A five-wire signal where the red, green, and blue video signals, as well as the horizontal and vertical sync signals, are on its own conductor.

RGBS - The Red, Green, and Blue chroma information in a video signal, with a separate channel for the sync signal.

RGsB - Red, Green, Blue, and Sync on Green. A three-wire signal with separate red, green, and blue video signals with the sync (horizontal and vertical) on the green signal.

Ribbon cable - A cable with several copper wires or optical fibers, each jacketed side-by-side in a flat, ribbon-like structure.

Ribbon splice - The splicing of individual optical fibers of a ribbon cable, with each fiber spliced on a groove of a substrate or etched silicon chip. Each groove is spaced evenly and a flat cover holds the fibers in place on the substrate.

Ripcord - A cord of strong yarn, situated under the cable jacketing, used to facilitate in stripping and removal of the jacket.

Ripple - Generally referring to the wavelike variations in the amplitude response of a filter.

Rise time - The time required for a signal to go from 10% to 90% of its maximum amplitude level.

Riser - A type of cable designed for vertical runs in shafts spanning multiple floors in a building.

RJ - Registered Jack. A type of modular jack that is similar to those used with telephones. Examples: RJ-11 = 4 or 6 wire module, RJ-45 = 8-wire module.

RJ-45 - Registered Jack-45. A connector similar to a telephone connector that holds up to eight wires, used for connecting Ethernet devices.

RMII - Reduced Media Independent Interface. A standard developed to reduce the number of signals required to connect a PHY to a MAC.

rms - An acronym for “root mean square.” Used in audio to help rate the continuous power output of an amplifier or input capability of speakers. This is the preferred method for comparing anything in audio applications.

ROM - Read Only Memory. Permanent memory that can only be loaded once, normally by the manufacturer. Contents may not be altered or removed. Also see "EEPROM", "EPROM", and "PROM."

Room mode - An acoustical resonance in a room caused by parallel wall surfaces. Any set of parallel walls will establish a series of standing waves, the lowest one of which has the wall spacing as a half-wavelength. These sound waves interfere with one another to produce a series of places where the SPL is high and another series of places between then where the SPL is very low. It is as if the sound wave were stationary between the two surfaces.

Rooming - With large matrix switching systems, such as the Extron Matrix 3200/6400 Series Switchers, specific outputs can be assigned to a room. That room sees only those outputs, even though they are part of a total switching system. The outputs seen by a room have virtual numbers (may be different from the physical numbers). Room presets using those outputs can be saved and recalled without affecting other switcher outputs.

Router - A network device that forwards packets from one network to another. Routing is a layer 3 function. Routers forward packets based on programmed or “learned” routing tables. Each incoming network packet is examined and a decision is made where to forward it. The destination address in the packets determines which port outgoing packets are directed to. In large-scale enterprise routers, the current traffic load, congestion, line costs and other factors determine which line to forward to.

RS-170A - EIA technical standard for NTSC color TV. A video standard that ensures proper synchronization of video signals and components.

RS-232 - An Electronic Industries Association (EIA) serial digital interface standard specifying the characteristics of the communication path between two devices using either DB-9 or DB-25 connectors. This standard is used for relatively short-range communications and does not specify balanced control lines. RS-232 is a serial control standard with a set number of conductors, data rate, word length, and type of connector to be used. The standard specifies component connection standards with regard to the computer interface. It is also called RS-232-C, which is the third version of the RS-232 standard, and is functionally identical to the CCITT V.24 standard.

RS-330 - An EIA technical standard that provides details for industrial closed-circuit television (CCTV).

RS-343A - An EIA standard for high resolution monochrome CCTV.

RS-422 - An EIA serial digital interface standard that specifies the electrical characteristics of balanced (differential) voltage, digital interface circuits. This standard is usable over longer distances than RS-232. This signal governs the asynchronous transmission of computer data at speeds of up to 920,000 bits per second.

RS-485 - An EIA standard for multipoint communications. It is similar to RS-422, but can support several nodes per line because it uses lower impedance drivers and receivers and allows for addressing.

RTCP - Real Time Control Transport Protocol – Provides out-of-band statistics for an RTP session

RTMP - Real Time Messaging Protocol – Data transfer protocol for high-performance transmission of audio, video, and data from an encoder to a server for distribution across a network.

RTMPS - Real Time Messaging Protocol Secure – Secure version of RTMP that encrypts the stream between the encoder and the CDN (Content Delivery Network), and provides protection against domain impersonation.

RTP - Real-time Transport Protocol, an IETF standard for streaming realtime multimedia over IP in packets.

RTSP - Real Time Streaming Protocol. A network control protocol designed for use in entertainment and communications systems to control streaming media servers.

Run length encoding - Simple form of data compression in which runs of data are stored as a single data value and count, rather than as the original run. This is most useful on data that contains many such runs: for example, relatively simple graphic images such as icons, line drawings, and animations.


S/N ratio - See "Signal to Noise ratio."

S/PDIF – Sony/Philips Digital Interconnect Format - A data protocol for compressed or uncompressed digital audio co-developed by Sony and Philips Electronics and now part of the larger AES/EBU audio standard. S/PDIF is often misconstrued as a connection type; however, S/PDIF audio can be found in products using either a 75 ohm coaxial connection or a TOSLINK fiber optic connection. S/PDIF is commonly found in Compact Disc and DVD players.

SACD – Super Audio Compact Disc - A very high fidelity, read-only optical disc format for both two-channel stereo and 5.0 (no sub-woofer) or 5.1 surround sound audio. SACD can store up to 10 times as much data as a standard audio CD, up to 7.95 GB. Support for SACD audio was added to the HDMI 1.2 specification in 2005.

Sag - A measure of the amount of sag in a fiber optic cable, taken at the midpoint of a span of cable between two points of support.

Sag section - A section defining a span of fiber optic cable between two points of support.

Sag span - A span selected within a sag section, used as a control to determine the proper sag, and therefore, tension of a fiber optic cable. At least two, and normally three sag spans in a sag section are required to sag a section properly.

Sag tension - The tension at which a fiber optic cable is designed to be installed.

Sample rate - The rate at which an analog signal is sampled. It is frequently expressed as kilosamples/sec (kS/s) or Megasamples/sec (MS/s. For example, 44.1 kHz is the standard sample rate for compact disks; 48 kHz is often used with digital audio tape (DAT) recording. A higher sample rate allows a higher frequency response. In order to accurately reconstruct a sound, the sample rate must be at least twice the highest frequency in the sound.

SAP - Second Audio Program. A feature of MTS television stereo audio, SAP permits the delivery of a second soundtrack for enhanced services such as second language or descriptive video services (DVS) for the vision impaired.

SAP - Session Announcement Protocol – Protocol using SDP (Session Description Protocol) for advertising multicast session information that provides multicast session names and correlates the names with the multicast traffic.  Used predominantly in support of streaming, VoIP, and Video Conferencing applications

Saturation - Chroma, chroma gain. The intensity of the color, or the extent to which a given color in any image is free from white. The less white in a color, the truer the color or the greater its saturation. On a display device, the color control adjusts the saturation. Not to be confused with the brightness, saturation is the amount of pigment in a color, and not the intensity. Low saturation is like adding white to the color. For example, a low-saturated red looks pink.

