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audio sync issue with DSLR workflow?

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Jeremy Dehn
audio sync issue with DSLR workflow?
on Feb 29, 2012 at 10:33:45 pm

So I have a very slight amount of audio drift--about one frame every 10 minutes--when I sync my Canon 60D (1080p 24) footage with audio recorded on a Tascam DR-100mkII (24-bit, 48K WAVs).

I know that's very little, but I'm still wondering whether that's normal. I'm new to double system with DSLR's, and I suspect I'm overlooking something.

My workflow:

* took previous Cow advice and made sure easy setups were a default of 23.98 before I started

* ingested video via the Canon plugin to ProRes422

* imported audio using the file menu, rather than just dragging it in

Noticed the problem because I ingested the camera's scratch track so I could verify sync. When I lay them on the timeline, audio and video start in sync, but an echo is noticeable by 3-4 minutes in, and waveforms have drifted off by about a frame at the 10 minute mark.

The audio is slower by that one frame per 10 min, meaning if it's in sync at 1:00:00:00, then at 1:10:00:00, I have to move the audio clip back one frame to make it in sync again.

Am I just being too anal-retentive here to expect perfect sync out of this equipment? Or have I done something wrong?

(FCP 6.0.6, Mac OS 10.6.8.)



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Michael Gissing
Re: audio sync issue with DSLR workflow?
on Feb 29, 2012 at 10:40:47 pm

Did the Tascam record broadcast wav files? If so was the timecode 24 or 23.98 (23.976 actual).

Try this solution that worked the other day for broadcast wav files with the wrong time stamp. You can test one one file before changing all the files

http://forums.creativecow.net/readpost/8/1154445

Another trick is to change the speed of the audio. Open up the varispeed box and change the audio speed to 100.1%. My guess is that the timing difference is between 24 and 23.976 which is .1% . This is a cheat rather than a proper fix. Again if you try it on one file it will tell you the problem is the tiny difference in frame rate.


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Jeremy Dehn
Re: audio sync issue with DSLR workflow?
on Feb 29, 2012 at 11:20:34 pm

Yeah, I thought it might be that 23.976/24 deal too, but I played with 99.9% and 100.1%, and that made the sync worse. Mathematically the difference between 23.976 and 24 should mean I'm off by a frame every 1000 frames, shouldn't it? And I'm off more like one frame every 14,400 frames.

I also just tried the modify/timecode deal, but none of the TC boxes were checked at all, I'm assuming because these are plain wav files, and there is no timecode assigned to them until they're imported into FCP. They don't show a frame rate at all even in the FCP browser.

Any other ideas? I wonder if it's just a consequence of variable bit rate compression that sync might be off?



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Jeff Meyer
Re: audio sync issue with DSLR workflow?
on Mar 1, 2012 at 12:10:28 am

This is what you get with asynchronous sources. If you were syncing camera and the audio recorder they would have the same timecode coming from the same clock. With a 60D there aren't any timecode sync options, so you'll have to accept that the sync may float a bit due to variances in the clocks on these two devices. The best you can do is try to find a silent moment to re-sync every minute or two.


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Michael Gissing
Re: audio sync issue with DSLR workflow?
on Mar 1, 2012 at 1:25:19 am

I would expect any modern device to hold sync over ten minutes. What really matters is frame rate versus sample rate - both are controlled by crystal sync generators which these days should be more accurate than that.

When FCP gets it wrong it is nearly always an issue of wrong stamping of frame rate so if the .1% isn't it then I can only conclude that there is a fault with the sync accuracy of either the camera or recorder.


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