How do I resolve audio drifting?

H

HeyAndy

Active member
I imported a test audio recording from the Zoom H4N into final cut express and synchronised it with my test footage. But after a couple of minutes of play time the audio starts to drift and doesn't match with the rest of the video.

I was wondering what I can do to avoid this? What settings should I make on the Zoom H4N/final cut in order for both sound and video to be in synch?
 
For starters, you aren't going to avoid drift completely since you're working with non-sync audio. It's just going to happen, and Zoom is one of the worst for this. It's usually not an issue for narrative where the individual takes are shorter, but longer takes (generally over 10 minutes) start to get out of sync. I do not have any issues even with 12-minute clips and audio from my FR2-LE.

That said, you should have your recorder set to WAV, 24-bit, 48kHz. FCE runs at a native 16-bit/48k.

You'll likely still see drift, and the are a couple ways to correct it if you have to use longer takes. Find a mutually-identifiable out-point (something you can easily find in both audio and video), then time-compress either the audio or the video to match the out points. For future shoots, use both a head and tail slate for this.
 
Keep in mind, yes the Zoom has issues, but if you were shooting on any camera without stellar sync crystals......the camera is also to blame. Long takes are the bane to indie production when separately recording for post-sync and using a DSLR......it just comes with the territory. Shoot accordingly (shorter takes). Otherwise, you need to upgrade on both aspects........camera and audio sides.


If you get a recorder with reliable TC clocking, but continue to shoot on a dslr........same problem. Buy a camera that has TC master out.....but don't have a recorder that will slave and sync.......same issue. Plan accordingly....and you will be okay.

Always love the "it's the audio gear" threads.
 
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Note that it is frequently less noticable to diddle the video and leave the audio intact. Changing the speed/duration of audio tracks is much more prone to cause ugly audible artifacts. But few people notice dropping (or duplicating) a single frame of video from time to time.
 
Richard Crowley said:
Note that it is frequently less noticable to diddle the video and leave the audio intact. Changing the speed/duration of audio tracks is much more prone to cause ugly audible artifacts. But few people notice dropping (or duplicating) a single frame of video from time to time.
Click to expand...

:thumbsup:

Good point :thumbsup:
 
The two usual ways to deal with drift (from the sound side) are to time stretch or to resync periodically.

Stretching is not generally used unless the drift is because of a speed change as in a 3-2 pulldown that needs to be applied to the sound after a film to video transfer. If the drift is not completely stable the stretch won't work. More often is you adjust sync between lines.

BUT you are on the FC family so there may be a different issue. FCP (and probably express) will inherit settings from your capture settings even if you don't actually "capture" anything. So if your capture settings don't match your project settings you can screw up your project for importing sound. FC will assume that you have frame rate converted the video and procede to do the same to any audio you import. The "drift" in this case will be exactly 3 seconds per hour.

I don't think you can fix a project after you have started it with mixed settings (FC has stamped the clips with the wrong metadata). At least when we were figuring out this "bug" (Apple doesn't consider it a bug BTW) we never found a reliable way to fix it.

In my Noiz on Noise blog there is an entry on a work around that often works and a link to the tool you need to do it. Basically you tag all your sound files with incorrect metadata so FC doesn't feel the need to "fix" them. You could try it on one of your sound files and see if it does the trick. If it does then you are the victim of this (non) bug. You can then just do the same to all your sound files and import them and you should be good.
 
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