SC - Subcarrier. The modulation sidebands of the color subcarrier containing the R-Y and B-Y information. A secondary signal containing additional information that is added to a main signal.

SC/H phase - Subcarrier to Horizontal phase. In NTSC video, this is the phase relationship of the subcarrier to the leading edge of horizontal sync. SC/H phase is correct when the zero crossing of subcarrier is aligned with the 50% point of the leading edge of sync. In PAL video, the SC/H phase is defined as the phase of the EU component of the color burst extrapolated to the half amplitude point of the leading edge of the synchronizing pulse of line 1 of field 1.

Scalability - The property of a system, a network, or a process, which indicates its ability to handle growing amounts of work in a graceful manner with a limit which is unlikely to be encountered.

Scaler - A device for converting video signals from one resolution or framerate to another: usually upscaling or upconverting a video signal from a low resolution (e.g. standard definition) to one of higher resolution (e.g. high definition television).

Scaling - A conversion of a video or computer graphic signal from a starting resolution to a new resolution. Scaling from one resolution to another is typically done to optimize the signal for input to an image processor, transmission path or to improve its quality when presented on a particular display.

Scan - (1) In video, to move an electron beam across the raster in a camera or monitor. (2) To feed visual information into a computer by means of an optical device called a scanner.

Scan converter - Also called “video converter” or “TV converter,” a scan converter is a device that changes the scan rate of a source video signal to fit the needs of a display device. Examples: computer-video to NTSC (TV), or NTSC to computer-video.

Scan doubler - A device used to change composite interlaced video to non-interlaced component video, thereby increasing brightness and picture quality. Also called “line doubler.”

Scan-doubling - The process of making the scan lines less visible by doubling the number of lines and filling in the blank spaces. Also called “line-doubling.”

Scattering - A source of optical signal loss in a fiber optic system, caused by the scattering of light due to small particles and other imperfections in the fiber.

Scribe - Scratching the surface of the fiber so that it can be precisely and cleanly cut at a right angle to the fiber axis.

Scribe tool - A device consisting of a scribing blade, usually made from diamond or tungsten carbide, used to scribe, or score a fiber to allow for a clean break and a smooth endface.

Scrolling - The displayed image (or interfering noise on the image) rolling constantly on the screen.

SCSI - Small Computer System Interface. Pronounced “skuzzy.” An industry-standard input/output bus for peripheral computer devices, such as hard disks and CD-ROM drives. A standard peripheral bus on Mac computers. Improvements, such as the number of data lines and speed, have been made to the original SCSI to become SCSI-2 and SCSI-3.

SDH - Synchronous Digital Hierarchy. Also see "SONET."

SDI - Serial Digital Interface. Standard definition video is carried on this 270 Mbps data transfer rate. Video pixels are characterized with a 10-bit depth and 4:2:2 color quantization. Ancillary data is included on this interface and typically includes audio or other metadata. Up to sixteen audio channels can be transmitted. Audio is organised into blocks of 4 stereo pairs.

SDP - Session Description Protocol – Format used for describing multimedia communication sessions for the purposes of session announcement and session invitation.  Used predominantly in support of streaming, VoIP, and Video Conferencing applications.

SDSL - Symmetrical Digital Subscriber Line. Offers bandwidth of up to 2.3Mbps upstream and downstream over a single twisted pair copper phone line, over distances up to about 10,000 feet on an unrepeatered basis.

SDTV - Standard digital television. A serial digital format whose samples and timing are derived from 4:2:2 digital component video sources. The main difference between existing digital component video and SDTV is an MPEG-2 compression step to reduce the channel bandwidth.

Seamless switching - A feature found on many Extron video switchers. This feature causes the switcher to wait until the vertical interval to switch. This avoids a glitch (temporary scrambling) which normally is seen when switching between sources.

SECAM - Sequential Couleur Avec Mémoire, or “sequential color with memory.” A composite color transmission system that potentially eliminates a need for both a color and hue control on the monitor. One of the color difference signals is transmitted on one line and the second is transmitted on the second line. Memory is required to obtain both color difference signals for color decoding. This system is used in France, North Africa, Russia, Saudi Arabia, and many Eastern European countries. It is similar to PAL but produces color signals in a different manner. SECAM uses 625 horizontal scan lines, 50 fields per second (625/50).

Secondary processors - Extron IP Link Pro secondary controllers used for port expansion when the system requires more ports than are available on the Primary Processor. The Secondary Processors do not run any python programs.

SED - Surface-conduction Electron-emitter Display. SED is a new type of flat-panel display technology developed by Canon and Toshiba. SED is capable of high levels of brightness and color performance, as well as a wide angle of visibility, that on a par with a CRT. Large screens can be produced by simply increasing the number of electron emitters in accordance with the required number of pixels.

Sensitivity - A standard way to rate audio devices like microphones, loudspeakers, and amplifiers. For loudspeakers, sensitivity is rated by applying 1 watt of power to the speaker and measuring sound pressure level (SPL) at one meter. For microphones, sensitivity is expressed as the minimum input signal required to produce a standard output level. For a power amplifier, sensitivity is rated as the input level required to produce 1 watt of power output into a specified load impedance, typically 4 ohms or 8 ohms.

Serial data - A way to transfer information by breaking the characters of a word into bits, which are then transmitted sequentially along a single line. Compare to parallel, which uses more than one line.

Serial port - An input/output connection on the computer that allows it to communicate with other devices in a serial fashion data bits flowing on a single pair of wires. The serial port is used with RS-232 protocol.

Serration pulse - A vertical synchronizing pulse divided into a number of small pulses, each acting for the duration of half a line in a television system. Serration pulses are used to keep the horizontal oscillator synchronized during the vertical sync pulse interval.

Service loop - A deliberately allotted slack of fiber optic cable, in a splice tray, closure, vault, or communications output, to accommodate future needs.

SFP - Small form-factor pluggable. The SFP is an interface used in fiber optic connections for direct signal connections or packet switched networks.

SFTP - Secure File Transfer Protocol. It is a network protocol extension of SSHF using certificates and encryption for secure file transfer.

Shadow mask - A metal plate with holes or vertical lines that is used to determine exactly where the electron beam strikes the CRT screen.

Sharpness - The definition of the edges of an image. Also see "Peaking."

Sharpness control - Same as Peaking control.

Sheath - Also known as a cable jacket, the outer protective covering of wire or fiber optic cable.

ShiftLock™ - An Extron feature used to lock video displays together when using Extron VideoShift™, synchronizing the movement of their images.

Signal loss - A video problem that shows up as a faint picture for lack of video information.

Signal Noise - A random fluctuation in an electrical signal, a characteristic of all electronic circuits.

Signal to Noise ratio - Also stated as "S/N ratio". The ratio is expressed in decibels as a ratio between the audio or video signal level and that of the noise accompanying the signal. The higher the S/N ratio, the better the quality of the sound or picture.

Simplex cable - A cable comprising a single optical fiber.

Single Pass Transform - Transformation process which is carried out making only one examination of a data set. A single pass transform is required to maintain a low delay.

Single-ended - An unbalanced circuit where one side of the circuit or transmission line is grounded. Single-ended audio is unbalanced audio.

