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I have a bizarre sound synchronization problem which I am really puzzled with.

I recently recorded an interview with the video camera capturing the sound of the interviewed and an external sound capture for the interviewer.

When editing it with Adobe Premiere CS6 I started by synchronizing the start of the interview since both recordings started a few seconds apart. So far so good.

Then, one of the recordings was lagging and at the end of the recording (lasting around 25 minutes) where I found a delay of more than one second on one of the sound tracks. So I found a sync point and used the rate stretch tool to adjust one of the tracks to match the other and since beginning and ending were synchronized (I checked) all was fine... Or at least so I thought.

When I started editing further I realised that towards the middle of the recordings there was further de-synchronization. It is like the lagging and speed-up of sound is non linear; like an accordion...

Has anyone experienced this before? What causes it? How can it be corrected other than cutting everything in smaller chunks and adjusting them one by one?

Thanks in advance for any help.

PS: I had posted this same question on Video Production beta but decided to repost it here since it relates more to sound than to video.

  • could you add more information on used samplerates (camera, premier, recorder), sync protocol (used between recorder and camera). Is the 'rate stretch tool' part of Premiere or are you using a DAW? – Arnoud Traa Apr 10 '14 at 10:18
  • Did you record your audio in 44.1 or 48? What recorder did you use? – Edwin Matthews Apr 10 '14 at 11:35
  • This question appears to be off-topic because it is more video production oriented as the problem is most likely related to a video issue. Please don't post the same question on multiple sites. – AJ Henderson Apr 10 '14 at 14:07
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    i don't think this is really off topic. these are common issues, see the explanation by georgi. valuable information. – Arnoud Traa Apr 11 '14 at 7:49
  • equipment information would be a lot more helpful for us to know. if perhaps you were using an analog tape recorder, the lagging and speed up of sound could also be attributed to power issues affecting your motor. This problem however wouldn't be unique to digital audio recorders. – user6513 Apr 11 '14 at 17:07
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Do expect drift between non-timecode-locked equipment. This is common. One way to get around it is to feed the sound from your recorder back into the camera, monitor via the camera's audio/headphones out, then use the sound from camera in your edit. Lots of cables, but fewer posts on forums later if you don't run across other complications.

Sync drift can also happen e.g. on guerrilla shoots where camera only shoots at 24p but the picture editor then reinterprets the footage as 25p, so the sound is off by 1 frame every 1 second (expect this with kit imported across US/EU borders).

Modern stretch tools (for both audio and video) can do a good job, but I wouldn't trust a computer with footage that long. I find an edit pass gives me some fatigue but overall fewer headaches.

You can also directly hack a different sample rate into a WAV file's header and then resample on import (much like pitch-shift, only we're talking fractions of a percent). I've done this with a line-in recording through audio interface vs file from recorder, which needed sample rates of 48000 and 48003 to sync perfectly (and some math to determine the drift). Soundhack does this on OSX.

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    To add on to this, even if your recording at the same sample rate the 2 machines (camera and audio recorder) will naturally drift if they don't have a common sync reference like black burst. Quick takes it usually isn't noticable but on a take 25 minutes long they are bound to get offf track – coaxmw Apr 10 '14 at 14:52

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