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No lossy codec is perfectly gapless, Here is the killer sample
post Feb 1 2004, 20:42
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I found a problem sample for gapless encoding. Whatever I do, there is an audible click between the tracks. I've analyzed its cause, and found that it comes from edge effects. The termination of the waveform far from zero causes ringing, that manifests itself as an audible click, even when the files are played gapless.

I saw the problem with MP3 and MusePack.

MP3 : Lame 3.90.3 --alt-preset standard ; Foobar2000 disc writer
MPC : Mppenc 1.14 --xlevel ; Mppdec

You can get the file here : http://www.hydrogenaudio.org/forums/index....35&t=18207&st=0

Look at the attached picture to see the problem in the waveform.
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post Feb 2 2004, 04:45
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Added the following files to the uploads

silent1.wav - 2 secs at 0dB
silent2.wav - 3 secs at 0dB

prepared by cutting a single 5sec .wav


steps.wav - 2 secs of digital silence, 2 secs at 0dB, 2 secs digital silence, 3 secs at 0dB, 1 sec of digital silence.

You should hear clicks at 2,4,6 and 9 secs.

I've found that this sort of click is associated with abrupt changes in level. It is, for example, the reason square waves sound harsh. It is not restricted to square edges by any means and the same effect can be heard at the end of a sine wave. If the last sample is at a peak the click is very sharp, but even if it terminates at a zero crossing there is still a definite 'wump', This is usually dealt with by adding a small amount of fade.

An mp3 adds digital silence and few bad samples at the begining and end of of a file, and if the threshold for silence detection is set too low then there will be a few bad samples that will cause a click at the join. I don't have foobar installed, but have been able to play gapless in Winamp with a little tweaking. Does foobar use the same technique ?

It seems to me there will always be an artefact (whether audible or not) using any technique that involves stripping silence and butting together mp3s. A look at the delta file shows that there is a cluster of inaccurate samples either side of the terminal points, so even if the silence is stripped from start and end there still exists a cluster of bad samples at the join.

(edit) Added waveform of stripped and butted silent1 and silent2 mp3 files to uploads. This is essentially equivalent to the delta file in this case (/edit)


This post has been edited by hujay: Feb 2 2004, 05:41
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