Distortion that sounds like clipping, but isn't

Discussion in 'Digital Audio' started by vashbul, Nov 9, 2016.

  1. vashbul macrumors newbie

    Joined:
    Aug 26, 2011
    #1
    I have been capturing audio from a site called "Name My Tune", where people sing or whistle a tune into their computer in hopes someone will identify it.

    There's an odd kind of distortion that shows up in a lot of the samples posted - a clicking noise that sounds like clipping distortion due to overmodulation, but if you look at the waveform on an editor like Audacity, you don't see the characteristic "broken" peaks. And it seems to happen whether the source is loud or soft.

    Here's what one sample looks like. Top: an 8 sec. clip. Bottom: close-up from the same sample
    [​IMG]

    Notice there seems to be some ultra-low frequency mixed into the signal. I can eliminate that for the most part by using a low-cut filter, but the "clipping" noise remains, which tells me it's not just a matter of my dinky computer speakers not being able to handle the subsonic signal.

    Here's the clip I'm talking about - hear the buzzing noise?


    So can anyone suggest how to fix this? Thanks, Peter.
     
  2. xb2003 macrumors 6502

    xb2003

    Joined:
    Jan 18, 2016
    Location:
    MO
    #2
    It's possible that when the files are uploaded, they are resampled from say 48kHz to 44.1kHz. That would be my guess.
     
  3. vashbul thread starter macrumors newbie

    Joined:
    Aug 26, 2011
    #3
  4. xb2003 macrumors 6502

    xb2003

    Joined:
    Jan 18, 2016
    Location:
    MO
    #4
    Resampling would occur when users upload their clips, you are downloading what's on the site.

    A good test would be to see if a different computer on a different network does the same thing for the same clips.
     
  5. vashbul thread starter macrumors newbie

    Joined:
    Aug 26, 2011
    #5
    Possibly resampling caused it - I'm more interested in how to fix or compensate for it than where it came from. Do you think if I re-resampled it myself, the damage would be undone, or is that a lost cause?
     
  6. vashbul thread starter macrumors newbie

    Joined:
    Aug 26, 2011
    #6
    Update: tried resampling, no effect.
    If I knew a name for this kind of artifact, maybe I could find a filter that was made to deal with it.
     
  7. cargoplex macrumors member

    cargoplex

    Joined:
    Mar 10, 2006
    Location:
    Bethesda, MD
    #7
    The other posters are correct that this is an artifact of poor quality resampling. The issue is baked into the file by the time you hear it on that site, so nothing you do can eliminate it after the fact. As xb2003 indicated, the files are most likely converted (resampled) upon upload. The real question is for the site owner, and those questions would be:

    1. Is there any post processing (resampling, encoding, etc.) done to my audio files after they are uploaded?

    2. What is the ideal format (wav, mp3, etc.) to use when uploading my audio?
     

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