Ever since installing Karmic on my main box, audio has been an intermittent annoyance. While I like the idea behind pulseaudio, its presence in Karmic has certainly has contributed to a few headaches (made painfully worse when I imprudently tried exploring the network multicast features). I’ve had most of the bugs worked out for a while, except for one: before a sound is played back, a loud, unpleasant, sharp crack is emitted by the speakers. After that, sound playback proceeds normally…music, further OS alert beeps, no problem. However, after a period of idleness without any sound activity (ten seconds, in fact), the next speaker access will result in the same loud report. Even though annoying, this problem has not been critical.
The box is custom-built system based around an Asus P6T motherboard, which has has an onboard RealTek ALC1200 for sound. This shows up in Linux as
00:1b.0 Audio device: Intel Corporation 82801JI (ICH10 Family)
HD Audio Controller
and thus uses the snd_hda_intel kernel module (Intel High-Definition Audio).
Having just had occasion to look into my /etc/modprobe.d/alsa-base.conf, I found this exceedingly suspicious pair of lines:
# Power down HDA controllers after 10 idle seconds
options snd-hda-intel power_save=10 power_save_controller=N
The 10-second time-out surely could not be a coincidence.
Sure enough, commenting it out has removed this lingering audio annoyance (which turns out to be completely unrelated to pulse). It appears this issue is already known: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/417302. As one commenter observed: “I was also affected by this. I think this is a bug – speakers should not produce unpleasant sounds for [no] apparent reason.” This is a sentiment with which I can only agree.