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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Audio Slipping at 24 FPS

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Gabriel C.

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Hi Guys,

Sorry if this has been covered. I looked around - probably could have looked harder.

I shot a feature a few months ago, and we're in the final stages of post ... we shot at 24FPS (not 23.98) and there seems to be an audio slipping problem when I bring our sound into Final Cut Pro. The sound recorded into camera is fine ... but all the sound done to picture and sent to me at 48K or 48.048K slips after a few minutes.

Does anyone know about this - and if so - is there a work around?

Thanks so much!!!
 
So you're saying the sound recorded on another system slips out of sync? Did they record at 48K?
 
Yes. The slipping has happened in two ways:

1st: When we shot the bulk of the movie, we recorded at 48K on a sound devices 744 (I think that's what it was called) ... it was fine in FCP for editing ... syncing all worked - and editing worked. Then we sent an OMF to our sound guy with prores422 at 24FPS ... he did an M and E and foley and everything - the OMF came in against the ProRes file slightly out of sync. He recompiled, and sent it back to us at 48K and then again at 48.048K (in case it was that .01% slip from 23.98 to 24) - He's done a bunch of movies - so I think we can rule out just being silly (IMHO). The thing is, apparently editing at 24FPS (as opposed to 23.98) is relatively rare. Is that true?

2nd: When we went to do reshoots, we recorded on a less awesome sound device (the tascam something) ... we always ran sound into camera. When the assistant editor locked the sound from the tascam with the sound from the red ... it would slip rather quickly. If I slow it down inside of FCP to 99.9%, it works.

There is some speculation that FCP is speeding up the 48.048 to 48 because it's assuming that's what we want.

When I take a 20 minute audio segment sent out of pro tools at 48K, 48.048K, they have different lengths in Pro Tools ... but THE SAME length in FCP. This is going to become an issue as we're doing our final assembles.

Any help at all would be MUCH appreciated.

THANK YOU!
 
Gabriel C. said:
Yes. The slipping has happened in two ways:
Click to expand...

What you are describing is NOT known as "Slipping" but DRIFTING. And it happens when there's a framerate mismatch between audio an video. Meaning that your workflow was flawed and whoever decided to run video and audio at a given frame rate didn't figured out the math right. Specially if dealing with several recording systems. I'm sorry for you...
 
I'm not sure if that's right. Everything works fine IN FCP - but when it leaves FCP and comes back in ... there's an issue. The audio recorded on set fits with the video and does not drift ... it's once it comes back in that it drifts.
 
Gabriel C. said:
There is some speculation that FCP is speeding up the 48.048 to 48 because it's assuming that's what we want.
Click to expand...

This is what we found was happening with our BWF files direct from the shoot on a feature last year.

If it plays back in sync in Protools and the duration of the video is the same; then perhaps you should just generate mixdowns and use them to master the film rather than trying to OMF back in to FCP.

Incidentally, how are you getting the OMF back in to FCP? Or am I misunderstanding you?
 
Gabriel, did you sort this problem out? I'm having the exact same issue.

I shot a short recently and edited in FCP with the sound and picture syncing, no problem. I sent the OMF to my sound guy with picture and everything sync'ed up on his computer. When he exported the sound back to me and I put it in the timeline in FCP it was out of sync..

I'm not that good with technical stuff but if you've sorted out your problem, could you let me know how you did it? Thanks.
 
We've experienced the same problem.

We fixed it by changing the speed of the audio file by 0.1% to 99.9% instead of 100%.

That worked, try it.
 
I was wondering if anyone can tell me what veresion of FCP this instance has occured on? A friend of mine who has experienced the same problems noted above had me try and problem solve this situation for him. He passed me the picture with original non mixed audio, and then the audio files. After placing them (various version of audio at 16, 24 and 32 bit) all in the timeline, they all fit perfectly with the original audio. There was no drifting what so ever and the waveforms lined up perfectly. My point being that I was unable to recreate the problem that was happening with the editor's he was working with. The only difference that I can gather between the editors facing the sync problems and the tests I conducted with his audio was the version of FCP. They are using 6.05, I am using 6.06. Any one of you experiencing the sync problems found this to occur with 6.06?
 
Final Cut has some weirdness in the true 24 FPS timecode area. Here's a thread explaining the reasons why: http://duc.digidesign.com/showthread.php?t=212057. A short work around is using AIFF's as deliverables instead of BWF (which will get rid of the TC metadata). From what I've heard it's JUST with true 24 and not 23.976. I'm curious as to why an HD project would be shot and cut using 24 FPS instead of the standard 23.976.
 
tom.boykin said:
I'm curious as to why an HD project would be shot and cut using 24 FPS instead of the standard 23.976.
Click to expand...

They aren't, but theatrical projects could (and indeed have been), in PAL countries where there's no benefit to running at 23.976.
 
There are countries other than America?!? What is PAL?
---Just kidding. Excuse my US-centric assumption, I was raised in the land of NTSC. But I should have asked which side of the pool first.
 
Isin't this an issue of 23.98 video and 29.97 audio? I'm about to head down a similar path. We have our cut at 23.98. I'm going to export omf and low-res picture to sound designer. He wants 29.97 since most bigger mix houses mix in 29.97 (even for 23.98 projects) Apparently, this is common, and you can lay the 29.97 mix back to 23.98 HD master with little issue.

Does anyone else have thoughts or experience with this?

Thanks!
 
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