[pulseaudio-discuss] Bad Crackling with PA 0.9.12

[Colin Guthrie]

Sean McNamara wrote:
> I'm still getting this with the latest development snapshots of
> alsa-driver, alsa-lib, alsa-plugins and pulseaudio. Can't seem to
> figure it out except that I think the mixing math has been changed to
> "add" the amplitudes of the two sounds even if they ultimately end up
> overdriving.
> 
> Here's a very simple contrived test:
> 
> 1. Run `gst-launch-0.10 audiotestsrc wave=sine ! audioconvert ! volume
> volume=0.2 ! pulsesink &` several times (2 or 3 of them stacked).
> Notice, no distortion.

Indeed.

> 2. Kill all of those, and run `gst-launch-0.10 audiotestsrc wave=sine
> ! audioconvert ! pulsesink &` (volume element removed) twice. BZZZT!
> May want to remove headphones from ears for this one - painful.

I ran this and it got quieter... made me think that the waves were 
cancelling each other out... so killed and reran one of them... got even 
quieter... repeat.. pretty loud and nasty!

> 3. Kill pulseaudio and other audio-using apps, then run
> `gst-launch-0.10 audiotestsrc wave=sine ! audioconvert ! alsasink
> device=plug:dmix:0 &` twice. No bzzt! You have to run it *three* times
> with the volume at 0dB to get it to overdrive, probably because dmix
> uses saturation.

Yeah this seems more reliable for me too.... damn these noises are annoying!

> However, I have a very interesting result from a test of using the
> `float32ne` default sample format of the server: only the BZZZT!! of
> gst-launch is now observable using this sample format. Ordinary sounds
> (like the Rhythmbox-Pidgin case described above) work just fine.
> 
> So what's going on? It seems like using signed 16-bit samples for the
> mixing is causing the overdriving/crackling. 32-bit float samples,
> while more CPU-intensive, jive much better.

With your gst tests 32ne also are more ear friendly for me.


I have no idea what any of this means, but just trying your tests in 
case it helps!

Using hda-intel here and PA 0.9.12

Col


-- 

Colin Guthrie
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http://colin.guthr.ie/

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