Strange VHS audio sync drift vs. the other digital audio track

[vlp_007]

Dears,

i am have digitalized VHS movie audio into WAV format. As expected, VCR is analog and process of digitalizing is as is. This audio is for me unique VHS movie dubbing which i wanted to add as additional Movie audio track to another existing movie. Yes, i have made some -slowdown via eac3to to make sure to have correct fps (23.976)

However when i have added it into audio editor to make proper start and ending, i have found that audio is not fitting the original timing in comparison with another audio dubbing which comes from the digital version.

I am pretty sure that this might be due to the VCRs RPM during the recording, as RPMs are not stable in analog VCR.


To better see what i mean is visible on this screenshot

https://i.ibb.co/DWcrHb0/pic-Audacity.png

- grey track represents example of the digital audio from DVD (i have minimalized other other multi-parts)
- blue track represents example of the digitalized audio from VHS tape

My questions:
- Is there a SW tool in which i can mark in both tracks some key points that represents same parts in both tracks a let the tool to fix it accordingly?
- What is the best practice to do manual adjustment of the entire audio track. I am afraid that simple cutting & shifting wont work because in the background of speech is also music or other noices. I am hoping for something like to select part of audio and let the tool to fix according the time line in the correct audio track..

At the moment for post process i use Audacity, but i can try another SW tools if they have something to better solve this problem

Thank you very much

Kind Regards,
M

[Skiller]

The obvious question first: are you sure it is the very same edit of the movie, frame by frame?
Assuming the actual capture was done right (without heavy audio stretching to keep sync, like VirtualDub does it if you don't use a TBC), a working VCR does not produce such a strong time compression and stretching. The drivetrain in VCRs is actually pretty accurate and self-corrects itself all the time – it has to be very accurate because otherwise TVs would lose sync and you would see just a rolling picture.

[vlp_007]

The obvious question first: are you sure it is the very same edit of the movie, frame by frame?
Assuming the actual capture was done right (without heavy audio stretching to keep sync, like VirtualDub does it if you don't use a TBC), a working VCR does not produce such a strong time compression and stretching. The drivetrain in VCRs is actually pretty accurate and self-corrects itself all the time – it has to be very accurate because otherwise TVs would lose sync and you would see just a rolling picture.

I am not an expert on this, just self learner. VCR is JVC HR-S7500 (no TBC, did not spent so much for model with TBC. But i hoped this one is middle range).
I did not seen any differences between VHS movie and the Bluray movie. If there are some specific frames or very little and very small parts , i dont know. Entire lenght is the same. Its not special edition, neither directors cut etc. Just Standard lenght

1/ Recorded via VCR and cable (white-red cinch <-> 3,5mm stereo jack) to mic input using Audacity. Format WAV, 44.1Khz. Then removed noise via noise reduction function (but i have both source version with noise and without... result was same in terms of drift)
2/ i have converted the WAV via eac3to.exe via "-slowdown" parameter to get the 23.976 fps, then loaded to Audacity both tracks (proper one and VHS wav) to compare.

As you saw on the screenshot, moving the VHS track left of right wont fix the sync.

I have had the same issue with previous task when i have recorded different movie audio and the drift started after 1h30m and and the end of the movie it was again synced OK. (of course i am speaking of the same fps as final movie)

Any advices on how to fix this as questioned in my initial post?

Thank you

[Skiller]

1/ Recorded via VCR and cable (white-red cinch <-> 3,5mm stereo jack) to mic input using Audacity. Format WAV, 44.1Khz.

That might be one of the issues. With no video to lock onto, the audio isn't synced to anything and runs at whatever audio clock your (motherboard?) uses. I think you absolutely need to capture both video and audio, even if you do not intend to use the video part. The video part is still needed to lock the audio to it and to see if there really are no differences between the two video tracks (VHS vs. Blu-ray). Also, if there are, it is much easier to spot the exact locations and possibly correct them.

