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Old December 12th, 2007, 08:00 AM   #1
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Drifting tracks

My little girl is singing in a children's choir, and they twisted my arm to make a CD recording for them. I thought I did my homework - and still, I ran into a serious problem.

They use tracks for accompaniment, which I got on a CD. I remastered the CD adding a short 1KHz tone burst 3 seconds before each track begins for syncing purposes. I used an Alesis firewire mixer and Adobe Audition 2.0 for multitrack recording of five microphones.

I know now, I should have recorded the accompaniment directly onto a separate track right there... I thought I can add that in post. Well, I can indeed, the tone burst makes it easy to sync the beginning but then it drifts. I already suspected I'm going to run into this issue when Audition did not let me set the sample rate to 44.1 KHz (don't know why) - I chose the next step up, 48 KHz, I thought that will make it easy to give the audio to the video guys (another team was filming at the same time).

When I import the track, Audition warns me of the sample rate difference, so I upsample to 48 KHz. I will probably have to stretch/compress the CD track to bring it in sync... just my gut feeling.

Is there a set percentage of stretching or I have to experiment?

[Side question: why didn't Audition let me set the sample rate to 44.1]?

Thanks,
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Old December 12th, 2007, 02:44 PM   #2
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I'm not sure why you have to upsample if you recorded at 48k. That should be perfect for video if your video editing timeline is setup at 48k. If the sample rate is off then I might consider outputting the audio to an analog device and re-recording at the right sample rate unless you have a good time compression/expansion plug. A bad plug will leave artifacts. As far as, the audition session not changing sample rate...I haven't a clue.
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Old December 13th, 2007, 06:43 AM   #3
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I don't have to upsample the actual recording I made, but the tracks (accompaniment) that's in CD format at 44.1.
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Old December 18th, 2007, 09:21 AM   #4
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Problem solved:

I compressed the CD tracks with a compression factor of 99.66% and everything is now in sync.
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