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48K camera audio, 96K external audio

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Garrett Robinson
48K camera audio, 96K external audio
on Mar 21, 2012 at 5:20:03 am

My friend just had his senior music school recital last night and asked me to video (which I happily did). I shot on a Canon 60D, which records audio in 48K, 16-bit. There was also an audio tech there recording the instruments. He recorded in Pro Tools at 96K, 24-bit.

Now, when I pull both audio files into my Pro Tools timeline, even when I line each song up at the beginning, they slide out of synch by the end. How do I fix this? I want to change my camera audio to 96K rather than change the external audio to 48K, but is this even possible? ANY tips or advice would be appreciated.


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Bouke Vahl
Re: 48K camera audio, 96K external audio
on Mar 21, 2012 at 8:36:23 am

There is no reason in the 48 vs 96 to get out of sync.
But really, why do you need 96Khz? Are you ears good enough to hear frequencies above 48K?
I'm a bit deaf at the moment, my hearing goes up to 8 Khz...
I admit, that's a bit low, but i doubt it very much you can find anyone amongst the seniors that can hear above 14Khz.

Besides, how exactly are you going to distribute your sound @ 96Khz?

Last but not least, scroll back a bit and you find a quazillion answers about proper sync....

Bouke

http://www.videotoolshed.com/
smart tools for video pros


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Andrew Rendell
Re: 48K camera audio, 96K external audio
on Mar 22, 2012 at 1:10:30 am

As I understand it the reason for using 96kHz sampling rate isn't about increasing the frequencies being reproduced, it's about reducing aliasing.

Weird things happen as the sound frequencies approach half the sampling frequency, which cause frequencies to be produced in the output that weren't there in the source (which is called aliasing). Look up modulation theory if you realy want to know why (think of the sampling frequency as a "carrier"), but the outcome is the unpleasant "metallic" harshness to the sound that you sometimes heard on early CDs, particularly on classical instruments like violins, pianos, etc, which produce harmonics going up to high frequencies. The solution to that is a very hard low-pass filter at 20kHz to get rid of any frequencies close to (or above) half the sampling rate (for 44.1 or 48kHz sampling), but that kind of filter causes phase distortion at high frequencies, so some degradation in absolute quality. Going up to 96kHz sampling simplifies the filtering requirements a lot as any degradation in quality will happen at frequencies well above human hearing, reproduction is better at the frequencies we want. (If you could invent the perfect low pass filter to block out everything above 20kHz without effecting frequencies below it you'd make the higher sampling rates pointless.)


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Richard Herd
Re: 48K camera audio, 96K external audio
on Mar 22, 2012 at 5:52:08 pm

http://people.xiph.org/~xiphmont/demo/neil-young.html


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Michael Gissing
Re: 48K camera audio, 96K external audio
on Mar 21, 2012 at 9:19:52 am

The timecode rates of both the ProTools session and the camera footage must match exactly.


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Garrett Robinson
Re: 48K camera audio, 96K external audio
on Mar 22, 2012 at 1:37:43 am

"quazillion answers" is kind of the problem. I found a ton of threads on synching but none with my exact problem.

I actually don't even mind if I have to convert the 96K to 48 at this point but how do I do this? I tried doing it with Soundtrack Pro but it didn't fix the synch issue. Someone else said to change the timecode signature - any advice how to do this? Probably my search-fu needs work but I couldn't find help on this subject either.

Thanks for any help, sorry for the noobish questions.


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Richard Herd
Re: 48K camera audio, 96K external audio
on Mar 22, 2012 at 5:53:46 pm

I use Compressor for that kind of thing. Have you used compressor before? It's a bit weird looking. Basically, you put your media file in there and then you apply presets and then you can change presets around for the exact settings you want.

In FCP, hit CMD-0 (that's a zero) and you can change the sequence settings.


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Andrew Rendell
Re: 48K camera audio, 96K external audio
on Mar 22, 2012 at 9:12:36 pm

If it's the timecode stamp, there's a tutorial about that here:
http://library.creativecow.net/lyon_matt/fixing-fcp-assets/1


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Garrett Robinson
Re: 48K camera audio, 96K external audio
on Mar 27, 2012 at 5:53:52 am

There! That tutorial! That was it. Handled. A thousand THANK YOUs!


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