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Sync Sound Problem

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Zach Kuperstein
Sync Sound Problem
on Aug 12, 2009 at 4:21:30 pm

I've shot 720p/24pn footage on the Panasonic HVX and recorded audio with an external Tascam recording device at 16bit/48khz. I then try to sync the footage with the audio in FCP using a clapped slate and aside from the clap itself, they are not even close.

I've read forums saying that the sequence settings must match the audio bitrate and they do.

I should note that the audio is a .wav file if that makes a difference.

Any thoughts on why my sound won't sync up? Any suggestions on what I might try to fix it?


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Ty Ford
Re: Sync Sound Problem
on Aug 12, 2009 at 6:00:43 pm

Hello Zach and welcome to the Cow Audio Forum.

Bit rate data, e.g. 16-bit or 24-bit, has no bearing on sync. Closely matching sample rates, frame rate or digital sync via time code and word clock are what determines sync.

I'm thinking there's something about the 24pn that's the problem. Might be that your camera is at 23.976 and not 24. Make a copy of your files and experiment with sample rate conversion to see if that helps.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Zach Kuperstein
Re: Sync Sound Problem
on Aug 12, 2009 at 9:11:02 pm

Hi Ty!

Thank you for your prompt response!

When I said bitrate, I definitely realize now that I meant sample rate. The sample rates do indeed match from the recorded audio to the FCP sequence settings.

Also, I have never heard of a "word clock" and I'm curious as to how I go about comparing that measurement in one place to another.

Anyway, I tried several sample rate conversions (using quicktime and exporting as an AIFF) above and below the original sample rate to no avail.

As for the visual footage, it is indeed at 23.98fps, but so is the sequence. And I'm pretty sure I have the correct sequence settings for the visuals.

Just for kicks I also tried speeding up the footage a bit to %110 and that way it stays pretty much in sync, but I definitely see some frame blending and there must be a better way!

Any additional thoughts?


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Ty Ford
Re: Sync Sound Problem
on Aug 12, 2009 at 10:36:34 pm

figure the percentage drop from 24 to 23.976 and pitch the wild sound down by that much,
or as you almost did the other way, speed the pix up but at the specific %.

Let us know how that works.

Typically unless you are locked by a master source for word clock or smpte, any sync you get is pretty much accidental.

You may have to slice out parts of whatever turns out to be the slower source to keep sync.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Zach Kuperstein
Re: Sync Sound Problem
on Aug 13, 2009 at 3:09:45 pm

Very good info! Thanks for the help.

I was never actually able to sync it up properly, but by slowing down the audio by about 10% (with a little guess and check to make it perfect) I got it to work. Luckily I had only one (very long) clip to do this on and there was no dialogue.

All that said, I'm still not sure what the actual problem was and it definitely wasn't the frame rate because 24 to 23.98 is a difference of much less than 10%.

Thanks again,
Zach


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