Latest post Wed, Apr 11 2018 2:18 PM by rpearlster. 6 replies.
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  • Tue, Apr 10 2018 8:07 PM

    • rpearlster
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    • Joined on Thu, Oct 8 2009
    • Posts 5
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    Audio loosing sync and drifting

    hi,

     

    A student of mine is trying to sync up her video from a project. Unfortunately they shot the video on the RED at 23.98 and recorded the audio at true 24. When they try to sync up it drifts out of sync. what do they have to do to make this work? Thanks, Rachel
  • Tue, Apr 10 2018 8:28 PM In reply to

    Re: Audio loosing sync and drifting

    Audio does not have a framerate (at best, its TC counter uses a framerate, but that has no influence on the actual speed), sound speed is determined by sample rate. If this happens, it looks like the cam ran at 24fps and that a 23.976fps slowdown was generated from that. If so, you'll need to restamp the audio's clock rate from 48000 to 47952 Hz before importing it into MC, so that it will be slowed down before import, to match the slowdown of the picture from 24 to 23.976.

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  • Tue, Apr 10 2018 8:36 PM In reply to

    • rpearlster
    • Not Ranked
    • Joined on Thu, Oct 8 2009
    • Posts 5
    • Points 45

    Re: Audio loosing sync and drifting

    thanks!

     

    The camera video is at 23.98 however it got there.  The audio is at true 24 or at a sample rate that doesn't match. I mispoke about it having a fps rate.

    In any case, what is the proceedure/program to do the pull down (is this the correct term?) from 48000 to 47952? 

     

    thanks!

  • Tue, Apr 10 2018 8:58 PM In reply to

    • rpearlster
    • Not Ranked
    • Joined on Thu, Oct 8 2009
    • Posts 5
    • Points 45

    Re: Audio loosing sync and drifting

    also,

     

    I'm tried altering the audio to 100.1% to see if that helps but it doesn't.  I'm really at a loss about how to proceed. 

     

     

     

  • Tue, Apr 10 2018 9:16 PM In reply to

    • rpearlster
    • Not Ranked
    • Joined on Thu, Oct 8 2009
    • Posts 5
    • Points 45

    Re: Audio loosing sync and drifting

    I've also tried rexporting the Wav with a new sample rate and that doesn't work either.

     

    Does anyone have an answer about what we need to do?

     

  • Wed, Apr 11 2018 6:17 AM In reply to

    Re: Audio loosing sync and drifting

    You should not sample rate convert the file, but rather change the clock rate as it is stamped in the file. You can do that using Wave Agent from Sound Devices (freeware).

     

    http://24p.com/wordpress/?p=195

     

    P.S. Changing the sound to 100.1% would’t work because you need to slow it down, not speed it up. Also, the difference is not 0.1% but 0.001%. So 0.999 to go from 24 to 23.976, and 1.001.001.001.001 to go from 23.976 to 24.

    Media Composer /w Symphony option | PT-HD | Win7Pro64 HP | OSX MBP | ISIS5000 | Nitris DX | Artist Mix & Transport & Color | AJA T-Tap | Decklink... [view my complete system specs]
  • Wed, Apr 11 2018 2:18 PM In reply to

    • rpearlster
    • Not Ranked
    • Joined on Thu, Oct 8 2009
    • Posts 5
    • Points 45

    Re: Audio loosing sync and drifting

    thanks!

     

    I have also tried resetting the sample rate to 47.952kHz in Wave Agent. Is this what you are referring to? It also didn't work. If "changing the clock rate as it is stamped in the file" is something different than that, where can I find the information about how to do that? Thanks.

     

    I also tried slowing it down .1% also.  I got the figure .1% from another person on the forum but yes, I see what you mean.  It's 1.001% to go from 23.976, correct ? At any rate, niether made a difference. 

     

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