Single-Link DVI - The electrical signaling used to transmit data over DVI is known as transition minimized differential signaling, or TMDS. A single TMDS link carries three data channels and one clock signal, with a maximum video frequency of 165MHz, capable of standard resolutions up to 1920x 1200 pixels. See also “Dual-Link DVI.” Also see "Dual-Link DVI."

Single-Link HD-SDI - See "SMPTE 292M."

Singlemode Fiber – SMF - An optical fiber with a small core, through which only a single mode can propagate.

Sink - See "HDCP – High-bandwidth Digital Content Protection."

SIS™ also allows control over IP - Simple Instruction Set.™ A set of commands developed by Extron that allows easy RS-232 control of certain Extron products with a minimal number of characters in the commands and responses.

Skew - Refers to the timing difference which occurs when electrical signals which are traveling over different pairs of cables reach their destinations at different times. The different arrival times of the signals may present a problem when simultaneous arrival with no delay is required.

Skew-Free - A reference to special twisted pair cable in which the length differences between cables reduced to a minimum, thus reducing cable skew.

SL - The Extron product designation for ShiftLock.

SLA - Service Level Agreement. An agreement between a network service provider and the user, defining an established a set of metrics to measure the service delivered relative to the service delivered. A SLA typically identifies the bandwidth delivered, Quality of Service and service response time.

Slew rate - The ability of audio equipment to reproduce fast changes in amplitude. Measured in volts per microsecond, this specification is most commonly associated with amplifiers, but applies to most types of audio products. In amplifiers, a low slew rate “softens” the attack of a signal, “smearing” the transients and sounding “mushy.” Since high frequencies change in amplitude the fastest, this is where slew rate is most critical. An amp with a higher slew rate will sound “tighter” and more dynamic.

Smearing - A video problem where objects such as horizontal bars extend past their boundaries. Also called “over-peaking.”

SMPTE - Society of Motion Picture and Television Engineers. A global organization, based in the United States, that sets standards for baseband visual communications. This includes film as well as video and television standards.

SMPTE 259M - Defines the SDI serial digital interface common to most standard definition digital video products. SMPTE 259M includes several data rates, including 143 Mbps (NTSC composite digital), 177 Mbps (PAL composite digital), 270 Mpbs (4:2:2 component digital, 4:3 standard video aspect), and 360 Mbps (4:2:2 component digital, 16:9 widescreen video aspect). Of the group, 270 Mbps and 360 Mbps are the most common data rates.

SMPTE 292M - Defines the HD-SDI high definition serial digital interface. SMPTE 292M has data rate of 1.485 Gbps for 4:2:2 component digital in 16:9 widescreen video aspect. Full bandwidth HD-SDI can be transmitted 300 feet (100 m) on standard RG6 coaxial cable, and more than 60 miles (100 km) using fiber optic technology. SMTPTE 292M is considered a single link HD-SDI signal, in that only one coaxial cable is required to transmit the data.

SMPTE 310 - A broadcast standard for transmitting one or more DTV – digital television channels, and ancillary content, as part of a single data stream.

SMPTE 372M - Defines a full bandwidth, 4:4:4 RGB color space and bandwidth up to 2.97 Gbps, which is sufficient for 1080/60p and 1080/24Psf video streams. SMPTE 372M is most commonly associated with dual-link HD-SDI, wherein two coaxial cables are used to carry alternate pixels, thus doubling the data rate and available resolution. The “Super2k” format in digital cinema, 2048x1080, progressive scan, 4:4:4 RGB color space, is the highest data rate possible with one dual-link HD-SDI connection.

SMPTE 424M - Defines a full bandwidth, 4:4:4 RGB color space and bandwidth up to 2.97 Gbps on a single coaxial cable. SMPTE 424M is colloquially known as 3G-SDI, a term used to describe 2.970 Gigabits per second digital video over a single-link coaxial cable. 3G-SDI is capable of supporting HDTV 1080p video at 50 or 60 frames per second. Most 3G-SDI terminal equipment, such as Extron 3G-SDI matrix switchers, simple switchers, distribution amplifiers, cable equalizers, and fiber optic extenders, is capable of supporting standard SDI data rates from 270 Mbps to 2.970 Gbps.

SMPTE pattern - The video test pattern consisting of color, black, and white bands used as a standard for setting up video equipment.

SMPTE/DCI P3 - A color space defined within the Digital Cinema Initiatives - DCI specification for digital cinema systems. SMPTE/DCI P3 offers a color gamut wider than the ITU-R Recommendation BT.709 or sRGB color spaces, but less than ITU-R Recommendation BT.2020.

SMTP - Simple Mail Transfer Protocol. Internet standard for e-mail exchange across systems/networks on the Internet.

SNMP - Simple Network Management Protocol. Allows for management of network devices with administration software.

Snow - Visual noise in a video picture giving the appearance of white flecks of snow.

Software - The programs used to instruct a processor and its peripheral equipment to perform prescribed operations.

Software Decoder - A software decoder provides a means to decode audio/video streams in software without requiring use of a dedicated hardware appliance. Software decoders are typically used on a PCs using a browser page, media player or special purpose application.

SOG - Sync On Green. The combined horizontal and vertical sync signals are integrated with the green video signal.

SONET - Synchronous Optical Networking. A standardized multiplexing protocol that transfers multiple digital bit streams over optical fiber using lasers or light-emitting diodes (LEDs).

Sound level meter - An instrument designed to measure sound pressure level.

Source - The optical source in a fiber optic system, usually an LED or laser diode.

Spanning Tree - IEEE 802.1d. is a protocol that allows networks to prevent loops, or multiple paths from developing between a source and a destination. Network routers communicate with each other using spanning tree protocol to prevent traffic from reaching unnecessary destinations. Spanning tree and other routing protocols prevent multicast video traffic from flooding networks with unnecessary, disruptive traffic.

Spatial Resolution - A measurement of the resolution in a single frame of video. The horizontal resolution multiplied by the vertical resolution.

Speaker (conical) coverage - Ceiling speakers, much like a spot light, generally project audio in a conical coverage pattern. As with any device featuring a conical coverage pattern, the higher it’s mounted, the larger the circle of coverage. As the area of coverage increases, audio amplification wattage must also increase to maintain the same sound pressure level per unit of area of coverage.

Speaker polarity - Loudspeakers of all types have a positive and a negative polarity. A speaker cone that moves forward (out) when a positive voltage is applied is said to have “positive polarity”; conversely, a speaker cone that moves backward (in) when a negative voltage is applied is said to have “negative polarity.” Speakers must be wired in such a way to ensure that they are “in phase”, that is, all speaker cones are moving in the same direction, in or out, at the same time. Audio test generators, such as the Extron VTG 300 and VTG 400, include a test tone (typically a “click” or “pop”) that’s used to check speaker polarity

Spectrum analyzer - An device used to measure and analyze the frequency spectrum of an input signal, usually amplitude (vertical) vs. frequency (horizontal).

Speed of light - 2.998 x 10e8 meters per second.

Splice - A permanent connection between the ends of two optical fibers by mechanically joining them together, or heating to fuse them together.

Splice closure - A housing designed to protect splices in a optical fiber from damage, sealing them from the external environment.

Splice organizer - A device that facilitates the splicing of optical fibers, as well as their permanent storage.

