Ok, just learned that having two sound cards in your system can lead to all kinds of trouble.
Some time ago I had bought some headphones from Altec Lansing that came with an USB adapter. Not expecting it to work in Linux I plugged it in, but lo and behold it actually worked and I had now two sound cards in my system according to Fedora's Soundcard Detection utility. So far so good.
Soon after I removed the USB module and just connected the headphones directly like I had always done and life was perfect.
Until quite some time later I had to reboot my machine and suddenly I was getting all these weird ALSA errors from all kinds of programs (see for example the image of the pop-up that appeared at KDE startup).
The strange thing was that the Soundcard Detection program reported everything okay, the right sound card was detected, I could hear the sample and on top of that several programs did actually produce sound. So what was going on here?
Finally today I got a hint trying to run alsamixer when it gave me the following error:
alsamixer: function snd_ctl_open failed for default: No such device
- ALSA user list which didn't really have a direct solution for my problem, but it made me look at the modules where I foundsnd-usb-audio. So what was that doing there when I had removed that USB adapter ages ago? Of course/etc/modprobe.conf was the "culprit" here. Somehow plugging in the USB adapter had inserted some lines into the file but removing the adapter hadn't deleted them!
- LinuxQuestions.org pointed me to some files I had never heard off: /etc/asound.state and /etc/asound.conf. The first didn't seem too interesting, but the second had things like card numbers which made me think that maybe they had gotten mixed up somehow because for a short time I had two sound cards in my system. So I removed both and restarted the Soundcard Detection program. And like I had imagined the numbers were different in the new asound.conf!
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