Possible distortion issue...

[MiiJaySung]

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.

[smimram]

A proper way of removing the noise when there is no sound would be to use the strip_blank operator and do something like

mksafe(strip_blank(length=0.1, stream))

You should also adjust the threshold parameter of strip_blank if the noise is noisier than -40dB.

Filtering blank noise is usually quite hard because it is not confined to a particular frequency range, so I'm not sure that FFT would help so much here without degrading the signal.

I cannot hear the degradation in your example above, are you sure that it does not come from somewhere else in your script? Notice that you don't need the amplify with

add(normalize=false, [clip(min = 0.0, max = 1.0, stream), clip(max = -0.0, min = -1.0, stream)])

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