[pulseaudio-discuss] Bad Crackling with PA 0.9.12

Sean McNamara smcnam at gmail.com
Fri Sep 12 11:12:30 PDT 2008


I'm running Mandriva 2009.0 RC1 with PA 0.9.12 (from the tarball) that
I compiled myself. Right now my worst problem with 0.9.12 is severe
(loud!) crackling whenever multiple streams are active at once.

I am using alsa kernel and lib 1.0.18rc3; previously I tried ALSA
1.0.17 with the same exact results. You might also be pleased to know
that I am stubbornly using one of those pesky and oft-broken
snd-hda-intel cards! :)

Here's a simple way to reproduce the issue:

$ for (( i = 0; i < 2; i++ )); do
#Pick a wav file that exists on your system
paplay /usr/share/sounds/shutdown.wav &

In 0.9.10 and prior, this would play the same sound file twice on top
of itself in very rapid succession, which would make it sound pretty
loud, but there wouldn't be horrible crackling. With 0.9.12, it sounds
like the loudness of each sound is combined, creating an amplification
that is _way_ overdriven, and hence the distortion. This occurs much
more noticeably in wav files that are normalized to 0dB, meaning that
the loudest parts of the file are set at 0dB. For very quiet sounds
whose internal structure consistently maintains a relatively low
volume, this effect is almost invisible.

Being normalized to 0dB has never been a condition causing this to
occur before; previous versions of pulse could play the same wave
files just fine without overdriving. Have the maths for
resampling/mixing changed now? And is this intended or accidental?

My config files are pasted: http://rafb.net/p/jW16b668.html and



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