The mic input (red) is wrong for this type of audio capture, the correct one to use is called "Line-in" and is usually the green one. While not related to the sync issue, as a side note, video uses a sampling rate of 48 KHz, avoid 44.1 KHz for video applications.


Looking at your screenshot we are talking about an offset of several seconds too late and then too early, all within about just one and a half minute.
That means if you were to manually correct this using time stretch it is surely going to sound awful.

But if we look closely at around 1:33:57 it does seem like that's were there either was an edit or maybe some capture or playback related issue.

In my opinion, to have any chance of successfully synching this up, you need to capture this with video.

[vlp_007]

1/ Recorded via VCR and cable (white-red cinch <-> 3,5mm stereo jack) to mic input using Audacity. Format WAV, 44.1Khz.

That might be one of the issues. With no video to lock onto, the audio isn't synced to anything and runs at whatever audio clock your (motherboard?) uses. I think you absolutely need to capture both video and audio, even if you do not intend to use the video part. The video part is still needed to lock the audio to it and to see if there really are no differences between the two video tracks (VHS vs. Blu-ray). Also, if there are, it is much easier to spot the exact locations and possibly correct them.

The mic input (red) is wrong for this type of audio capture, the correct one to use is called "Line-in" and is usually the green one. While not related to the sync issue, as a side note, video uses a sampling rate of 48 KHz, avoid 44.1 KHz for video applications.


Looking at your screenshot we are talking about an offset of several seconds too late and then too early, all within about just one and a half minute.
That means if you were to manually correct this using time stretch it is surely going to sound awful.

But if we look closely at around 1:33:57 it does seem like that's were there either was an edit or maybe some capture or playback related issue.

In my opinion, to have any chance of successfully synching this up, you need to capture this with video.

As for capturing the audio with video. How to make sure that during capturing i wont have big AVI (etc. format) from which i will have to again extract the audio itself. Is there any SW tool that can grab separately (independently) grab the video to video file and audio to audio wav file and keeping them synced? Is this too much to want?

Currently i do not have good capture card. As is 2021, this is challenge to find something fine. e.g. https://www.avermedia.com/professional/product/c725b/overview
However due to the microchip issues and other part issues they are not available on the market at the moment and delivery times are not guaranteed. I have tried to order it 2x times and i had to cancel my orders when the reseller called and said sorry. ETD is 4-6 months minimum

what do you recommend? Find old graphic card (brand / model) with SVIDEO input, but they do not have by standard also audio line ins.

As for the mic input: i know, i am aware that mic input is VERY sensitive. I have previously saw some YT videos recommending it. My mistake

[vlp_007]

1/ Recorded via VCR and cable (white-red cinch <-> 3,5mm stereo jack) to mic input using Audacity. Format WAV, 44.1Khz.

That might be one of the issues. With no video to lock onto, the audio isn't synced to anything and runs at whatever audio clock your (motherboard?) uses. I think you absolutely need to capture both video and audio, even if you do not intend to use the video part. The video part is still needed to lock the audio to it and to see if there really are no differences between the two video tracks (VHS vs. Blu-ray). Also, if there are, it is much easier to spot the exact locations and possibly correct them.

The mic input (red) is wrong for this type of audio capture, the correct one to use is called "Line-in" and is usually the green one. While not related to the sync issue, as a side note, video uses a sampling rate of 48 KHz, avoid 44.1 KHz for video applications.


Looking at your screenshot we are talking about an offset of several seconds too late and then too early, all within about just one and a half minute.
That means if you were to manually correct this using time stretch it is surely going to sound awful.

But if we look closely at around 1:33:57 it does seem like that's were there either was an edit or maybe some capture or playback related issue.

In my opinion, to have any chance of successfully synching this up, you need to capture this with video.

I still think about this "..and runs at whatever audio clock your (motherboard?) uses". Any meaning behind it? Is there really some mechanism that VCR audio sync could be linked to PCs motherboard? What does it mean.

Isnt Audio already synced while playing a tape inside VCR, and it should go out of the video synced?