Audio from Zoom not in synch with camera audio

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percoplus

Active member
I am editing a video of a music concert. I have camera footage with audio. Someone handed me a separate audio file recorded with a Zoom H4, but when I got it onto the timeline it is out of synch. It as if it recorded at a different pace. What went wrong? How do you fix such a thing? I spent a while going through and shaving off frames every several minutes or so, but there has to be a better way.

The only thing I can tell is that it was recorded at 44.1kHz while my audio is at 48.
 
percoplus said:
The only thing I can tell is that it was recorded at 44.1kHz while my audio is at 48.
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There's the first part of your problem. Convert the original 44.1kHz audio to 48kHz before editing.

Second, you're using a sound file that was recorded completely non-sync. There will be some drift over time, that's just a part of the process. You can use time compression/expansion on the audio, or create a speed adjustment on the video. The idea is to note sync points at the head and the tail, calculate the drift, and adjust accordingly.
 
One other thing. You didn't say what the video was shot on. If it was a DSLR then there may be other issues. Probably it's either the sample rate or just plain drift.
 
Canon XHA1s audio recorded 16 bit 48 kHz. The Zoom was not mine - it was the older H4 model and I guess has a known issue with drift
 
C2V said:
There's the first part of your problem. Convert the original 44.1kHz audio to 48kHz before editing.

Second, you're using a sound file that was recorded completely non-sync. There will be some drift over time, that's just a part of the process. You can use time compression/expansion on the audio, or create a speed adjustment on the video. The idea is to note sync points at the head and the tail, calculate the drift, and adjust accordingly.
Click to expand...

In sort of an unrelated topic, the issue of 'respeeding' 25 fps to 24, that it was 'better' to go from 25 down to 24, rather than from 24 up to 25, because of phasing errors in stereo channels.

Not that I do any 25 fps... but wouldn't resamping at 48K have a similar affect on material that was recorded at 44.1K?

Alternatively, there's no problem with 'upresing' from 24 to 25 fps, relative to slight changes in the audio sample rates.
 
Resampling from 44.1kHz to 48kHz isn't a big issue. Most sample-rate conversion is going to introduce minor artifacting, though it's pristine if down-converting from a perfect multiple (like 96kHz to 48kHz).
 
j1clark@ucsd.edu said:
In sort of an unrelated topic, the issue of 'respeeding' 25 fps to 24, that it was 'better' to go from 25 down to 24, rather than from 24 up to 25, because of phasing errors in stereo channels.

Not that I do any 25 fps... but wouldn't resamping at 48K have a similar affect on material that was recorded at 44.1K?

Alternatively, there's no problem with 'upresing' from 24 to 25 fps, relative to slight changes in the audio sample rates.
Click to expand...

It's a bit misleading to start talking about audio and frame rates since audio doesn't run at a frame rate. You are actually talking about switching between film speed and video (PAL) speed. The footage is undergoing a frame rate conversion the sound is just getting slowed down or sped up. It's a small but important distinction because you can change frame rate with out changing speed (29.97 to 23.98) and you can change speed with out changing frame rate (doing slowmo with frame doubling).

Either way you shouldn't have any channel phasing. If changing the speed of the file causes channel phasing it's time to get a different plugin/ software etc.

It's also a weird scenario. You would only need to go 24 > 25 in making a PAL version of a film footage, and the only reason (I can think of) to go 25 >24 is to film out your PAL video footage. I can't think of any situation where you could use either to do the same thing so it wouldn't be a choice.
 
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