pulseaudio: no sound, Fedora 12, what debugging/diagnostic info is needed to solve this problem?

[Marko Vojinovic]

On Thursday 04 March 2010 04:32:35 am Rick Sewill wrote:
> I believe many software programs use alsa.
> I believe alsa, in turn, uses pulseaudio.

No. Userland apps talk to pulseaudio, which talks to alsa which talks to 
hardware. That is a natural flow of audio data (when doing playback). 
Pulseaudio is built and works on top of alsa.
 
> I must add a caveat.  I believe programs can be configured to use alsa.

If a program is configured to use alsa, the alsa-pulseaudio plugin would catch 
it trying to talk to alsa and redirect the communication to pulseaudio, which 
would mimic alsa for that app. After pulseaudio does its processing, it 
forwards the results to alsa. Only pulseaudio actually talks to the real alsa.

Of course, you can disable the plugin or pulseaudio and let apps talk directly 
to alsa, but that would be a broken configuration.

> I believe some programs can be configured to use pulseaudio, bypassing
> alsa.  I believe some programs can be configured to bypass pulseaudio,
> and go straight to the hardware device drivers.

All programs should be configured to use pulseaudio, if they support it. If 
not, they should be configured to use alsa, whereby the alsa-pulseaudio-plugin 
will interfere as above. Hardware device drivers are part of alsa, and no user 
app should ever talk to hardware directly.
 
> pavucontrol

Also, there are two mixers in the story --- the hardware mixer (for alsa) and 
the userland mixer (pavucontrol, for pulseaudio). In regular circumstances you 
never want to mess with the hardware mixer, since it is used by pulseaudio 
when communicating to alsa. The hardware mixer is not easy to access either, 
you must specifically ask for it to be displayed, using appropriate switches 
in, say, "alsamixer" app.

The only mixer that a user should actually use is pavucontrol. Or kmix or 
gnome volume control mixer or some other similar thing. They all handle 
basically the same controls (using different GUIs) and use pulseaudio in the 
background.

I hope this clears things up a little.

HTH, :-)
Marko