Clarify some Analogue to DV questions

[Daffypuck]

Sorry to rehash an old subject, but I just want to clarify a few points after Ive done some reading here on the forum. Ive been doing a lot of VHS to DVD transferring and Im wondering if Ive been getting the best out of my captures. The one thing I had never heard of was the mention of TBC's. WHat exactly is that? Is it something that corrects the audio sync? Ive noticed the longer my captures, the more out of sync my audio gets sometimes. And simply moving the audio track down a little doesnt always apply equaly throughout the video. Also, how do I know if what IM using already has TBC? Heres how I capture my sources:
JVC S-VHS (S-video_>SONY DCR TRV320 (As a pass through via firewire)>PC video card firewire input>Premiere>AVI>edit/burn to BD/DVD

Ive recently read about using virtualdub as my capture software. Is there an advantage to that over Premeire? Am I missing anything?

Thanks for any advice

[jagabo]

There are two basic forms of TBC, line and full frame.

A line TBC corrects horizontal sync. If you look carefully at a VHS cap you'll see that individual scan lines move left and right randomly, from line to line and from frame to frame. This is because the read head doesn't spin at a constant speed, it's always slowing down and speeding up, trying to keep a constant speed. The animated GIF image in this post zooms into a small portion of the frame showing the uncorrected output of a VCR and the same frames after a line TBC:

https://forum.videohelp.com/threads/306272-Computer-video-capture-vs-vcr-to-dvd-combo?p...=1#post1882662

Here are some more images:

https://forum.videohelp.com/threads/319420-Who-uses-a-DVD-recorder-as-a-line-TBC-and-wh...=1#post1983288

A line TBC doesn't help when there is a very corrupt signal or complete loss of signal. This is where a full frame TBC comes in.

A full frame TBC produces stable video output whether or not the input is stable. This helps prevent audio sync problems from dropped or duplicated frames. It's basically a video capture device and video playback device. It captures the input signal to its internal frame buffer, then outputs from that buffer to the analog output with perfect sync. That doesn't mean the picture is never corrupt. If the captured video is messed up so is the output picture. But the horizontal and vertical sync pulses and the frame rate of the output signal are always perfect. Even if you turn off the VCR the full frame TBC will continue putting out a clean signal (with no picture or maybe the last picture it received). It's similar to the way your computer continues putting out a perfect signal to your monitor even if your capture device has lost sync.

If your VHS tapes are in good shape, and your capture device can handle an inaccurate signal, you may not need a full frame TBC. But a line TBC is needed for best quality. Aside from looking bad all that horizontal jitter is a killer of video compression.

[Daffypuck]

"If your VHS tapes are in good shape, and your capture device can handle an inaccurate signal, you may not need a full frame TBC. But a line TBC is needed for best quality. Aside from looking bad all that horizontal jitter is a killer of video compression."

So how do I determine if I can handle an inaccurate signal? Is my setup correct for simple capture to edit? Or should I replace/add something to my workflow?

[Cornucopia]

IMO, for VHS, it's more a matter of how often you DON'T need a TBC (answer: not very much).

Scott