AG-1980: Vertical jitter with or without AVT-8710 TBC. Ideas?

[Mini-Me]

My VHS captures have a lot of vertical jitter, where the individual fields will occasionally jump around 1-4 lines and screw up the interlacing (deinterlacing just yields bouncy frames, of course). "Bounciness" is the best way to describe the behavior. I've been struggling with the problem for months, but it seems to be getting worse over time.

It would be fine if my AVT-8710 could correct the jumpiness, but it does not. The TBC is great at correcting signal fluctuations (which can otherwise throw off my All-In-Wonder's AGC and cause blowouts), but it's not even putting a dent in the vertical jitter. (I'm working on an Avisynth script for this, and it helps a ton, but it's still imperfect, so I want to look closer to the source of the problem.)

Does anyone know why my AVT-8710 won't correct vertical jitter? Isn't it supposed to, since it has access to all the sync information? I thought that maybe my AG-1980's line/field TBC is screwing up the sync information, but the AVT-8710 fails to correct the jumpiness with or without the VCR's TBC enabled. Although some areas of certain tapes are worse than others, the jitter actually occurs on random fields (different ones every time). In other words, it is in fact a playback problem, and it was not baked into the signal upon recording.

Should my AVT-8710 be correcting this jitter, or is it normal for the problem to persist? Where does the jumpiness come from in the first place? I read somewhere that it comes from vibrations in the VCR, but an expert's opinion would be helpful. (If it comes from vibrations, would it still make sense that some areas of tape are worse than others?) What can be done about it?

[robjv1]

Yeah, this is a common problem, especially with these VCR TBCs. Your AVT-8710 is irrelevant in the discussion for this purpose -- it's not going to do much for vertical jitter. Any references below to the TBC are to the VCRs TBC.

I'm of the opinion that there are two types -- those caused by the JVC/Panasonic TBC themselves when engaged and those 'baked' into the signal which these VCRs (and many others) will display this error. I'm not sure that they occur during recording, but they are certainly a problem at playback.

In most cases, vertical jitter is suppressed when you turn the VCR TBC off. If that doesn't take care of it by itself, think about picking up the Panasonic ES10 DVD recorder to use as a pass-through device, which does a great job at suppressing it with the the VCR TBC off. I have very few tapes where it doesn't eliminate it completely or at least to a point where it is barely perceivable. I believe there are a few other models of the Panasonic that perform the same function. Still, I have some tapes where there is occasional vertical jitter (though not nearly as severely pronounced as when the VCR TBC is on) that is pesky. I'd say the ES10 can eliminate 90% of it though. The only negative is the slight impact on picture quality in terms of posterization, most noticeable in dark scenes. Personally, I use it just on the parts that need it, match the colors, and edit that footage into my video, versus using it for the entire run of the tape.

I've tried to find an automated way to deal with this, since I don't like making recordings with the TBC off just for a few small portions where the 'bounciness' occurs, but I've found nothing that works perfectly. AVISynth is a good place to start -- I've played around with some of the dejitter filters to mixed results, but it does mask the error somewhat.

[themaster1]

What kind of content is it out of curiosity: movie, music video, home made video ?

[Mini-Me]

The ES-10 sounds interesting, but considering it doesn't always fix the problem AND it adulterates the picture...I'm not so sure that's something I want to spend money on. Plus, my bouncing may be a bit different from yours, robjv1: Disabling the VCR's TBC actually seems to make the shakiness worse rather than better. While some sections of tape are far worse than others, the jumps aren't directly baked into the tapes either, considering different fields jump every time I capture a tape.

The videos are home movies (NTSC VHS), by the way.

[sanlyn]

Full-frame TBC's like the AVT usually aren't designed to correct the problem you describe. But without a sample of this video, I doubt many readers know exactly what you mean by "jittter". Offhand it sounds as if the video was recorded that way in the original machine; that is, many tapes recorded on one machine don't play properly on others, especially if record/play alignment of the two machines is vastly different.

[davideck]

I assume that you already tried adjusting the tracking. If you're the adventurous type, then you could try realigning your AG1980 tape path to the problematic tapes. A slight tweak might be all that is required, but make sure that you can retrace your steps.

https://forum.videohelp.com/threads/329942-How-to-adjust-VCR-tracking-for-EP-tapes?p=20...53#post2043753

[Mini-Me]

sanlyn, it's a shame if full-frame TBC's can't correct vertical jitter (interlaced fields randomly bouncing up and down a few lines on playback, differently every time). I was under the impression that was one of their functions. I mean, line TBC's horizontally stabilize based on the signal's sync information. That means they know when each line begins and ends. I figured that full-frame TBC's should similarly understand where each field begins and ends: Considering they utilize similar sync information to correctly time frames, I imagined that fixing the timing of individual fields was kind of a prerequisite. Still, if TBC's can't handle vertical stabilization, that would certainly explain why mine won't.

daviddeck, thank you for that link! I'm having a bit of trouble viewing the book page you linked to, but once I see it, I'll see about learning something new and getting my hands dirty.

[davideck]

TBCs can typically handle vertical stabilization from the timing point of view, but they require valid vertical sync intervals off tape to do so. If the VCR tape path is not properly aligned to the tape (or vice versa), then the vertical sync interval can get corrupted or partially removed.

The entrance guide (left side of scanner) is likely to have the most effect on the vertical sync interval (since it is at the top of the picture), so I would recommend that you try adjusting it first.