Splice panel - A rack or wall-mounted panel that allows fiber optic cables to be organized and spliced. The panel holds splice trays, cable routing, and slack storage.

Splice protector - In fiber optics, a device used to provide protection and mechanical strength to a fusion splice, so that it can be handled and organized into a splice tray or other storage.

Splice tray - A container that is used to secure, organize, and protect individual spliced optical fibers.

Split screen - A video effect where portions of images from two sources divide the screen.

sRGB - A color space widely used in computers, monitors, and the Internet, as well as consumer digital cameras, printers, and scanners. sRGB incorporates the same color space primaries as defined in ITU-R Recommendation BT.709, the international standard for high-definition video.

SSH - Secure Shell. This protocol allows devices to communicate securely with each other, such as logging into another device over a network, executing commands on a remote device, and/or transferring files from one device to another. It provides strong authentication and secure communications over insecure channels.

SSL - Secure Socket Layer. A protocol developed for transmitting private documents via the Internet. SSL uses a cryptographic system that uses two keys to encrypt data - a public key known to everyone and a private or secret key known only to the recipient of the message.

Stapler cleaver - A fiber optic cleaver that is shaped similar to a stapler.

Static IP - An IP address that has been specifically (instead of dynamically see “DHCP”) assigned to a device or system in a network configuration. This type of address requires manual configuration of the actual network device or system and can only be changed manually or by enabling DHCP. Also see "DHCP."

Static mesh - A basic de-interlacing process used in scalers for video content that contains no movement. This type of processing results in a sharp image with crisp details but will cause images to tear when motion occurs.

Step index fiber - A fiber in which the refractive index is uniform throughout the core. On the other hand, for a graded index fiber, the refractive index of the core varies radially between the fiber axis and the cladding.

Stereo - A process of using separate audio signals on separate channels for the left and right audio, thereby giving depth, or dimension to the sound.

Straight Tip – ST - A popular legacy fiber optic connector with a twist lock design similar to a BNC. The ST connector has a 2.5 mm ferrule.

Stripper - A tool used to remove the jacket that surrounds a cable or an individual wire within the cable. In fiber optics, a stripper is used to remove the buffer coating from an optical fiber.

Sub-frame compression - Compression which is not carried out on an entire frame of video, but only a part of a video frame.

Subnet Mask - Number of bits of the network address used to separate the network information from the host information in a Class A, Class B, or Class C IP address, allowing the creation of subnetworks. In binary notation, a series of 1s followed by a series of contiguous 0s. The 1s represent the network number; the 0s represent the host number. Use of masks can divide networks into subnetworks by extending the network portion of the address into the host portion. Subnetting increases the number of subnetworks and reduces the number of hosts.

Subscriber Connector – SC - A popular fiber optic connector that features a snap (push-pull) coupling type. Being replaced by the LC in most applications.

Subtractive color process - Process used in color printing. Mixing cyan, magenta, yellow, and black (CMYK) produces millions of desired colors. Examples: 0% of C, M, Y and K = white (no ink); 100% of C and M = red; 100% C, M, and Y = process black. Also see "Additive color process."

Subwoofer - A loudspeaker designed to reproduce only the very low end of the audio frequency range, typically one or two octaves between 20 Hz and 80 to 100 Hz.

Summing amplifier - A device which combines the left and right channel audio signals into a single mono channel. It is useful in multi-speaker mono paging systems, or in large stadium and church environments.

Super Physical Contact – SPC - In fiber optics, a specific endface polish for a connector to achieve typically a -50 dB return loss in singlemode applications. SPC polished connectors can be used with PC or UPC polished connectors but are not compatible with APC polished connectors. Intermixing APC polished connectors with UPC/SPC/PC polished connectors can damage the fiber optic cable or equipment. Multimode applications always use PC, SPC, or UPC polished connectors.

Superimposition - Placing one image over another so that both may be seen at the same time. The effect can be achieved in many ways: by more than one exposure on a single piece of film, by multiple printing, or by registered projection. Abbreviated “super.”

SVGA - Super VGA. A screen resolution of 800x600 pixels and above.

S-VHS - Super-Video Home System. A high band video recording process for VHS that increases the picture quality and resolution capability. Also see "S-video."

S-video - A composite video signal separated into the luma (“Y” is for luma, or black and white information; brightness) and the chroma (“C” is an abbreviation for chroma, or color information).

Sweep - In audio, a sequence of puretone frequencies used to generate a frequency response curve.

Switch - A device that cross-connects network devices. Today, switches are broadly deployed on modern industrial and consumer networks. Switching is a layer 2 function. Ethernet frames are delivered between MAC address connected to network switches.

Switched Fabric - A network topology where network nodes connect with each other via one or more network switches (particularly via crossbar switches, hence the name). The term is in contrast to a broadcast medium, such as early forms of Ethernet.

Switcher - (1) A device that allows a selection between more than one source, such as video cameras, VCRs, etc. In audio/video, switchers are a means of connecting an input source to an output device or a system. Also see “Matrix switcher.” (2) A term often used to describe a special effects generator; a unit that allows the operator to switch between video camera signals. Switchers are often used in industrial or security applications to switch between video cameras that view certain areas for display on a monitor, or system of display devices. These kinds of switchers do not have sync generators. Also see "Matrix switcher."

SXGA - Super Extended Graphics Array. A graphics standard with a resolution of 1280x1024 (1,310,720 pixels), with an aspect ratio of 5:4. This exceeds XGA (1024 x 768, at 786,432 pixels).

SXGA+ - Introduced in 2004, a graphics standard with a resolution of 1400x1050 (1,470,000 pixels) with an aspect ratio of 4:3.

SxRD Silicon xTal Reflective Display - A reflective liquid crystal display technology from Sony that’s capable of very high resolutions and a very high contrast ratio. SxRD equipped projectors are capable of resolutions up to 4096 x 2160 pixels, or four times the resolution of HDTV (1920x1080).

Symmetrical processing - Two processes are symmetric if the input process is of equal magnitude and complexity to the output process. The encoding and decoding processes in the PURE3 codec are symmetric.

Sync - Synchronization. In video, sync is a means of controlling the timing of an event with respect to other events. This is accomplished with timing pulses to insure that each step in a process occurs at the correct time. For example, horizontal sync determines exactly when to begin each horizontal scan line. Vertical sync determines when the image is to be refreshed to start a new field or frame. There are many other types of sync in a video system. (Also known as “sync signal” or “sync pulse.”)

Sync generator - A circuit that produces sync impulses used to control the time when certain events happen electronically. Also known as a “synchronizing pulse generator.”

Sync polarity - (1) A circuit can be designed to operate on the positive-going or negative-going part of the sync pulse. Some equipment has a sync polarity option switch to allow selecting which edge (plus or minus) to trigger on. (2) This refers to the duty cycle of the sync signal. A positive polarity sync signal is low most of the time, and high for a short time. Negative polarity sync is high most of the time and low for a short time.

Sync termination adapter - See "ASTA."

Synchronisation - Timekeeping which requires the coordination of events to operate a system in unison. Synchronisation in video systems can refer to a number of items. Lip-sync is the synchronisation of audio and video. Genlock refers to alignment of vertical sync in video signals. Framesync or framelock refers to the alignment of video frames in systems with multiple video sources.

