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Digital connection standards

Digital Interfaces

If you use multimedia projectors or monitors, you should be aware that digital interface standards are entering our world and the old analog VGA display cable and RCA video will be fading.

Why do we need a digital interface? Primarily because our state-of-the-art display devices (LCD and DLP) are digital, as are our computers. When these large-screen displays were all analog (as CRT-based projectors and TVs are), it made sense to convert the computer's digital information to an analog RGB signal. But it makes less and less sense today. Eliminating the converters will improve performance. Why put up with the conversion loss your image will suffer going from digital to analog and back to digital again?

There are several digital standards to be aware of.

SDI, Serial Digital Interface, is intended for "broadcast quality" digital video, serving SDTV and HDTV (standard and high-definition digital = 1920 x 1080 resolution.

SDI is a high-speed connection at 270 Mbps and 27 mHz clock speed. It is sometimes referred to as 4:2:2 component video (YcrCb), if you want to throw around jargon and get dangerously close to sounding like you know what you're talking about. SDI is carried on one coax cable with a BNC connector and can run hundreds of feet. There is a HD-SDI version.

D1 is another broadcast format that is less commonly used. It uses a parallel multi-pin connection.

DVI, or Digital Virtual Interface, because it can carry virtually any kind of data (video, audio, graphic, or any computer files.). This is becoming the preferred way to connect the local computer to the very near-by display device. A major draw-back is that it has limited range with a transmission distance of 10 meters. It's modestly fast at 25Mbps (165 mHz clock speed) and uses a multi-pin D connector).

Firewire, or IEEE1394 (pronounced "eye-triple-e 1394"), which is popular because it is very easy to use. As plug-and-play capable, you can "hot-plug" it (plug it in with both devices on) and it well self-address to start working. You can use it for video and computer data as well. It is a capable of peer-to-peer connections, without the use of a host computer, so you can connect any two devices with it. And PC manufacturers are beginning to include it on their systems. It runs at a fast 100, 200 or up to 400Mbps. It is scalable and can daisy chain multiple devices.

The downside of Firewire is that you can only run about 5 meters with it. Today you'll see it used for connecting digital cameras and camcorders. Some digital VCRs use this interface but require a decoder to make the signal viewable. Firewire uses a 6-conductor cable delivering serial data through a 1394 proprietary connector.

USB. Universal Serial Bus, primarily used for peripherals (scanners, printers, phones) is important to a/v users for control applications. It is beginning to push RS-232 into the background. It too works with plug-and-play peripherals. It's not fast at 12Mbps, but an upgraded version 2.0 will soon improve that to 480Mbps. USB is also host-centric, which means it only works with a computer.

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