Demystifying Digital Terminology by Margot Douaihy

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HDMI, CEC, EDID...Is the tornado of digital acronyms making you dizzy? This glossary of easy to understand definitions — provided by Crestron, edited by AVT — will help tech managers and your staff demystify digital media. Watch the video glossary of crestron.com/digitalmedia.

CEC

CEC stands for Consumer Electronics Control. It was designed to simplify communications and control of HDMI connected devices. It allows up to 10 AV devices to discover and talk to each other via HDMI. CEC is intended reduce or eliminate the need for multiple remotes and button commands.

CEC is a single wire bus inside standard HDMI cables. It is mandatory for HDMI devices to have CEC. While it is not mandatory to implement it, AV manufacturers have started incorporating CEC into their products.

 Inconsistent support among manufacturers has made it difficult to enforce industry standards for interoperability. If there's no control system, CEC offers simplicity and convenience. But CEC commands are automatic. They are programmed to occur whether you want them to or not. So, if you have a distributed AV system or a control system installed, the CEC data can interfere with the functionality of the system.

CEC technology is more commonly known by brand names such as LG SimpLink, Panasonic EZ Sync, Sony BRAVIA Theatre Sync and Samsung Anynet. Unfortunately, none of these systems are compatible with each other.

DisplayPort

DisplayPort, released in 2008, is the latest generation interface between computers and monitors. The DisplayPort standard was developed to provide a single high-bandwidth digital interface for the laptop and desktop computer markets.

DisplayPort is both an internal firmware, or "chip to chip" technology, and an external transport technology, often referred to as "box to box".

Historically, there have been three different interface technologies used in PCs. VGA and DVI for connectivity to external monitors; and LVDS for connectivity between the internal display driver of a laptop and its embedded LCD screen.

Because it can support both internal and external communication, DisplayPort can replace the other three.

VGA, DVI, and LVDS all have limitations, such as transmission distance, clock speed and bandwidth. DisplayPort resolves most of these issues.

As a packetized protocol, DisplayPort carries its own clock within the data stream. This eliminates skew issues and requires fewer wires. Packetized data uses available bandwidth more efficiently, so DisplayPort can handle higher resolutions and more types of audio, video and data than VGA or DVI.

Similar to HDMI, DisplayPort consolidates signal transmission into a single cable and supports full, uncompressed HD video—1080p and Deep Color—as well as HDCP content protection and multi-channel audio.

On the other hand, DisplayPort does not support CEC device control or Dolby and DTS 8-channel audio. Today, many PC laptops and MacBooks feature only DisplayPort outputs; VGA and DVI ports are disappearing.

Most HD video displays offer only an HDMI input. So, a converter cable (otherwise known as a dongle) is needed to connect a computer to a video display. The DisplayPort chip inside the laptop or computer detects the connected dongle and automatically converts the output signal to HDMI. It is common today to have computers as content sources, both at home and in the office. So, the need to manage PC and Mac-based media is growing.

EDID

EDID stands for Extended Display Identification Data. EDID is information that a display sends to a source, telling the source its native resolutions. The source then analyzes the data and sends the best audio and video formats that the display supports.

HDMI, DVI, VGA, and DisplayPort are able to transmit EDID. Analog signals cannot.

So, for example, when a Blu-ray player is powered on, it reads the EDID from the display. The EDID could report that the display is a Samsung 32-inch LCD with a 1280 x 1024 native resolution; it supports 480p, 720p and 1080i video formats and it's an HDMI device with two-channel audio.

The Blu-ray player compares this information with what it can output and sends 1080i video with stereo audio from the HDMI port.

EDID was designed for single point to point communication. It was not intended for distribution. So, what happens when you want to send that Blu-ray movies to multiple displays? What if the displays have different audio and video specs?

Some HDMI switchers will collect EDID data from all connected displays, and then send the lowest common resolution to the source.

Other devices manage EDID by copying the data from one display and pushing that resolution to all displays. So, if the first output is to a 1080p display, then 1080p goes to all displays—even if they can only support 720p. This will result in a blank screen, or even damage lower resolution displays.

On the other hand, if the first output is only capable of 720p, then that's what gets sent to your full 1080p display, too.

There is no standard for managing EDID. How EDID is managed is important for the performance and functionality of your system.

HDMI

HDMI stands for High-Definition Multimedia Interface. HDMI is a port, a cable and a transmission technology. Originally, HDMI was developed as a means to transmit digital HD audio and video on a single cable from a source, such as a cable box or DVD player, to the display. As a simple point to point solution, HDMI was designed to only go about 50 feet. Today, it is the standard format for handling HD signals, but HDMI presents real challenges as custom installers and customers try to distribute these signals—something that HDMI was never intended to do.

Unlike analog AV, HDMI is bidirectional and the cable includes 19 wires rather than one to five, depending on what type of analog signal you're transmitting. HDMI cables come in pre-fabricated lengths from 6 to 50 feet. Bulk cable is not currently available due to the distance limitations. Also, similar to RCA or S-video, the connectors do not lock in place.

HDMI carries multiple audio and video formats including full, uncompressed HD and multi-channel audio. HDMI can transmit either surround sound audio or two-channel stereo, but not both at the same time. HDMI also supports two-way communication protocols such as HDCP, EDID, and CEC. It is the worldwide standard for HD signal transmission. Along with fiber and DisplayPort, HDMI is the only way to handle true HD. However, distance limitations, cable installation, and two-way data management have frustrated custom installers and consumers, slowing full adoption.

HDCP

HDCP stands for High-bandwidth Digital Content Protection. It is a form of digital rights management developed by Intel. Content protection was mandated by the FCC at the request of the movies studios to prevent piracy. By blocking illegal distribution, HDCP has prevented all signal distribution. This has caused some frustration among consumers who used to watch movies in rooms throughout the house, but now they can't. HDCP handshaking also causes the delay when changing channels on your HD cable box or satellite receiver.


Margot Douaihy (mdouaihy@nbmedia.com) is the editor of AV Technology magazine. She has covered the AV industry since 1999 and has taught at Marywood University in Pennsylvania.

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