Synthetic Images - Synthetic images are produced in artificial processes, for example in video processing or computing systems.

System switcher - An A/V switching device that also communicates with other components in a system including room lights and motorized devices. For instance, in addition to controlling a projector, a system switcher can turn lights on and off and raise and lower a motorized projector screen.


t.120 - CCITT standard for digital computer data interchange videoconferencing.

Tap - A fiber optic coupler with two outputs, the second of which, part of the incoming light is tapped off into another fiber.

TCP - Transmission Control Protocol. A method (protocol) used along with the Internet Protocol to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called a packet) that a message is divided into for efficient routing through the Internet.

TCP (Transmission Control Protocol) - A connection-oriented protocol designed to provide a reliable end-to-end data delivery over an unreliable internetwork.

TCP/IP - Transmission Control Protocol/Internet Protocol. The communication protocol of the Internet. Computers and devices with direct access to the Internet are provided with a copy of the TCP/IP program to allow them to send and receive information in an understandable form.

TCP/IP Model - A set of communications protocols used for the Internet and other similar networks. It is named from two of the most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP). The eight functions of the OSI model have been combined into only four layers in the TCP/IP model.

Tee coupler - A T-shaped fiber optic coupler with one input and two outputs.

Telecommunications - An electronic method of transmitting information from one location to another over a telephone network.

Telecommunications closet - An enclosed, secure space for housing telecommunications equipment, cable terminations, and cross connects.

Teleconferencing - A meeting between people at two or more locations who can communicate by audio and/or visual devices often via telephone and/or closed-circuit television. Also see "Videoconferencing."

Telepresence - A set of technologies which allow a person to feel as if they were present, to give the appearance that they were present, or to have an effect, at a location other than their true location. Telepresence solutions include the delivery of audio, video, data and computer graphic information over IP networks using video over IP encoders and decoders.

Telnet - A computer network utility available on most PCs that allows the computer system to communicate with one of its remote users or clients. A user who wishes to access a remote system initiates a Telnet session using the address of the remote client. The user may be prompted to provide a user name and password if the client is set up to require them.

Temporal - Relating to the sequence of time or to a particular time.

Temporal Resolution - A measurement of elements occurring in time. Example: the temporal resolution of video may be 50 or 60 frames per second.

Terminal - A device typically having a keyboard and display that is capable of sending text to and receiving text from another device, a network, etc.

Termination - 1. A load or impedance at the end of a cable or signal line used to match the impedance of the equipment that generated the signal. The impedance absorbs signal energy to prevent signal reflections from going back toward the source. For video signals, termination impedance is typically 75 ohms; for sync signals, it is usually 510 ohms. 2. A connector at the end of a cable.

Termination Tools - Tools used in the preparation and installation of connectors on cables or optical fibers.

Terminator - A device that provides termination for a signal line or several signal lines at the end of a cable. Usually a close-tolerance resistor for each signal, a terminator is often mounted in its own enclosed connector, making it easy to install. In fiber optics, an optical plug used to fully terminate the optical path so no light is reflected back toward the source.

TFT - Thin Film Transistor LCD panel. A type of LCD flat panel display screen in which each pixel is controlled by one to four transistors. The TFT technology provides the best resolution of all the flat panel techniques, but it is also the most expensive. TFT screens are sometimes called active matrix LCDs.

THD - Total Harmonic Distortion. The amount of internally generated noise in a receiver that varies from the ideal sound wave. Since the perfect audio wave is physically impossible, the variation from the ideal wave is the percentage referred to as THD.

THD+N - Total Harmonic Distortion plus Noise. THD+n is a specification that includes both harmonic distortion of the sine wave and non-harmonic noise. THD+N tells the user what amount of hum, noise, and interference has been added to the audio signal by the equipment through which it is passing.

Thin Client - A computer or a computer program which depends heavily on some other computer (its server) to fulfil its traditional computational roles.

Third octave - A term that refers to frequencies spaced three octaves apart. For example, the third-octave above 1 kHz is 8 kHz. Third-octave filters, typically in a bank between 20 Hz and 20 kHz, are useful because they have a good correlation to the subjective response of the human ear. Filtering broad spectrum pink noise through a third-octave filter is often used to characterize acoustical systems, such as loudspeakers, or for the measurement of absorption or damping of acoustical materials.

THX - Originally part of Lucasfilm, Ltd., THX embodies a series of certification programs for equipment, software, production environments, and presentation venues with the objective of delivering optimum sound and video.

Tight buffered cable - A fiber optic cable for indoor use in which the buffer coating tightly surrounds the cladding for extra protection and provides color-coded identification.

Time base corrector - Video tape recorder (VTR) playback circuitry used to smooth out the wavering edges of a video image.

Time base error - Slight errors in the line-to-line position of video information that occur between recording and playback. At the time of playback, these appear as serrations, tending to make the edges of the image waver.

Time base generator - A sync generator which puts a clock signal on the videotape to refer to for precise horizontal lock-up of an image.

Time code - A digital or binary code used to label each frame of a video signal. This is very useful for editing the video since the time code is in the form of hours, minutes, seconds, and frames.

Time division multiplexing – TDM - A digital transmission scheme where the channel is divided into two or more time slots or subchannels, such that the subchannels are taking turns in the bit stream. Multiple digital signals are multiplexed into a serial digital stream. The serial digital stream is transmitted to the receiver where it is de-multiplexed into the individual digital signals

Time domain - A means of representing a signal on a graph of amplitude (usually on the vertical axis) versus time (usually on the horizontal axis). An oscilloscope produces a time domain representation of a signal. Also see "Frequency domain."

Tint - A relative measure of the amount of white in a given color. Also see "Hue."

TLS - Transport Layer Security. The TLS protocol provides a secure communications channel over the Internet. It allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery.

TMDS - Transition Minimized Differential Signaling. An all-digital video transmission standard developed by Silicon Image, Inc. TMDS is the core technology used in DVI - Digital Visual Interface and HDMI - High Definition Multi-media Interface.

Toggle - To switch between alternate states. For example, between on and off, or caps and lower case.

Toggle switch - A switch having two positions or two states. When an activating force is applied, the state changes.

Toneburst - A group of short duration audio frequencies, from 20 Hz to 20 kHz, used to evaluate the behavior of a listening environment in response to loudspeakers. Toneburst is used to identify room reflections caused by resonance or standing waves. Also see "Room mode."

TOSLINK - An optical fiber connection standard for digital audio developed by Toshiba. TOSLINK is very commonly used for audio output from Compact Disc and DVD players, as well as some game consoles. A generic name, “EIAJ optical,” is sometimes used to describe this standard.

Total internal reflection - The total reflection of light as it reaches a boundary between two optical media at an angle of incidence greater than the critical angle.

Touch panel - A control panel with a flat surface (usually with graphic divisions or buttons) that functions as a switch or control. Also called a “touch screen.”

Touchpanel - A control panel with a flat surface (usually with graphic divisions or buttons) that functions as a switch or control. Also called a "touch screen."

TP - Twisted Pair. Cable that uses small twisted pairs of wires in a common jacket/sheath to transmit and receive network or telephone signals; can be either shielded (STP) or unshielded (UTP). The Extron product family includes twisted pair transmitters, twisted pair receivers, and twisted pair cabling.

