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Dual System Sync Drift +GUI Problems: 5Dm2+FCP Crazyness

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Daniel García
Dual System Sync Drift +GUI Problems: 5Dm2+FCP Crazyness
on Aug 23, 2011 at 1:26:51 am

Hi, I'm syncing audio for a feature shot on Canon 5Dm2 and 1Dm4 cameras and I'm having drift problems that I can't find a fix for. I'm looking for similar threads on this forum, but strangely enough, I can't find anyone with my problem.
Audio was captured on a ProTools laptop with an M-Audio Profire 2626 firewire interface, and sometimes a Tascam DR-100.

I've read Matt Lyon's tutorial and Bruce Sharpe's blog post, which both seemed to agree that having the right sequence settings before importing audio without timecode is essential. I've been working with a 23,976p preset which matches my video footage. I bring both audio and video to a temporary sequence, sync both internal (which is an average of 2 frames early) and external audio with the clapperboard marker with sub-frame accuracy, and when I look at the end of the take, the external audio is a couple frames late by minute 5, which is noticeable.



What really gets crazy is when I start over and import the audio with a real 24.0 fps timecode sequence preset.
The drift seems to be even less...

But you can clearly hear double hits and a delay between the two tracks. When you zoom IN a little more...

The external audio snaps out of sync to where it really sounds. The GUI was lying!

I'm trying to force different timebases for the audio material but none of them seem to work right, those two behaviours seem to persist depeding on the ntsc TRUE or FALSE tag FCP applies according to page 97 of the xml documentation.

It seems that when importing with a proper ntsc=true timecode the correction to avoid drift is a speed change somewhere between 100.02% and 100.03%. But I can't use this "hack" because I'm making heavy use of multiclips and that's incompatible with speed changed clips.

Is there any expert who might help me? What am I doing wrong? Is this a hardware or software problem? Do I need to ask my audio guy to pre-process all of his files with that speed change or is there a FCP setting I'm missing?

Thanks for any help


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Bruce Sharpe
Re: Dual System Sync Drift +GUI Problems: 5Dm2+FCP Crazyness
on Aug 23, 2011 at 2:53:22 am

There are two possibilities: 1. there is sync drift in the original recordings, and 2. the FCP settings are not right. If #2 is the problem, then the correction factor will be 100.1% which is larger than you are seeing, so it's best to rule out #1 first.

With regard to #1, it will be hard to determine this inside FCP because of the subtleties of #2. Instead, pick a video clip that overlaps the audio recording by a fair amount and, using QuickTime Player or otherwise, export the audio from the video clip. Bring that audio and the external audio into a multitrack audio editor (Audacity, SoundTrack Pro, ...) and line up the two audio clips by hand. Does the external audio stay in sync? If not, you need to do some time stretching to remove the error.

But if the sync looks good, you need to tackle #2. Note that you cannot adjust the NTSC tag value in XML and have it stick after importing into FCP. The only way to ensure that you get the right NTSC values is by following the procedure in the blog post you mentioned earlier.

Bruce Sharpe
Singular Software Inc.

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Daniel García
Re: Dual System Sync Drift +GUI Problems: 5Dm2+FCP Crazyness
on Aug 23, 2011 at 4:38:40 am

Wow. First reply and it's from Mr. Sharpe, what more could I ask for? Thanks.

I've tried both syncing the same files in Premiere CS5 and a QT7-> AIFF export as you suggested on Soundtrack Pro and the results seem conclusive. There's a delay of 1.5-2 frames in 5 minutes, so a correction around a 100.02% speed is needed. It doesn't sound like much, but on 8 min clips it becomes really noticeable.

I was aware of FCP's sequence settings woes from the beginning and had set it up right before the project start. I was only messing around with alternatives in panic. So I'm back to talking to my audio guy again.

Anyways, does anyone know what was up with that GUI glitch? The audio waveform was drawn in the right place only in the last two zoom levels. Talk about a "Pro" app.

I've read other threads where people correct those errors with Compressor... I guess that'll be faster than Pro Tools, but will it lose much quality comparatively? Any recommendations?
Will my correction be constant among all clips, or will each clip need a different amount of correction? That'd really throw a wrench into my workflow right now...

Anyways, thanks to all answers.


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