I encountered an audio bug and reported it on Launchpad. There I was asked to reinstall PulseAudio.
That sounded dangerous, so I tried it on a VirtualBox virtual machine I had lying around. (this VM had no sound problems at all). And indeed, after I did a naive
sudo apt-get remove pulseaudio -> reboot ->
sudo apt-get install pulseaudio, the VM has no sound any more.
Strangely, everything looks OK. There is nothing muted (I unmuted every single playback chanel in alsamixer just in case). The driver for the sound card is recognized and loaded, aplay plays sound files without producing an error, and when I installed and opened PulseAudio Volume Meter, playing a sound resulted in the volume indicator changing with the sound. Only there is nothing coming out of the loudspeakers. This isn't a hardware problem either, because the sound in the host system is functioning.
I tried to configure PulseAudio as described on this page of the Ubuntu wiki, but had no success.
I am afraid to try the reinstall on my real system until I know how to do it without causing a problem. Did I miss a configuration step somewhere? Should I have reinstalled in some other way?
Both guest and host systems are Ubuntu 10.10 64 bit.