Automatic search for VHS interference?

[aramkolt]

That PDF explaining some variations on dropout compensation was I think probably from the mid to late 1990s and mostly was looking at professional VCRs because those were probably the options that the studio doing the testing was only considering professional VCRs of the time. It's kind of amazing how poorly they did most did with dropouts despite being $5k+ when new, But I suppose back then dropouts were probably less common with all VHS tapes being relatively newer. It is not generally recommended to get older professional VCRs like that mainly because they are overly complex, are likely to get damaged in shipping, are likely have already seen heavy use, and replacement parts are basically impossible to find.

Professional machines like that also usually won't be able to read anything not recorded at SP speed (including the AG-8700 you mentioned) so they may be potentially unusable for your tapes even if they were in perfect working condition.

As for Snell and Wilcox, much of their equipment do have various noise processing and masking features, as well as some having TBC capabilities. However, I don't think that they'll help with actual line-dropouts much. I haven't personally tried it, but my guess is they could do a pretty decent job at removing excess chroma or grain noise, possibly at the expense of softening the image some. Chroma noise usually shows up as a sort of rainbow effect or a sort of red/green mosaic pattern over certain tapes.

Any sort of noise reduction generally is thought to be better handled in software after the fact if you know what you're doing with tools like Avisynth. If you reduce the noise at the time of capture, you can't go back to the original starting point.

I agree with latreche34 that a frame TBC shouldn't be the top concern to add to a video capture chain unless you are getting dropped frames or vertical image jitter. Horizontal jitter is corrected by internal line TBCs most of the time, or if not then by ES10/15 passthrough. Dropped frames become apparent the further you get into longer captures - they'll present as audio sync issues where the audio usually seems to trail the video. What actually is happening is, there are too few frames and the player is going through video frames relatively more quickly than if all the frames were present.

Certain capture cards just tolerate a higher degree of time base errors better than others before they'll drop a frame. VCRs with built in line TBCs or if using an ES10/15 will usually drastically decrease dropped frames. I have a VM700T that can look at composite signal horizontal jitter and just switching on the line TBC on the VCR reduces horizontal jitter by a factor of 50 or more. So going from 1000ns to like 15ns (nanoseconds are the units I think) if I recall correctly.

If you do use an ES10/15 for passthrough, it's generally recommended that the line TBC in the VCR be turned off because they do a similar thing, On a budget, you might just look into getting a modern JVC S-VHS machine without line TBC and pair it with an ES10/15 and see if you like the results.

I still think your main visual issue is one of low tape tension and/or poor dropout compensation - the problem with predicting how dropout compensation will be on any given VCR is that they seem to vary from model to model and unit to unit sometimes. Not sure why that is. I do plan to test a bunch of VCRs against each other on how they handle dropouts, but haven't gotten to it yet, but I'll post the results when I do.

[djslava]

Quote:

Originally Posted by aramkolt

Certain capture cards just tolerate a higher degree of time base errors better than others before they'll drop a frame. VCRs with built in line TBCs or if using an ES10/15 will usually drastically decrease dropped frames. I have a VM700T that can look at composite signal horizontal jitter and just switching on the line TBC on the VCR reduces horizontal jitter by a factor of 50 or more. So going from 1000ns to like 15ns (nanoseconds are the units I think) if I recall correctly.

If you do use an ES10/15 for passthrough, it's generally recommended that the line TBC in the VCR be turned off because they do a similar thing, On a budget, you might just look into getting a modern JVC S-VHS machine without line TBC and pair it with an ES10/15 and see if you like the results.

