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Audio Sync

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Elliot Beach
Audio Sync
on Feb 26, 2013 at 12:44:25 pm

Hi there.

I have a small issue (I hope). I recorded some footage on a DSLR and used a laptop and external mic to recorded the sound using Audacity.

Problem was Audacity by default records at 44.1 Khz, so all my audio is that in Audacity. So when it goes into the time line which is 48Khz it slowly drifts out of sync.

If i change the audio to 48Khz and export and then add that to the time left it plays must faster and also goes out of sync.

Is there a way to fix this??!


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Nick Meyers
Re: Audio Sync
on Feb 26, 2013 at 7:09:35 pm

first thing is that it may not be the sample rate that is the issue.

check your sequence presets in FCP (in A/V settings)
are they the same frame rate as your current project?
if not, that can cause audio drift.

to fix, check the correct sequence preset, & r-import the audio.
sometimes you have to import into a new project,
or change the file names before you import. (FCP "remembers" the files)

if it IS the sample rate, then the simplest solution could be to change your sequence settings to 44.1 rather than 48k


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Dave LaRonde
Re: Audio Sync
on Feb 26, 2013 at 9:45:12 pm

If you KNEW that Audacity records at 44.1 kHz, and you KNEW that FCP likes its audio at 48 kHz, why did you not do the conversion in Audacity or some other audio application before you started work in FCP?

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA

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Michael Gissing
Re: Audio Sync
on Feb 26, 2013 at 10:50:45 pm

Audacity does an excellent sample rate conversion. Do the 48k convert in Audacity and then reimport new files with slightly different names once you have checked your settings as Nick outlined. Also make sure your bit depth is 16 or 24 bit only. FCP doesn't like 32 bit or float

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Elliot Beach
Re: Audio Sync
on Feb 27, 2013 at 1:34:35 am

Hi, thanks for the replys.

Great that sorted it. Changing the whole Audacity project settings to 48Khz and exporting didn't change the speed (as it would do when I changed them individually for some reason) and also settings it to 24-bit. Then re-importing to FCP with all the corresponding FCP project settings set at the start and its all good.

Thanks, that was a lot simpler than I thought :)
Freelance DP & Photographer (LDN)

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Jean-Christophe Boulay
Re: Audio Sync
on Feb 28, 2013 at 7:46:34 pm

Hi Elliot,

The problem you were having with your files speeding up when changed to 48kHz is that you were not converting the sample rate, only changing it. I haven't used Audacity enough to point to where you made the mistake, but the result you describe is pretty clear cut.
In some software, it is a bit too easy to export material at a different sample rate without conversion. This affects pitch and duration, as the same number of samples is being played back on a different time base. When going from one sample rate to another, it's good to look for the word "conversion". That's an assurance the operation will create the missing samples or drop the superfluous ones.

It's the audio equivalent of the difference between adding pulldown or conforming in Cinema Tools to change video frame rates.

JC Boulay
Technical Director
Audio Z
Montreal, Canada

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