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Old 09-25-2016, 10:11 PM
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Quote:
Originally Posted by NewVista View Post
Though I'm no expert on VIR, wouldn't locally regenerated (network sourced for instance) burst have precise phase lock to the original and, by extension, the VIR (regenerated?) bursts.

So I'm guessing from this the networks used VIR with their feeds?
Not sure if I understand your question completely.

The local burst must be reinserted to standard amplitude and clean waveform per FCC rules. Therefore, it at least loses its relation to the chroma amplitude, which may have changed due to analog transmission distortion over the network. In practice, the reinserted phase is also adjustable and therefore can be misadjusted. If there is significant phase distortion of the chroma over the network, the phase of the incoming burst may also vary over its width, making it difficult to know where to set the phase of the re-inserted burst. The VIR reference had a much wider burst of chroma during the active line, which was supposed to fix this by ignoring edge distortions. Unlike NTSC, the PAL burst, by alternating phase sequence from line to line, should average out to the correct phase even when phase distortion is present.

The whole idea of VIR was to insert it at the originating studio and not replace it anywhere along the chain, not even at network central control; but not every program had it inserted.

I would note that VIR, occurring once per field, had a much slower control action than color burst, and could not possibly compensate for fast signal variations like airplane flutter.
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