Transceiver - A device that can operate as a transmitter, receiver, or both.

Transcoder - An electronic device designed to convert one signal type to another, and vice-versa. For example, the Extron YCS Transcoder both decodes composite video into S-video, and encodes S-video into composite video.

Transducer - In audio, a device to convert sound to electrical energy or vice versa. Microphones and loudspeakers are two type of transducers. Microphones convert sound into electrical energy; loudspeakers convert electrical energy back into sound. More Info: Converting SD footage for use in an HD production is an example of upconversion, while converting HD footage to SD is downconversion. Cross conversion converts video from one HD format to another, such as 1080i to 720p.

Transform - A transform is a method applied to convert a data set from one domain to another. The rationale for transforming the data into a new domain is typically to make handling and processing the information easier. One common example is the RGB to YUV color space transformation. Imagery collected from the real-world using sensors in done so in an RGB color space. The RGB information is then transformed to a component YUV domain allowing independent processing of luminance and color information.

Transformation - A change or alteration. In the context of still image compression, a picture frame is input as a fixed resolution of rows and columns of pixels and a transformation into a frequency domain applying the Discrete-Cosine Transform.

Transformer taps - A transformer is a simple device that “transforms” electricity from one voltage to another. Transformers are added to conventional, 8 ohm loudspeakers to adapt them for use in constant voltage, multi-speaker distributed audio systems. The transformers are “tapped”, that is, designed with several different output points, to allow for different output wattages from the 70 V or 100 V constant voltage input. Taps are typically spaced at 2x increments, for example, 2 watts, 4 watts, 8 watts, 16 watts, etc.

Transistor - An electronic component that acts as a valve, or switch, allowing one signal (voltage or current) to control another.

Transmit – Tx - In fiber optics, the light source, such as an LED or laser.

Transmitter - A device that converts from one signal type to another for transmission.

Transport Stream - A defined package for delivering data. Transport Streams are multiplexes of audio, video and other content which are usually broadcast over-the-air, although they can be streamed over IP networks too.

Trigger - A signal, typically TTL level, that is transmitted in order to synchronize two or more instruments.

Tri-level sync - A sync level scheme developed for HDTV in which the sync line first goes low, then transitions high while going through the reference voltage level, and then drops back down to the reference voltage. The transition of the positive-going sync signal through the reference voltage is the sync trigger.

Triple-Action Switching™ - A process in which the RGB signal is muted during the switching, until the projector has time to sync up to the new image. This way, when a switch is made, viewers don't see the image scrambling that occurs until the projector syncs up. Instead, they see the image go blank and then the new image appears already synced up. This provides a professional appearance for presentations.

TTL - 1) In electronics, Transistor-to-Transistor Logic. A digital signal, usually 4-5 volts peak-to-peak with a distance limitation is 6-10 feet (1.8-3.0 meters). Signal splitting is acceptable. TTL signals are either on or off, and are characteristic of low resolution computers (CGA/EGA). 2) In network video streaming, Time to live. Multicast streaming traffic is typically programmed with a TTL value indicating the number of router hops that are permissible for the packet.

Tunable Laser - A laser in which its central wavelength can be varied or optimized as desired for a particular application.

TVL - TV line. A resolution specifying the amount of black and white alternating lines that can be displayed in horizontal or vertical directions. It can be applied to both continuous media video devices (B/W CRT, three-gun CRT projector) and fixed pixel video devices (LCD, DLP, plasma). It’s generally different from the pixel counts of a fixed pixel video device. Also see "Kell factor."

Tweak - To adjust or fine-tune.

Tweeker - A small screwdriver for making sensitive adjustments to audio/visual and other electronic equipment. An Extron specialty.

Tweeter - A loudspeaker designed to reproduce high-pitched or treble sounds in the range of 4Hz to 20 kHz.


UDP (User Datagram Protocol) - A connectionless protocol providing “best effort” delivery of packets across networks. UDP is frequently used in real-time streaming applications were best effort delivery is acceptable and the network devices and applications manage data flow control and errors.

UHD - Ultra High Definition is the formal, industry recognized, name of the standard that includes better and more accurate color (HDR) and better motion rendering with 4K resolution.

UHF - Ultra High Frequency. A television broadcast frequency range between 300 and 3000 MHz on channels 14 through 83. Also the name for a type of connector used for video cables.

UL® - Underwriters Laboratories. When marked by the UL symbol, a product has been tested and evaluated according to nationally recognized safety standards with regard to fire, electric shock, and related safety hazards. There is also a UL for Canada, sometimes called CUL, and a UL recognized component with its own symbol, resembling a backward "UR."

Ultra Physical Contact – UPC - In fiber optics, a specific endface polish for a connector to achieve typically a -60 dB return loss in singlemode applications. UPC has become the most common polish for fiber optic connectors in digital applications. UPC polished connectors can be used with PC or SPC polished connectors but are not compatible with APC polished connectors. Intermixing APC polished connectors with UPC/SPC/PC polished connectors can damage the fiber optic cable or equipment. Multimode applications always use PC, SPC, or UPC polished connectors.

Unbalanced audio - An audio output where one of the two output terminals is at ground potential.

Underfilled Launch Condition – ULC - In fiber optics, a condition where the incoming light only fills a small percentage of the fiber core.

Underscan - A decreasing of the raster size (H and V) so that all four edges of the picture are visible on the screen. Underscanning allows viewing of skew and tracking that would not be visible in normal (overscanned) mode. It is also helpful when aligning test charts to be certain they touch all four corners of the raster. Likewise, when checking the alignment of multiplexer images from a film chain, underscan allows proper framing of the projected image going into the video camera.

Unicast - The sending of messages to a single network destination host on a packet switching network. Sending a separate copy of the media stream from the server to each recipient.

UPS - Uninterruptible Power Supply. A power supply that continues to provide voltage for a limited time after the main power is off (fails).

URL - Uniform Resource Locator. This is the address that lets a resource on the internet be identified, located, and accessed

USB - Universal Serial Bus. USB was developed by seven PC and telecom industry leaders (Compaq, DEC, IBM, Intel, Microsoft, NEC, and Northern Telecom). The goal was easy plug-and-play expansion outside the box, requiring no additional circuit cards. Up to 127 external computer devices may be added through a USB hub, which may be conveniently located in a keyboard or monitor. USB devices can be attached or detached without removing computer power. The number of devices being designed for USB continues to grow, from keyboards, mice, and printers to scanners, digital cameras, and ZIP drives.

USB 1.1 - Universal Serial Bus 1.1. An external bus standard that supports data transfer rates of 12Mbps and 1.5Mpbs. A single USB port can connect up to 127 peripheral devices. Also see "USB 2.0."

USB 2.0 - Universal Serial Bus 2.0. An external bus standard that supports data transfer rates up to 480Mbps, 12Mpbs, and 1.5Mpbs. USB 2.0 is an extension of USB 1.1 and is backward compatible with USB 1.1, using the same cables and connectors. Also see "USB 1.1."

UV - Ultraviolet. Light/heat rays that have a shorter wavelength (and higher frequency) than those in the visible spectrum. UV rays are ordinarily filtered or blocked to prevent eye damage and dye fading.

UXGA - Ultra Extended Graphic Array. 1600 x 1200. A UXGA display has 1600 horizontal pixels and 1200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector.


