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Audio problems after compression

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Wil Magness
Audio problems after compression
on Nov 8, 2010 at 6:53:13 pm

I am not sure if the problem is in Compressor or FCP.

First, using "Send to Compressor" I compressed a 1 hour sequence using the "DVD 90 Minutes Best Quality" settings creating an MPEG and a Dolby Digital file.

The video came out fine, but about half way through the final sound file, the audio cuts out and there is complete silence for the rest of the file. I retried compressing a few times and got the same result with slight variations.

I went through the FCP sequence and replaced a number of MP3 files with AIFs because I read that the embedded compression could cause problems but this did not fix it.

I then exported the sound as an AIF from FCP and, using Compressor, tried to create the Dolby Digital file again. This time all of the audio is there, but around the same place there is a very loud crunchy/static/beeping sound that lasts about 30 seconds. The rest of the audio is fine.

The sequence I am working in has many audio tracks due to the fact that we overdubbed most of the movie and inserted tone and sound effects. Most of the files are AIFs, but some of them are WAVs. Could this be the problem?

Going through the whole movie and converting all of the files to AIFs and replacing them would be a huge project, so I'm not eager to do that. If anyone has any idea what may be causing this, I would be very interested.

I am using:

FCP 7
Compressor 3.5

On a 15" MacBook Pro


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Chris Borjis
Re: Audio problems after compression
on Nov 8, 2010 at 10:04:22 pm

maybe try deleting all the audio renderings in the project folder, then
export again as an .aiff



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Dave LaRonde
Re: Audio problems after compression
on Nov 9, 2010 at 7:30:08 pm

[Wil Magness] "I went through the FCP sequence and replaced a number of MP3 files with AIFs because I read that the embedded compression could cause problems but this did not fix it.... Going through the whole movie and converting all of the files to AIFs and replacing them would be a huge project, so I'm not eager to do that."

Sorry to hear it's too big a job for you. Unfortunately, if you don't you'll probably continue to have audio woes.

Why?

YOU DON'T USE MP3 FILES IN FCP. It's a tough lesson to learn, but I doubt you'll make the same mistake twice.

So you have a choice: replace the mp3's and you'll have good audio. Don't replace them and take your chances.

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


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Wil Magness
Re: Audio problems after compression
on Nov 9, 2010 at 8:38:43 pm

Sorry, I miswrote originally. I replaced all of the mp3s. I meant to ask if I should do the same with .wav files or if they\'re okay.

In any event, I believe I\'ve resolved this situation. My sequence was set to 48 kHz while most of my audio was 44.1 kHz. I switched the sequence setting, rendered again and it appears to be fine.

I still have some random 48 kHz audio clips in the sequence, but there is no noticeable distortion (yet, I haven\'t watched the full DVD)

I read in the fcp manual that it was better to have 44.1 kHz audio in a 48 kHz sequence than the opposite, but could it be that that only applies when the majority is 48 kHz? I definitely have a majority of 44.1 kHz.

At any rate, thanks for your help! These forums are great!


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Dave LaRonde
Re: Audio problems after compression
on Nov 9, 2010 at 9:36:52 pm

[Wil Magness] "I meant to ask if I should do the same with .wav files or if they\'re okay."

Thanks for the clarification. I have to tell you, I won't be much help. Since I began using FCP, I've always used aiff files at 48k, at either 16 or 24 bit. I've never had any audio problems, so I haven't experienced your problems.

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


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