Losing audio synch during rough spots on tape?

[justin81]

Hello,

As the title of the post implies, I'm having some trouble capturing and maintaining audio synch. I have some tapes that are several hours long and have multiple programs on them. Some of these tapes are reused. So, what happens is the recording was stopped, there is a bit of blank tape, then the old recording (which was partially recorded over) begins to reappear. Then, a new recording might begin. I'm losing audio synch during these portions where there was a transition between recorded content, blank tape, previously recorded content, new content. I hope that makes sense.

Here is my workflow

VCRs: JVC SR-V101US, Panasonic AG-1980P
TBC: DataVideo TBC 1000
Capture Card: ATI TV Wonder HD 600
Software: Virtualdub 1.9 (LordSmurf version posted here), Huffyuv64

Incidentally, VirtualDub is not reporting any dropped or inserted frames during these rough patches. The audio is just out of sync after they occur. I've experimented enough to the point where I am extremely confident that it is the rough spots on the tapes as described above that is causing the loss of synch.

Is there anything I can do to avoid this problem?

Thanks in advance,
Justin

[latreche34]

You will need to start a new capture every time you loose signal, even if the TBC can magically fix that you wouldn't want to take risks capturing several hours in one shot.

[lordsmurf]

I'm not convinced of that. The TBC-1000 should not care about the "rough spots", and insert new sync.

Of course, there are always unusual issues. Did you record NTSC over PAL, or vice versa? That would trip up the TBC-1000, which auto-senses formats. I can see that happening.

Reused tapes are never easy to work with.

[latreche34]

I'm just saying I wouldn't want to risk capturing several hours just to find out that I need to recapture again due to a minor audio sync problem, TBC's are not 100% perfect, any unwanted noise or miss tracking event can push them off the rail.

[keaton]

Surprising that a Datavideo TBC is in the chain and you have sync issues. That really should nip things in the bud. Another possibility is to review your Virtualdub settings. Review this post in the Virtualdub Settings Guide http://www.digitalfaq.com/forum/vide...html#post45242 In particular, the Timing, General Options, and Resync mode sections of this post.

It's not necessarily a trivial answer what sync settings to use in Virtualdub. You should definitely keeping your Datavideo TBC in the path and see if a change in Virtualdub settings prevents it from trying to resync when it shouldn't.

[latreche34]

The TBC cannot create a signal from thin air, Basically when there is a weak signal or signal with bad timing it corrects it but when the tape passes through areas where there is no signal at all it starts guessing until it recovers the signal again and re-times it, Every time this happens few milliseconds are off and they add up until you notice it.

Maybe the OP can try to disable vdub frame add/drop and let the frame synchronizer inside the TBC (if equipped) handle that and see if that makes a difference.

[justin81]

Thanks for the advice.

To answer lordsmurf's question, these tapes were NTSC all the way. No PAL capabilities here.

I'm going to post a screenshot of my timing settings. I copied these settings from sanlyn's guide to capturing with VirtualDub. I'm using the ATI TV Wonder HD 600, so I changed two things (beyond the settings recommended by sanlyn)

Correct video timing rate for fewer frame drops/inserts - I turned this off
Automatically disable resync when integrated audio/video capture is detected - I turned this on

Any feedback is appreciated!