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strange audio distortion, any ideas about what could cause it?
post Jul 10 2012, 09:34
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I'm guessing this is probably a hardware or system problem rather than an mp3 or an application software problem, but the symptoms are unlike anything I've encountered in the digital realm before. I have no idea of what kind of computer problem could produce this kind of distortion. I've put in a support request to the application software company but I have little hope they will find the source of the problem. Maybe someone has a useful idea.

A sample is attached as the last entry in
(this restriction for attachments that Hydrogen Audio has, unlike any other forum I've ever used, is rather a pain).

The process starts with a perceptually encoded audiobook file. One program plays it in real time. Another program inputs that playback and encodes it as mp3. The second program has installed a "virtual soundcard" that the first program uses for output; no audio hardware is involved.

There is no actual hardware soundcard on the computer (drivers for the MB soundchip have not been installed and said soundchip is turned off in the BIOS). The computer is not connected to any network. It has no wireless hardware. It is running no anti-virus or automatic updates. The OS is 64 bit Win7, so it does whatever Windows always does in the background, but nothing has been added to that.

This process worked without flaws for at least 20 audio books. The audio quality was always good. The distortion in this eight hour file started a little more than three hours into it. It is not continuous, there are some breaks back into normal, but most of it is distorted. The source file has no distortion.

I did not listen to more than about 15 minutes of distortion, so I don't know how far it extends, or if there is more of it later. I did sample a few snippets further on, here and there, without finding any problem, but this covered only a tiny part of the total audio. I also sampled a little bit of another audio book processed weeks later and found nothing wrong, but again the sampling is too limited to really know anything for sure except that the distortion is not continuous. (Both books are 30+ hours long, each.)
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post Jul 10 2012, 10:09
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Just a guess: it's possible this specific type of distortion is linked to the original file format - is the file/codec "audible", or some other speech-optimised codec?

If that's the case, the reason you haven't heard it before is because you've never heard the decoding of this type of file "go wrong" before - it's the sound of the codec trying to decode data that's been corrupted in some way.

Why the decoder is getting wrong data is another question - but if you can prove that this kind of distortion is caused by sending corrupt data to that codec, then you at least know at what part in the audio chain things are going wrong.

If corrupt data in this format doesn't cause those kinds of distortions, then it doesn't help at all. It could be something entirely different, like a buffering problem.


This post has been edited by 2Bdecided: Jul 10 2012, 10:10
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