Logic Pro changing audio automatically?

Discussion in 'Recording Studio' started by narad, Jul 10, 2019.

  1. narad

    narad SS.org Regular

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    So I've been trying to track down this anomaly and have it down to a pretty specific situation at this point. So if I take a procedurally generated piece of audio, like a square or sawtooth, and examine it with something like matplotlib, it looks predictably like this:

    [​IMG]

    But, if I take that wav file, import it into an empty Logic project, and immediately export or bounce, normalization off, back to wav, what seems to be the same sampling rate / bit rate:

    [​IMG]

    I find this super weird. While I can imagine some default audio processing going on, you wouldn't expect it to be so destructive! Note that even the amplitude of the signal has been significantly decreased. Of course, it sounds the same to my ears, but that's not really the point. Anyone know what's going on here?
     
  2. narad

    narad SS.org Regular

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    Actually I sort of take it back: the two files do sound a bit different to me when played back-to-back, accounting for amplitude differences. That's crazy...it's like actually changing the overtones in the file purely in reading it in and exporting it.
     
  3. DudeManBrother

    DudeManBrother Hey...how did everybody get in my room?

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    Are you bouncing at 44.1? If you worked at 192 and bounced at 192 does it still happen?
     
  4. narad

    narad SS.org Regular

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    the original file is 44.1 and the bounce is 44.1. I'm not sure if there's some internal project or track setting that may be off?
     
  5. Lorcan Ward

    Lorcan Ward 7slinger

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    Logic has a lot of internal settings, even some hardcoded stuff. A studio engineer explained it to me but it went a bit over my head at the time.
     
  6. DudeManBrother

    DudeManBrother Hey...how did everybody get in my room?

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    This is only a guess; but at a low sample rate the harmonic distortion starts to fall back and produce the unwanted sine wave. The only way to really verify this theory is to increase the sample rate and render at the same higher rate to see if the wave changes.
     
  7. narad

    narad SS.org Regular

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    Yea, doesn't seem to be it. I set the project audio settings to 96, then imported the song, and then bounced at 96. Still looks weird in matplotlib.
     

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