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Old 10-26-2007, 09:21 AM
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Ampico-kid Ampico-kid is offline
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Join Date: Mar 2007
Location: Harpers Ferry, WV
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Quote:
Originally Posted by blue_lateral View Post
It depends on what problem you are having. Trash in the blanking interval on VHS will cause white lines, just as it does with DVDs. It also contributes to instability, however..... There is another separate problem with VHS. There are rather severe timebase errors that are the root cause of instability in the picture.

Our older sets were designed to play NTSC spec video, over the air. It was assumed that the transmitter would be extremely stable, because the FCC required it to be. The sync sections in the old sets were designed with a "flywheel effect". If a few sync pulses were lost to interference, the picture would not destabilize. The watcher may not have even noticed.

VHS on the other hand, is not extremely stable, quite the opposite. The video is recorded in diagonal slices across the tape, and while there is nothing inherently wrong with that method, the slices do have to be put back together on playback. In the case of VHS, it doesn't get done very accurately.

When the slices get put back together, the time between the sync pulses does not always come out right. An old set will display exactly what VHS gives it, a picture that waves all over the place.

Modern sets use a different method. They do not have the flywheel effect. If a sync pulse comes, a line or frame starts. This has the effect of putting the beginning of each line more or less where it belongs. The playback is much better. This is not because the set is more stable, but because it is less stable.....

I am using a JVC VCR with a timebase corrector. As far as I know they are the only company that offers this on a consumer grade VCR. I haven't looked lately but usually their TOTL model has it. All of the instability goes away when you hit the TBC button. One thing you might not expect is that the color improves too. The difference is staggering, even on modern sets.

John
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Right on John ! I also have a JVC VCR with TBC (Time Base Correction) and it works fantastic. Without it the VHS picture is unstable, waving and jittering all over the place. With the TBC turned on the picture is rock solid with no fluttering, waving, tearing, or jittering at the top of the picture.

The things we have to go through to watch our vintage TV's !

Bob
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