VHS-C : Can TBC correct lost vertical sync on recording start?

[cym]

I have a number of VHS-C tapes that I'm capturing to PC, then transfer to DVD. These were recorded on some 1980's era camcorder. When I play/capture them, often the vertical sync is lost at the beginning of each segment where a recording begins, for just a couple seconds . The picture rolls vertical for a couple seconds, then locks in. It doesn't happen on every recording start.

Setup is as follows:

1) Panasonic AG-1980P SVHS deck for playback
2) SVideo out and R/L audio out into analog inputs on the Sony GV-D200
3) DV output on the Sony GV-D200t into my PC.

My understanding is the AG-1980 has a full field TBC (not full frame), and I have this enabled. The manual doesn't say whether it is full field or frame, but googling around seems to indicate full field. Although GV-D200 has a full frame TBC, it does not apply to the analog inputs.

Why is the vertical sync a problem at the starts of recordings? Is it weaker there and more susceptible to age?

Would a full frame, or more capable TBC correct this?

CYM

[edDV]

VTR's/VCR's always need "pre-roll" to lock to rough V sync first, then rough H sync. Then the TBC locks the A/D clock.

Why the delay? All the servo controlled motors need to spin up then stabilize before the input side digital clock does the same thing.

[cym]

edDV,

Thanks for the reply. But this doesn't happen between every new recording segment. One of the most annoying examples is in a musuem where they shot 5 seconds of one thing - stop, then 5 seconds of another thing - stop, etc. But the vertical sync is lost only sometimes between these changes. The VTR I'm playing back is continously playing so it isn't really pre-rolling each time. But, your comment about pre-roll leads me to think that in some cases there's a gap in the sync on the recorded tape, and so the VTR must resync, but in others the sync was continous and sync is not lost, so no vertical roll between those scenes.

Is that what's happening? Nothing I can do with a TBC on the video out?

CYM

[edDV]

My guess is the original VHS-C camcorder was started from a stop state for the unstable clips (e.g. scanner had to accelerate from a stop) vs. from a record pause state where the head is spinning at full speed. The scanner spins much faster than the tape reels.

If this was the case, all you can do is edit out those unstable frames.

[jagabo]

Another problem comes from the erase head on consumer VHS recorders. It is placed ahead of the drum in the tape path. That means there is a few seconds of unerased tape at the beginning of each recording. If something was already recorded on the tape (ie it was a used tape or the tape was rewound before starting the new segment) the new video won't completely overwrite the old video. So you get something like a "double exposure" that makes it hard for the player to sync. This lasts for a few seconds and you can often see remnants of the old video until clean erased tape reaches the drum.