Tracking the sound problem.

Nigel Henry cave.dnb2m97pp at
Sun Feb 10 16:16:09 UTC 2008

On Sunday 10 February 2008 06:58, Tim wrote:
> On Sat, 2008-02-09 at 18:18 -0500, Tom Horsley wrote:
> > Why any sane kernel startup sequence would initialize any
> > removable devices before any fixed devices is a separate
> > question :-).
> I can imagine one reason:  The thought that an "added on" device might
> be to replace a built-in device that you can't remove.
> However, if I'm asked to configure what is my default sound card (as
> during the first-boot sequence), I expect that default to stay no matter
> what else is added.

Hi Tim. The way I've always understood this, regarding USB devices that use 
snd-usb-audio, is that because the USB comes up early in the boot process, 
anything that resembles an audio device (like my usb midi keyboard), gets set 
as card0. If your actual soundcard is aliased as card0, with the options line 
showing "index=0", it is unlikely to show up in /proc/asound/cards, as 
snd-usb-audio has already grabbed card0. Saying that though, you will 
probably still see that the modules have been loaded for your actual 
soundcard in /sbin/lsmod | grep snd, but because the soundcard isn't 
in /proc/asound/cards, it won't work.

The fix I've had to use since FC1, and on other distro's too, is to set alias, 
and options lines in /etc/modprobe.conf for snd-usb-audio, as below.

alias eth0 8139too
alias scsi_hostadapter libata
alias scsi_hostadapter1 pata_via
alias snd-card-0 snd-emu10k1
options snd-card-0 index=0
options snd-emu10k1 index=0

alias snd-card-1 snd-usb-audio
options snd-usb-audio index=1

options snd-bt87x index=2

options bttv automute=0
options tuner port2=0 pal=I

install pcspkr /bin/true

The module snd-bt87x above, is another notorious one, along with some modem 
modules, that like to grab card0, before anything else can. It's the sound 
capture module for my TV card, and some distro's have default options lines 
for these problematic modules, and set them as "index=2", thus stopping them 
grabbing card0.

If you have more than one audio device on the USB, it get's a little more 
complex, and you have to specify them by their PID's (product id's), and 
VID's (vendor id's). So for example you could have your webcam, and usb midi 
keyboard always taking the same position. I'll have to look for the exact 
details on this, as they were on the alsa-user list.

Just some Sunday afternoon (Northern France) passing the time stuff.


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