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Imported audio time difference 29.97 vs 30

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Jay Heinz
Imported audio time difference 29.97 vs 30
on Jun 23, 2011 at 9:59:00 pm

I'm editing a 30 minute animated video in a 30 fps sequence w/ 48k audio. I just got the score from our composer, which was 48k as well, and when I imported it in, I noticed some audio slip - about 2 seconds in total by the end of the piece. After a lot of back and forth, I tried importing the audio into a 29.97 sequence and it ended up being about 2 seconds longer. So:

29.97/48k - length of score 28:21:17
30fps/48k - length of score 28:19:25

Shouldn't the audio stay the same length if it's the same khz? Why would the frame rate effect the audio? And what do I do in this situation? I've got VO, sfx, and video set up in a 30fps sequence. Is there a way I can force the score to be the correct length?

thanks,
Jay


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Dave LaRonde
Re: Imported audio time difference 29.97 vs 30
on Jun 23, 2011 at 10:30:58 pm

[Jay Heinz] "I'm editing a 30 minute animated video in a 30 fps sequence w/ 48k audio."

Why is that? Why aren't you editing in a 29.97 fps edit timeline, which is the correct frame rate for NTSC television, DVD's and Blu-Ray?

It makes a difference.

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


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Jay Heinz
Re: Imported audio time difference 29.97 vs 30
on Jun 23, 2011 at 10:51:04 pm

It's for a planetarium show. We use 30fps. I understand the difference between drop and non drop frame in regards to video but why would that effect the length of an imported .wav?


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Michael Gissing
Re: Imported audio time difference 29.97 vs 30
on Jun 23, 2011 at 11:23:39 pm

Probably because your default project is set to 29.97 so FCP stamps that as the timecode rate which makes it drift in a true 30fps sequence.

The other explanation is that the composers sequence was running at 29.97, as few audio sequencers run at true 30 fps.

Read this (second half in particular) to see if it is a problem with your audio import.

http://library.creativecow.net/lyon_matt/fixing-fcp-assets/1

If not then the answer is to change the length by .1% which is too small to affect pitch. A quick and dirty way to check if this is the problem is to varispeed the audio in FCP to 99.9%


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Jay Heinz
Re: Imported audio time difference 29.97 vs 30
on Jun 24, 2011 at 5:40:32 pm

I looked in the XML file - everything is set to 30fps. It seems like a dirty hack, but changing the length by .1% did the trick and you're right, I didn't notice the pitch change at all. Thanks for the help.


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Michael Gissing
Re: Imported audio time difference 29.97 vs 30
on Jun 25, 2011 at 3:26:55 am

In your case, the issue is likely to be that your sound post guy had to run at 29.97. So real time was lost and a small vari speed was needed.

Doing it in FCP is quick way to check if that is the issue and which way to go. A better way is to run the audio through any number of audio programs or even Compressor and bake in a vari speed so your file is correct without doing the FCP cheat.

An alternative would be to export an aif mix down of your sequence as a master audio.


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