[pulseaudio-discuss] Bad Crackling with PA 0.9.12

Colin Guthrie gmane at colin.guthr.ie
Fri Sep 12 11:52:00 PDT 2008

Sean McNamara wrote:
> 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.

For your convenience and ease of testing there is an RPM for 0.9.12 in 
the cooker main/testing repo (has been there for yonks!)

> 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 &
> done
> 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
> http://rafb.net/p/cUUFj679.html

I'm also seeing some degree of crackling too, but not specifically when 
playing multiple streams.

To be honest, I think 0.9.12 is actually slightly worse than the last 
snapshot I built, but I can put my finger on it. The only change I can 
think of of late is one relating to a 
snd_pcm_hw_params_set_periods_near() call, but I've not looked hard at 
the code/changelog to see if there is some other thing that could be 
causing it.

That said, I've been getting this slight crackling ever since 0.9.11 but 
I've not had time to fully discuss this with Lennart yet... (always 
seems to be something more important to discuss!)

Oh and I'm also on hda! ;)



Colin Guthrie

Day Job:
   Tribalogic Limited [http://www.tribalogic.net/]
Open Source:
   Mandriva Linux Contributor [http://www.mandriva.com/]
   PulseAudio Hacker [http://www.pulseaudio.org/]
   Trac Hacker [http://trac.edgewall.org/]

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