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[Help] Fixing drift when syncing audio
#1
I want to sync an audio track from a VCD to a DVD. Both are 25fps.

The duration is near indentical except the VCD audio has a longer intro. Taking this into account there is about a minute difference.

If I sync the beginning of the movie, the VCD audio drifts and falls behind the DVD one.

I’m not sure this is due to PAL/NTSC since both are seemingly PAL 25fps, but there is obviously a speed difference.

Any tips on how I would go about syncing?
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#2
Probably you have checked this, but... maybe there is some missing frames in one (or both); it happens sometimes, especially at reel change (every 20m or so); try to check sync every, let's say, five minutes; if they are in sync in a step, and not in the next one, a missing frame (with related missing audio) should be there!
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#3
I've synced quite a few LDs now and the drifting is very common with both digital and analog tracks. There are two basic ways to sync, one is by matching video frames, and the other is by matching waveforms. I'm not able to capture video at the moment, so I do waveform matching with Cockos Reaper. You basically drop both mixes into separate channels, line them up at the beginning, and then play it. When it starts to drift from your reference track and you hear echoing you split the track and readjust it to match back up. It can vary wildly between titles, like I just synced Summer Rental and it never drifted more than 5ms every few minutes, but now I'm syncing Return of the Living Dead 2 and it drifts like crazy every 30 sec (not to mention missing frames or extra frames where you will have to cut out or patch in audio). It's not impossible to sync, it just takes way more time since you need more splice points.
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#4
Yeah I’ve had to fix missing frame and minor drifting before. I’m doing exactly as you say and matching waveforms using Audacity.

But for this particular movie, within a few minutes it’s alreasy drifting by a second or two. That sounds like more than missing frame right?

I even tried converting the audio as if it was NTSC -> PAL but that makes it too fast.

I was reading about sample rates. DVDs use 48KHz while VCDs use 44.1KHz. Would resampling effect speed and pitch?
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#5
If its a different master its definitely possible. I've noticed at the end of shots they will sometimes cut a few frames between masters, which can mean going off track pretty quickly. The sampling rate shouldn't effect it that much, both rates are based on the amount of samples in one second of time. A higher sampling rate will allow higher frequencies to be captured, but it won't change the actual pitch of the sound.
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#6
(2019-02-15, 06:44 AM)bronan Wrote: I've synced quite a few LDs now and the drifting is very common with both digital and analog tracks. There are two basic ways to sync, one is by matching video frames, and the other is by matching waveforms. I'm not able to capture video at the moment, so I do waveform matching with Cockos Reaper. You basically drop both mixes into separate channels, line them up at the beginning, and then play it. When it starts to drift from your reference track and you hear echoing you split the track and readjust it to match back up. It can vary wildly between titles, like I just synced Summer Rental and it never drifted more than 5ms every few minutes, but now I'm syncing Return of the Living Dead 2 and it drifts like crazy every 30 sec (not to mention missing frames or extra frames where you will have to cut out or patch in audio). It's not impossible to sync, it just takes way more time since you need more splice points.

I've had that problem many times also. It's why I still haven't finish Dawn of the Dead. I was half way through the movie with 200 edits and it wasn't PAL or time compressed. Very tedious work.
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#7
(2019-02-15, 06:40 PM)PDB Wrote: Very tedious work.

Yep. I'm beginning to accept that I will have to go through the entire movie with a fine tooth comb!
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#8
(2019-02-15, 07:56 PM)NeonBible Wrote: Yep. I'm beginning to accept that I will have to go through the entire movie with a fine tooth comb!

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#9
(2019-02-15, 12:31 PM)NeonBible Wrote: I was reading about sample rates. DVDs use 48KHz while VCDs use 44.1KHz. Would resampling effect speed and pitch?

The difference in sampling rate is not the cause of the drift.
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#10
I suppose in those cases, working from the video master will help you sync better because you can point out the missing frames in any place whereas with audio you're kinda blind. Also when the sync echoes doesn't mean there's a frame difference it can sometimes just mean the sources weren't running at the exact same speed, but on screen, you wouldn't notice.

So when you align the sync so that they match exactly, you are messing up with the rest of the sync along the line. The further you cut out ms to match, the further it goes out of sync further. You need video to be absolutely exact, and not bother that every line doesn't echo.

This from my experience syncing the Terminator mono tracks.
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