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Audio pitch correction 25fps to 24fps


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#1 Chris Mills

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Posted 06 July 2008 - 01:29 AM

I have a feature film produced and mastered as HD1080 25p which needs to be conformed to work at 24fps at an international film festival in Rhode Island later this year. We are having a little trouble locating resources to pitch correct the audio up 4% to compensate for the slower frame rate so that it does not seem to low.

Are there any tools that might be suggested to do this? I have the separate audio tracks which I can process and I own a copy of Cubase 4.1 so any VST plugins would be fair game. I am looking at some of Waves plugins, but I am concerned that these might choke on a long format audio file.

Are there any suggestions for accurate pitch correction that does not re-time the when it is played out at 24fps?

Thanks in advance.

Chris Mills, FX Supervisor/Shots TD (and now audio wrangler)
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#2 Brian Drysdale

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Posted 07 July 2008 - 06:14 AM

Quite a few film sound post production companies can do this.

I'd also check your sound track for long sustained musical notes, because the pitch changing process mightn't like them. I did one short film with pitch correction without a problem, on another the pitch correction didn't work with a woman singer on the music track, so we didn't bother doing it - also, if the 24fps pitch was played back at 25fps she sounded far too high (On the first film we had a 25fps master, then a separate master for Dolby optical sound with the pitch change).

The sound still has same running time as your pictures after pitch correction, you're not changing the speed of the sound track.
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#3 Thomas Worth

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Posted 14 July 2008 - 04:55 AM

What you're really doing is changing the duration of the soundtrack by 4%. This is really a time-stretch with pitch compensation, because playing the soundtrack back 4% slower will obviously lower the pitch. This means the duration of the film will be 4% longer after the frame rate conversion, so yes, you are most definitely re-timing the soundtrack.

The correct way to do this is to use separate time stretch algorithms for dialog, music and sound effects. Strings in the score will sound especially crappy if the wrong algorithm is used.

This is the best way to convert 25fps material to 24fps, so you're on the right track.
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#4 Chris Mills

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Posted 14 July 2008 - 05:07 AM

What you're really doing is changing the duration of the soundtrack by 4%. This is really a time-stretch with pitch compensation, because playing the soundtrack back 4% slower will obviously lower the pitch. This means the duration of the film will be 4% longer after the frame rate conversion, so yes, you are most definitely re-timing the soundtrack.

The correct way to do this is to use separate time stretch algorithms for dialog, music and sound effects. Strings in the score will sound especially crappy if the wrong algorithm is used.

This is the best way to convert 25fps material to 24fps, so you're on the right track.


Thanks! The audio house which was helping us originally was able to book time to take care of this in the manner to which you described. The re-timed HDCAM tape was transferred today and hopefully it will make it to the Rhode Island International Film Festival on time in a week or so.

Kind regards,
Chris Mills, FX Supervisor/Shots TD
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#5 Brian Drysdale

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Posted 18 July 2008 - 04:16 AM

What you're really doing is changing the duration of the soundtrack by 4%. This is really a time-stretch with pitch compensation, because playing the soundtrack back 4% slower will obviously lower the pitch. This means the duration of the film will be 4% longer after the frame rate conversion, so yes, you are most definitely re-timing the soundtrack.


The pitch correction itself doesn't change the running time, it's the changing of the frame rate that does this.
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#6 Thomas Worth

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Posted 19 July 2008 - 05:37 AM

The pitch correction itself doesn't change the running time, it's the changing of the frame rate that does this.

Right, it's the frame rate change that necessitates the re-timing of the sound, which necessitates the pitch correction.

Many times, this technique is used on foreign release DVDs but they leave out the last (pitch correction) step. The result is chipmunk voices!
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