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Thread: Audio slipping

  1. #1
    Newbie Member johnnylandrover's Avatar
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    Audio slipping

    First project with 4.6 and my audio is slipping 3-5 frames. Capturing 1 to 1 rtv file with wav audio @ 32K stereo.

    Johnny

  2. #2
    Registered User ted's Avatar
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    John, I might suggest 48k.
    I dropped a 44k file on the timeline and I got intermittent slipping of the audio and video. I never researched it, but I've always had our audioman give me 48k since and haven't seen it since.
    It might have been another issue with the file, but it's a start.
    Who knows what Vodoo different programs do to files. Our Audioman uses Saw Pro for what it's worth.
    Ted R. Ruiz Sr.
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  3. #3
    Quote Originally Posted by johnnylandrover
    First project with 4.6 and my audio is slipping 3-5 frames. Capturing 1 to 1 rtv file with wav audio @ 32K stereo.

    Johnny
    Why do you capure in 32k stereo when you are capturing uncompressed video? Try 44.1 or 48k stereo... that might help...

    Or can someone else confirm this problem aswell?

    thanks
    chribba

  4. #4
    Newbie Member johnnylandrover's Avatar
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    chribba,
    Only capture that way because it loads into tmpeg without a problem. 48K is a problem for me.

    Johnny

  5. #5
    Thats very odd, i have not had that problem with tmpeg and has never capture lower than 44.1....

    chribba

  6. #6
    XDCAM HD production ScorpioProd's Avatar
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    48k is what you want.

    If you are making DVDs, they must be 48k, so I'm not sure what you're doing in TMPGEnc.

    More importantly, you really don't need to process the audio in TMPGEnc anyway.
    Eugene
    Scorpio Productions

  7. #7
    Newbie Member johnnylandrover's Avatar
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    So what your all saying is 32K audio does not work well and why is it slipping?Is 48k the only way to go or are there other options?

    Johnny

  8. #8
    XDCAM HD production ScorpioProd's Avatar
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    Well, 48KHz is the standard audio sampling for DVDs, period. They must be that.

    48KHz is the normal two channel DV/DVCAM/DVCPRO25 sampling as well.

    So, with these standards all being the same, it is best to use them all around. The only exception is CD audio, which is 44.1KHz, and gets converted nicely in VT-Edit.

    Of course, if you are using your DV camcorder in the four channel/32KHz mode, that may be why you're chosing that sampling rate? That could also explain why there may be some issues with conversion, I guess...
    Eugene
    Scorpio Productions

  9. #9
    Newbie Member johnnylandrover's Avatar
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    Maybe I'm not on the same page as most of you but I'm working with Sony's Xdcam 50 mbs and 4 tracks of audio @ 32K. So can I work with 32K or it will slip.

    Johnny

  10. #10
    XDCAM HD production ScorpioProd's Avatar
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    OH, XDCAM with four channel audio...

    But from what you describe it sounds like you're going in analog, so the sampling rate that you originally captured at doesn't matter.

    Note that 4.6 supports MXF XDCAM files with the proper codec, so you don't have to go analog.
    Eugene
    Scorpio Productions

  11. #11
    Newbie Member johnnylandrover's Avatar
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    Thanks for the info, but why does 32K slip? does anyone know?

    Johnny

  12. #12
    I'm not sure, but just about all the editors have trouble with it. Everything from pops to playing back at 48Khz chipmunk speed.

    That is one of the first things we train customers to do, avoid 12 bit/32Khz audio at all costs. Unfortunately most cameras default to 12 bit even if they have no external mic input.
    John Perkins
    Software Engineer

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  13. #13
    Broadcast Engineer tonsofpcs's Avatar
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    The math:
    NTSC field Rate = 60*1000/1001
    Recipricol field rate = 1001/60*1000

    (32000*1001)/(60*1000) = 533.86666666666666666666666666667
    (44100*1001)/(60*1000) = 735.735
    (48000*1001)/(60*1000) = 800.8

    See the problem?
    tonsofpcs (Eric Adler)
    http://www.videoproductionsupport.com/

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