V - (1) Vertical (as in RGBHV), or the vertical sync connector on a panel. This is used when the sync is separated into horizontal and vertical components. (2) In electrical specifications, “V” is the abbreviation for volts.

VAR - Value Added Reseller. A party who purchases a product, adds something to it, such as hardware or software, and then sells it as a package.

Variable Bit Rate (VBR) - Varies the amount of output data per time segment. VBR allows a higher bit rate or storage space to be allocated to more complex segments of video and a lower bit rate to be allocated to less complex segments.

Variable level control - This is a variable voltage level control similar to a contrast control on a data monitor. The level control increases or decreases the levels of red, green, and blue simultaneously, thus not affecting the adjusted grayscale of the monitor or projector.

Vault - A storage product that houses fiber optic cable slack and splice trays.

VCA - Voltage Control Amplifier. An amplifier whose output is controlled by varying its voltage rather than by direct resistance (as with a potentiometer). VCA’s are typically used in audio mixers; instead of the signal being directly manipulated by the fader (and being subject to inconsistencies in the fader itself), the fader controls a voltage that corresponds to a certain sound level.

VCO - Voltage Control Oscillator. Voltage-controlled oscillators are commonly found in wireless systems, frequency synthesizers, and other devices that must be able to tune across a band of frequencies.

VCR - Generally defined as Video Cassette Recorder. In Europe, however, VCR is a trademark for a particular video format developed by Philips.

VCSEL - Vertical Cavity Surface Emission Laser. A high speed, low cost laser diode that emits perpendicular to the surface of the chip, rather than from an edge.

Vectorscope - A special oscilloscope used in video systems to measure chroma.

VersaTools® - Extron product family of compact, affordable, and versatile solutions for common A/V system applications.

Vertical blanking - Turning off the electron beam in a CRT during the time the beam returns from the bottom of the screen to the top after scanning each field of a picture. If vertical blanking does not occur, a diagonal retrace line will display from the lower right to the upper left of the screen. Also see "Retrace."

Vertical Blanking Interval - VBI -

Vertical centering control - Adjusting the vertical centering control one way shifts the displayed image toward the bottom of the screen and the other way shifts the displayed image to the top of the screen. Also called “vertical shift,” or “vertical position.”

Vertical double images - A video problem in which the display is split across the middle with two identical (squeezed) images on the top and bottom of the screen.

Vertical filtering - This is a feature in some Extron scan converters that controls the number of lines to process, and the way they are processed. This affects the sharpness vs. flicker of the scan-converted picture.

Vertical Frequency - See "Refresh rate."

Vertical interval - The period of time between the end of one video field and the beginning of the next. During this time, the electron beam in a camera, monitor, or projector is turned off (blanked) while it returns from the bottom of the screen to the top. The portion of the video signal that represents this time period may also be called the vertical interval.

Vertical resolution - Also known as “vertical definition.” The number of distinct horizontal lines, alternately black and white, that can be seen in a TV image. Vertical resolution is fixed by the number of horizontal lines used in scanning.

Vertical temporal - A scaling process for video content that contains movement. This type of scaling process employs an averaging technique to merge the odd and even fields of video into a single frame. This type of processing treats the entire picture as if in motion and results in less motion artifacts. Disadvantages include blurring and loss of vertical resolution.

VESA - Video Electronics Standards Association. A nonprofit member organization dedicated to facilitating and promoting personal computer graphics through improved standards for the benefit of the end-user.

VGA - Video Graphics Array. A widely used analog interface between a computer and monitor that uses a 15-pin plug and socket. The original VGA resolution was 640x480 pixels.

VHF - Very High Frequency. Television broadcast range between 30 and 300 MHz, on channels 2 through 13. The FM radio band is between channels 6 and 7 (88 to 108 MHz).

VHS - Video Home System. The half-inch videocassette format originated and developed by JVC and adopted by a number of different manufacturers.

Video - A format for transmitting and storing moving pictures. Video is transmitted and stored in various analog and digital physical formats.

Video amplifier - A low-pass amplifier with a bandwidth of 2 to 10 MHz, used to strengthen the video signal for TV transmission and reception.

Video connector - The connector on the video card or computer’s graphics output that is connected to the video input on the local monitor.

Video projector - A device that projects a video image onto a presentation surface.

Video standards - See "SECAM."

Videoconferencing - Conducting a live conference between two or more locations using video cameras, microphones, and video monitors. The participants can be seen as well as heard. Referred to as a virtual conference room. Also see "Teleconferencing."

Video-follow-audio - In videoconferencing, when the video source switches automatically to show the person speaking, regardless of the location.

Virtual map - Used with the Extron virtualized matrix switchers (Matrix 3200/6400/12800 Series), a virtual map is made of tables stored in memory that relate physical connectors (on the back panel) to logical connections (as seen by the user). In printed form, this can show physical input/output connector numbers as they relate to virtual input/output numbers.

Virtual memory - The process of increasing the apparent size of a computer’s random-access memory (RAM) by using a section of the hard disk storage as an extension of RAM.

Virtual switching - A means of making real, physical input or output ports appear to have different numbers. For example, the Extron Matrix 6400 Switcher can be programmed to switch a set (group) of connectors as one. Also see "Virtual map."

Visible Light - The region of the electromagnetic spectrum that is visible to the human eye, from 380 to 770 nm.

Visually Lossless Compression - Allows the reproduced image to appear to human vision to be identical to the original image.

VITC - Vertical Interval Time Code. Timecode information that is stored on specific scan lines during the vertical blanking interval.

VLAN - Virtual LAN. A group of devices on a network with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN is a Layer 3 network function. A group of network devices can be grouped together into a functionally separate logical network. VLAN and their network traffic will be segmented from other devices that may be connected to the same physical system.

VLB - Video Loopback. A feature in some switchers that allows a video signal to exit to another device, such as a decoder or scaler, and the output of that device is then used as another input to the same switcher. This allows any switcher input to use the decoder or scaler, saving the cost of buying separate units.

VOD - Video on Demand. Unicast streaming video offered by service providers that enables the reception of an isolated video session per user with rewind, pause, and similar VCR-like capabilities.

Volt - The electrical potential difference or electromotive force that will cause current of 1 ampere to flow through the resistance of 1 ohm. Symbolized by “V.”

Voltage - The electrical potential difference or electromotive force expressed in volts. Also see "Volt."

VPN - Virtual Private Network. A method of providing a private network connection via a secure communications tunnel over the Internet. VPNs maintain privacy applying tunneling protocol, encryption, and security procedures.

VS - VideoShift™. A technique used to move a video image around on the screen to prevent burn-in, or destruction of the phosphor. For example, burn-in can occur on flight schedule monitors in airport terminals, where the same image stays on the screen for a long period of time.

VTG - Video Test Generator. An Extron device that generates video test patterns at scan rates that simulate the most popular applications.

VU - Volume Unit. A unit that is designed to measure perceived loudness changes in audio. 100 VU is 100 percent of the audio that is supposed to be present. VU is measured on a VU meter.

VU meter - Volume Unit meter. For audio systems or recorders, a VU meter is a device that indicates the relative levels of the audio being recorded or played. It is usually calibrated to show a maximum recording level to avoid tape saturation and distortion


WAN - Wide Area Network. A computer network that covers a broad area such as a link across a metropolitan, regional, or national boundary.

