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How to Buy a Small Switcher - AvNetwork.com

How to Buy a Small Switcher

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Four Tips to Making an Informed Purchase


By P. Julian Hiorns

For the purposes of this article, I’ve assumed that most users are interested principally in SD (serial digital) working, and it is certainly my format of preference. Analog switchers are available, but the range is limited, and the vulnerability of the analog format to noise and high-frequency attenuation make it (in my view) a poor second to the SD format. The SD signal is rugged and can be sent over considerable distances without external assistance.

One of the key features in today's market is portability. Some cameras can fit in your pocket, an edit pair can be carried like a suitcase, and appreciable processing power can be squeezed onto your credit card. With this kind of miniaturization available, it's no surprise that some switchers have also moved from the megalithic to the microscopic. For field operations in particular, this is a blessing. Where once you needed an airport cart for your switcher, now you can find one to fit in the pocket of your all-weather jacket.

Of course, this reduction in size is not without its drawbacks, and there's always the risk of the loss of what might be termed operability. Some small production switchers attempt to compress all the features offered on a 32-channel 3ME presentation model into something the size of a large hardback book. Unfortunately our fingers have not shrunk commensurately to match the size of the buttons on such devices.

Tip Number One: go for big buttons. They're easier to find in low-light situations and (usually) more rugged. It's often fair to say that the smaller the button, the easier it is to break.

Tip Number Two: make sure the switcher is strongly built, especially if you're planning to do a lot of location work with multiple rigs/de-rigs. Generally, the smaller the box, the less respect it gets from baggage handlers, so a small portable switcher needs to have the structural integrity of a nuclear materials flask. A metal frame unit is recommended; though heavier than plastic, it will take a lot more hard knocks without folding up. The weight is an advantage in the field too, since you can load the rear panel with a full complement of broadcast video cables without the switcher falling over backwards.

Moving now to the actual operation: what do you need on a front panel? The most extreme adherents to the KISS principle, would restrict front panel operation to an M/E bank (program and preview source selectors) and a "take" button. This is not as unreasonable as it might sound. In practice, most live mixing tends to consist of straight cuts (try watching almost any current music video) with the occasional slow dissolve for dramatic effect. That being said, it is good to ring the changes once in a while, and you may need to do a split screen from time to time, so in practice simple wipes are handy to have. With the wipes come the border and soft edge features, and these can add a nice touch to a transition, so these probably need to be on the front panel as well.

You'll want to be able to change the rate of the auto transition, so some kind of set control and a simple display is very useful, and a similar feature for fade to black is also an advantage.

Tip Number Three: Look for an uncluttered control interface.

Here's a list of the basic features you'll probably need on the front panel.
• Source (channel) selection/program and preview
• Wipe select
• Border/soft edge/wipe reverse
• Mix/wipe
• Fade to black
• Auto/manual (fader) transition
• Take/cross-cut

The image pictured here is the front panel of our Callisto portable switcher. It uses large (3/4-inch square) buttons for source selectors, and the spacing allows for gloved operation (not as uncommon as you might think). To the right of the T-bar (manual fader) is the cluster of controls for take, fade to black and auto/manual selection.

Needless to say, a switcher is a lot more powerful than this simple list of functions would suggest. This is not just because engineers like to invent things (although we do); it's also that the enormous power of modern DSP (digital signal processing) allows for a significant feature set to be developed. However, we're keeping it simple up front, so a lot of features can be stored behind the scenes in a menu structure. We've adopted this approach on our switchers, and it helps to keep the front panel easy to operate. Here are some features that you might see in the menu.
• Test pattern generator (useful for setting up levels downstream)
• Wipe border color
• Wipe edge softness
• Wipe border width
• Frame/line mode
• 525/625 selection
• Editor control
• GPI assignment

Assuming you're working in SD, an issue to consider is the audio handling. If you're working with embedded audio (the audio is carried as part of the serial digital signal), then the switcher needs to have an on-board audio mixer. However, this is only a practical proposition if all your sources are equipped for embedded audio, which tends not to be the case. Given that the cost of audio embedding is still quite high, many users prefer to keep the audio in the analog domain. This presents another problem. Most SD switchers are able to work in asynchronous mode, where the switcher uses internal frame stores to handle free-running sources. The drawback of this is that the switcher will, of necessity, have to insert a maximum of a one-frame delay in the signal path. In other words, the analog audio will arrive at the signal destination as much as one frame earlier than the video. Whether this is a problem or not depends on the application; in some cases an audio delay must be inserted, which means further expense.

There is a way around the problem of audio delay, and for this you need a switcher that can bypass its internal frame stores and work in line mode. This requires all your sources to have reference inputs, which is not the case on some of the smaller camcorders. In line mode, the usual delay through the switcher is a video line or two, and thus there is no appreciable lag between the audio and the video.

The other consideration is that of operational requirements. It is often the case that the audio mixing will have a different profile from the video mixing. In particular, the audio mix will frequently start before the video transition. This is very difficult to set up in the field, and it is frequently easier to edit the audio in post or via a separate audio mixer at the time of recording. Overall, the conclusion is that the audio and video require separate handling, so…

Tip Number Four: keep the audio separate. It's cheaper and makes the operation simpler.
This is a subject of some substance, and the full list of tips could run to many pages. If there's anything you'd like to ask, feel free to visit AVTechnologyOnline.com or BrickHouseVideo.com and send us an email.


--P. Julian Hiorns, Brick House Video, Owslebury, UK






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