AJA IO LA, Инструкция по установке и эксплуатации, Страница: 46 / 76

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Many people associate FireWire with DV (Digital Video); unfortunately this has led
some to believe that it only works with compressed video. The AJA Io family of
products do not compress video or audio—they simply uses the impressive
bandwidth of FireWire as a conduit to send A/V data to and from the Power Mac.
Important Features of FireWire and Video as Implemented in Io
Products
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Io products use an uncompressed audio/video protocol.
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SDI is 270 Mb/s; there is filler data in the stream; actual transfer is more like
230 Mb/s. Since FireWire 1394a is 400 Mb/s, there is adequate bandwidth for
uncompressed video data transfer.
Using 8-bit Versus 10-bit Video
While both 8- and 10-bit uncompressed video are capable of providing excellent
quality broadcast video, 10-bit represents a significantly higher quality and is
preferable in many situations.
Because 10-bit video has four times the numerical precision when compared to 8-
bit, it has a signal-to-noise ratio 12 db higher than 8-bit video.
Visually, in 8-bit video compared to 10-bit video, you will notice a substantial
difference. In 8-bit video there will be “contour lines” or “striations” visible,
particularly noticeable in scenes having soft gradients like a ramp or sunset. For
example, if a sky region is mostly the same color but varies by only a few digital
numbers from one side of the picture to another, you may see contour lines where
the signal passes from one digital value to the next higher value.
Since each numerical value in a 10-bit system is only one fourth as large as an 8-bit
system's, these contours become invisible and the sky varies smoothly.
10-bit video is often used when the source and output video (or “master”) is also 10-
bit. Even if the input and/or output video is 8-bit, a 10-bit “project” will still
maintain a higher quality when there is a significant amount of effects rendering
involved.
Industry standard professional mastering formats—Sony Digital Betacam for
Standard Definition and Panasonic D5 for High Definition—are both true 10-bit
formats.
Genlock and Your System
For video stability and proper system operation, it’s always best to genlock all
equipment to house sync. Although genlock is not absolutely required for Io or your
system, better quality and repeatable operation will be experienced by doing so.
Usually, this means using a black burst generator output looped through the system.
On the Io panels, house sync is connected to the “Ref Loop” input on the rear
panel. You can then loop the house sync to other equipment (VTR etc.) via the Ref
Loop connector provided below.