Watt - A unit of electrical power used to indicate the rate of energy produced or consumed by an electrical device. One watt is one joule of energy per second. Also see "Power (electrical)."

Waveform - A display of a signal (on an oscilloscope) that shows the magnitude of current or voltage signals with respect to time. By displaying the waveform of a signal on an oscilloscope, the time between cycles can be measured and its frequency can be calculated.

Waveform monitor - A special oscilloscope used to display and analyze electrical (voltage or current) signals.

Waveguide - An acoustic device built into a loudspeaker enclosure that improves the efficiency of the speaker by confining the movement of a sound wave to travel over a desired path. In brief, a waveguide is a tube-like structure, straight or folded, that couples the motion of the loudspeaker cone to the motion of the air in the tube. This allows a small speaker driver to create clear sound, without distortion, even at the high volume levels required for low frequency reproduction.

Waveguide Dispersion - The distortion of an electromagnetic signal, or in the case of fiber optics, light as it encounters a waveguide and is dispersed into multiple components of different modes or wavelengths.

Wavelength - The distance from one peak to the next between identical points in adjacent waves of electromagnetic signals propagated in space or along a wire. Wavelength is usually specified in meters, centimeters, or millimeters. In the case of infrared, visible light, ultraviolet, and gamma radiation, the wavelength is usually specified in nanometers (10e-9 meter) or Angstroms (10e-10 meter). Wavelength is inversely related to frequency. The higher the frequency of the signal, the shorter the wavelength.

Wavelength Division Multiplexing – WDM - The combination of two or more optical signals at different wavelengths for transmission within a single optical fiber.

Weighting filter - A special type of band-limiting filter used in measuring audio loudness levels that “weights”, or gives more attention to, certain frequency bands. Common weighting filter designs include: A-weighting, a wide bandpass filter, centered at 2.5 kHz, that mimics the way we hear (see “Fletcher-Munson Curve”); and C-weighting, generally “flat” frequency response with -3 dB attenuation at 31.5 Hz and 8 kHz.

WEP - Wired Equivalent Privacy. This security protocol is used for Wi-Fi networks and provides a level of security and privacy comparable to what is usually expected of a wired network.

White - The lightest visible surface created by a reflection of all colored light.

White level - In television, the signal level that corresponds to the maximum picture brightness. The white level is set by the contrast control.

White light - A blend of multiple colors of the visible portion of electromagnetic spectrum, resulting in light that is white in color to the human eye.

White noise - Noise with random amplitude (strength) over a wide frequency range. Used to test speakers for resonance and sensitivity. Low levels of white noise can be used to cover up other random noises, for example, in an open office environment.

Wideband - A relative term indicating a high bandwidth.

Wipe - A visual transition between images during which the edge of one image moves across the screen revealing the next image.

WLAN - Wireless Local Area Network. A form of local area network that uses radio waves to transmit data between nodes rather than through cable. Mobile devices, such as laptop computers and personal digital assistants, have helped spawn the “plugless” connection to WLANs. The IEEE 802.11 standard specifies the technologies for wireless LANs.

Woofer - A loudspeaker designed to reproduce low frequencies.

Workstation - A type of computer used in design or development work, such as engineering and CAD, requiring a moderate amount of computing power and high-resolution graphics.

Wow - A low pitch audio artifact caused by speed fluctuation in the playback device. Also see "Flutter."

WPA - Wi-Fi Protected Access. This security method provides more sophisticated data encryption and improved user authentication than WEP, which is the original Wi-Fi security standard.

WPA2 - Wi-Fi Protected Access 2. Security method for wireless networks that provides stronger data protection and network access control than WPA.

Wrap-around - A video problem that occurs when the left picture information is displayed on the right side of the screen and the right picture information is displayed on the left side of the screen, separated by a vertical bar.

WSXGA - “Wide-SXGA” defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as the number of individual dots that a display uses to create an image. These dots are called pixels. A WSXGA display has 1920 to 1600 horizontal pixels and 1080 to 900 vertical pixels respectively that are used to compose the image delivered by the projector.

WWW - World Wide Web. An international network of subscriber sites where information in the form of text and/or graphics is made available to computer users (Web site visitors).

WXGA - “Wide-XGA” defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as the number of individual dots that a display uses to create an image. These dots are called pixels. A WXGA display has 1366 to 1280 horizontal pixels and 768 to 720 vertical pixels respectively that are used to compose the image delivered by the projector.


XGA - Extended Graphics Array. A screen resolution of 1024x768 pixels.

XGA-2 - eXtended Graphics Array card, 2nd generation. Capable of scanning from 31 to 68 kHz and resolutions up to 1600 x 1200 pixels, this card uses a 15-pin HD VGA-style connector.

XLR connector - XLR connectorA type of audio connector featuring three leads: two for the signal and one for overall system grounding. A secure connector often found on high quality audio and video equipment. Also called a “cannon connect

xvYCC - Extended-gamut YCC color space. xVYCC can be used in the electronics of televisions and other video displays to improve the image quality of high-definition video signals.


Y - Luminance or luma.

Y Cr Cb - Used to describe the color space for interlaced component video. Also see "Y, R-Y, B-Y."

Y Pb Pr - Used to describe the color space for progressive-scan (non-interlaced) component video. Also see "Y, R-Y, B-Y."

Y signal - The luma signal transmitted in standard color video. In a color picture, the Y signal is made up of 0.30 red, 0.59 green, and 0.11 blue. It is compatible with a standard monochrome receiver.

Y to C delay - Relative delay or timing of the luminance channel compared to the chrominance channel in a video system.

Y, R-Y, B-Y - Color difference signal designation. Y corresponds to the luminance signal; R-Y corresponds to the red minus luminance signal, and B-Y corresponds to the blue minus luminance signal. After luminance is subtracted from red and blue, the remainder is considered to be the green portion of the RGB video signal. These signals are derived as follows: Y = 0.3 red + 0.59 green + .11 blue; R-Y = 0.7 red - 0.59 green - 0.11 blue; B-Y = 0.89 blue - 0.59 green - 0.3 red

Y/C - The technical description of S-video. The luminance signal, Y, and the chrominance signal, C, are carried on separate signal/ground pairs. Because the Y channel is carried separately, higher bandwidth is possible and color subcarrier crosstalk is eliminated.

Y/C separator (YCS) - A Y/C separator isolates the luma (Y) and chroma (C) components of a composite video signal. This is the first step necessary in decoding composite video.

YUV - Defines color space in terms of Y – luminance or brightness, and two color-difference components, U - red minus luminance and V - blue minus luminance. YUV is interchangeable with “Y Cb Cr” for digital component video and “Y Pb Pr” for analog component video.


Z - A symbol for impedance.

Zipcord - A cable comprising two jacketed wires or optical fibers that are conjoined together and can be separated.

Zoom - A term used with cameras and video displays related to the ability to change the view anywhere between near and far. Definitions for near and far vary from one device to another.

Zoom lens - A lens with a variable focal length.

The AVNetwork staff are storytellers focused on the professional audiovisual and technology industry. Their mission is to keep readers up-to-date on the latest AV/IT industry and product news, emerging trends, and inspiring installations.