Re: /dev/* and ALSA.

[Ralf Mardorf <ralf.mardorf@alice-dsl.net>]

On Mon, 2014-02-03 at 08:45 -0800, peter@easthope.ca wrote:
> Now I have /dev/USBspeakers and /dev/USBheadset, and wonder whether 
> ALSA can recognize /dev/USBspeakers rather than "SiS7012 AC'97 
> Sound Controller" as the default device.
> 
> http://wiki.debian.org/ALSA mentions "indexes" and /dev/dsp.
> No other /dev mentioned.  ALSA indexes predate udev; correct?
> 
> http://www.tldp.org/HOWTO/Alsa-sound-6.html mentions /dev/snd/*.
> No mention of making a specific /dev/snd/ the default.
> 
> Does anyone have a way of configuring a specific /dev as default?

This is how my Arch's alsa-base.conf looks like:

[rocketmouse@archlinux ~]$ cat /etc/modprobe.d/alsa-base.conf 
# ALSA module ordering
options snd slots=snd_hdspm,snd_ice1712,snd_ice1712

The HDSP is the default device hw:0, the both ICE1712 cards are hw:1 and
hw:2. If I unload the ICE1712 driver and connect USB audio devices those
device anyway will become hw:3, hw:4 etc..

A demonstration:

[rocketmouse@archlinux ~]$ hdspmixer
Card 0: RME AIO S/N 0x579bcc at 0xfddf0000, irq 18
Card 1: TerraTec EWX24/96 at 0xbf00, irq 20
Card 2: TerraTec EWX24/96 at 0xbb00, irq 21
Card 3: USB Device 0x170b:0x11 at usb-0000:00:13.0-2, full speed
Card 4: KORG INC. nanoKONTROL at usb-0000:00:13.3-1, full speed

[rocketmouse@archlinux ~]$ sudo modprobe -r snd_ice1712

[rocketmouse@archlinux ~]$ hdspmixer
Card 0: RME AIO S/N 0x579bcc at 0xfddf0000, irq 18
Card 3: USB Device 0x170b:0x11 at usb-0000:00:13.0-2, full speed
Card 4: KORG INC. nanoKONTROL at usb-0000:00:13.3-1, full speed

Even if I unplug and reconnect an USB device it never will become hw:1
or hw:2.

IOW you need to use

options snd slots=snd_usb_audio

to make an USB device always hw:0. Using this method hw:0 will be
reserved for USB audio, even if no USB audio is connected to the
machine. The index method is obsolet.