[
http://dev.sourcefabric.org/browse/LS-258?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Romain Beauxis updated LS-258:
------------------------------
Reporter: anonymous
Priority: Minor (was: Blocker)
> Possible distortion issue...
> ----------------------------
>
> Key: LS-258
> URL: http://dev.sourcefabric.org/browse/LS-258
> Project: Liquidsoap
> Issue Type: Bug
> Components: Liquidsoap
> Reporter: anonymous
>
> Not sure entirely if this is a bug. Basically, as you might have saw on the
> mailing list, I had a issue with a small amount of noise being noticeable
> when the stream is supposed to be silent.
> I did a very hacked filter (which I know distorts audio to some degree
> because of the way it works) based on this...
> amplify(2.0, add([
> clip(min = 0.01, max = 1.0, stream),
> clip(max = -0.01, min = -1.0, stream) ]))
> Because I don't know how you can do a proper filter for white noise (i.e. one
> where you do a FFT to get the freq-amplitude domain, trim off anything that
> is below a the threshold where the noise stops, then do an inverse FFT to get
> back to the amp-time domain) I took this approach which I know will leave
> noise on when there is speech (it's not noticeable then), and I know it clips
> a bit of the singal as it tends towards 0 amplitude.
> Besides the fact the above code is a dirty ugly hack which probably will find
> it's way on the "Daily WTF", the below code in theory shouldn't alter the
> audio noticeably (in an ideal world the result should be the same as the
> input, but obviously working in floats means there might be minimal change,
> though it shouldn't be an in any way noticeable).
> amplify(2.0, add([
> clip(min = 0.0, max = 1.0, stream),
> clip(max = -0.0, min = -1.0, stream) ]))
> In the above, nothing is discarded, the signal just gets split into two +'ive
> and -'ive sections. The add should join them together and the 2x amp should
> just reverse the cancelling (well merging with 0) from the add operation.
> However I found it often makes a noticeable degradation which makes things
> sound quite metallic.
> This isn't critical, as I should be doing my noise cancellation properly for
> a start, however basic filters shouldn't be distorting streams like this???
> I'm not using raw buffering so I can't think it's int over/under flows.
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