I also had experience with dropped frames. Initially, I tried to digitize through a MiniDV camera, using it as some kind of TBC, as well as just technically tidying up the ugly signal into a familiar DV file. And I encountered dropped frames when I used Pinnacle Studio 9 for capture (I note that many studios use it, some already use new versions, but they choose it), and the subsequent desynchronization of the sound, since the counter of dropped frames ran up like a stopwatch. Then I found another program - DScaler and there were no problems with it even after directly connecting the VCR to the capture card. Now I pass the signal through ES15, but here's what I noticed: even if the tape is digitized twice on one device or on different ones, their signal will not ideally match in video and sound. Having made one of the video tracks semi-transparent, I noticed that there are moments when one (two fields) video frame is skipped and the sound starts to lag behind by several milliseconds (but this is visually unnoticeable, so it is not critical), and then synchronization is restored when the scene changes. Moreover, on some tape recorders this effect can be more frequent, on others less frequent, which makes me think that the device may have some other built-in processing (although they do not have TBC on board). For example, sometimes it seems that the tape recorder duplicates the previous frame to hide the next one with dropouts. But when switching "from the first to the third frame" there is a small jump. The problem itself is not very critical for me, but it was interesting to know how such a planned resynchronization works technically and whether it is connected with separate reading of video and sound (different heads)? After all, if the tape is recorded in mono, and the tape recorder allows a small amount of flutter, it turns out that the video heads must resynchronize the video sequence using sync pulses, so that the sound matches the video? And this happens before TBC and the rest of the chain? I would like to verify this information with professionals.

As for the poor tape tension, I also came to this conclusion when I was pulling the video out of vertical shaking by increasing the tension. But considering that I have several tape recorders, and they (even if I digitize the tape on each and compare) can often show dropouts on one of the frames to varying degrees, it turns out that they all have weak (standard) tape tension.

There is another point: sometimes I come across a second copy made from the first one, which already contains dropouts. Would PDF devices also cope with such an image, or does processing dropouts, which are already a video signal, not work?

[aramkolt]

Typically when capturing DV through a MiniDV camera, WinDV is usually the way to go on Windows as it is small and efficient.You really shouldn't get audio sync issues on DV, or at least it audio sync should be quite rare anyway. You might give that a try and see how it goes compared to the others.

As for audio delay through an ES15, it is recommended that you pass both the audio and video signal through the ES15 as it should delay the audio by the correct amount that it adds delay to the video stream as well.

On second generation tapes, baked in line dropouts or image issues won't be seen as dropouts since they are recorded that way. There have been some reports that second generation tapes can have some of the horizontal wobble corrected to some degree through certain devices. Even those won't correct dropouts that were on an original tape capture on second generation tapes though since that dropout is stored as a valid video signal on the second generation tape.

[lordsmurf]

Quote:

Originally Posted by djslava

I also want to ask: if I buy a JVC S-VHS with a TBC on board, will the ES15 be enough afterwards or is it important to have a DataVideo TBC-1000 or Cypress AVT-8710?

JVC VCR has line TBC
ES15 has line TBC.

In a workflow, 1st TBC wins, 2nd does nothing.

So if JVC TBC on, ES15 TBC does nothing. WOrse yet, ES15 is only there to make image/audio worse, as it's not a transparent item. It does have the non-TBC frame sync, but it's not a frame TBC replacement.

You'd only use such a config for anti-tearing, where the JVC TBC is off, ES15 is in workflow.

Having frame TBC matters. Right now, you have none. Yes, it is important. We don't own frame TBCs because we like to spend money on something not needed. That's daft, and yet some people wrongly think this. Is the transmission in a car optional? Sure, you could probably weld it to only drive, never park/neutral/reverse, but will will have issues eventually. That's essentially a frame TBC. It's necessary, even if some people wrongly think otherwise.

Quote:

Originally Posted by aramkolt

.You really shouldn't get audio sync issues on DV, or at least it audio sync should be quite rare anyway. You might give that a try and see how it goes compared to the others. .

This is false. Such statements are based on Canopus marketing from 25 years ago. It's based on the wrong understanding of what "audio lock" is in DV, and that has nothing to do with sync.

There's nothing special about DV devices. Those can, and do, lose sync. The device itself is what matters, as well as the software, and settings for both. Some will not sync properly no matter what you do, some have no issues at the defaults. That's the norm for all capture cards, DV or otherwise.

Quote:

Originally Posted by djslava

After all, if the tape is recorded in mono, and the tape recorder allows a small amount of flutter, it turns out that the video heads must resynchronize the video sequence using sync pulses, so that the sound matches the video? And this happens before TBC and the rest of the chain? I would like to verify this information with professionals.

I don't think the heads resync anything, both are constant velocity output without a RAM buffer. Honestly, I don't remember every task that happens in decks without needing a refresher. I'm a VCR user, not a VCR engineer. Different skill sets.