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Audio Sync Issue on the rocks, with a twist

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Sarah Manschot
Audio Sync Issue on the rocks, with a twist
on Jul 19, 2013 at 10:40:00 pm

Hi there,

Okay first off I have read a TON of posts about this issue and it is still not solving my problem, just so you don't think I am asking without any previous research!

In FCP 7 I am editing a feature shot in 24 (film), converted to HD Quicktime files and then compressed to Pro Res 422 LT 23.98 frame rate for editing (My frame rate in Easy Setup is 23.98, my Sequence Preset is 422 LT 1920x1080 24p 48...there is no option for 23.98 but when I look as Sequence Settings it says my editing time base is 23.98) . My audio was shot at 44 and has been converted to 48KHz AIF files through Quicktime Conversion as this is what FCP likes. The thing is, the sync starts out perfectly and then drifts over time, even just ever so slightly, but it's noticeable. The sound comes out just before the actors are speaking, not after.

Here's what I've done that HAS NOT worked:
Made sure my sequence settings and Easy Setup are both set for default 23.98 (then closed FCP, opened a new project, imported the video and audio again, as in imported the audio from a different source so it wasn't the same clip that may have been time-stamped the first time) = drift
Pulled down my audio 1% = drift
Converted the frame rate of the audio to 23.98 in Wave Agent = drift

The only thing that HAS worked is playing the 48KHz audio back at a speed of 99.9%. I'm not sure if this is good practice or not, as I would rather just have it work! (I was initially editing in 24fps and the 48KHz audio synced beautifully, but as I am not going back to film and it's quite early in the editing process I have switched to editing in my final format now, which is 23.98). I've read about how FCP has trouble with frame rates of audio (I understand I shot the project in 24 but the digital files have been converted to 23.98) but under Modify, Timecode I have the Source TC unchecked.

Can someone please give me some feedback here? I've read the Fixing Assets in FCP using XML Tutorial by Matt Lyon already, but I have no green bars above my audio at all, until I change the speed to 99.9% of course.

If someone could please help me out I would be so grateful! Just wondering if I am doing something wrong here or if I now have to change the speed of all of my audio files and if this will affect my project at the end?


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Michael Gissing
Re: Audio Sync Issue on the rocks, with a twist
on Jul 23, 2013 at 12:22:19 am

You have slowed your video by .1% so that is why you have to change the audio speed. Broadcast wav audio with timecode does have an embedded frame rate but in real time terms what you are doing with Wave Agent doesn't alter the length, just the metadata.

So you have to resample the audio from 48000 to 48048. This will then play in FCP at the correct speed. Either that or process the audio with a -.1% varispeed and use the new files to sync with. You might be able to do that as a batch in Compressor.

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Miranda Brownlee
Re: Audio Sync Issue on the rocks, with a twist
on Jul 30, 2013 at 3:19:34 pm

Thanks for your response! I handed my files over to an audio tech with Pro Tools, he did the pulldown and now it syncs perfectly. Whatever I was doing with the attempted pulldown just wasn't right.

One more question: my original audio was recorded as 44KHz 24 bit. I changed this to 48KHz 16 bit before I handed it over to my audio editor for pulldown. Now I'm wondering if I should have switched it to 48KHz and kept it 24 bit. I am hearing different things about editing at 24 bit vs 16 bit, AKA my final output will have to be 16, but I'm not sure if I should be switching now or later, after the final mix. Any feedback? This is for a feature film FYI, so I am not looking to sacrifice quality at any level.

Thanks again.

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