Alsa - how can I tell my default audio output is card 2 and device 0, not hdmi?

Question

How can I tell my system default sound output is card 2 and device 0, and not card 2 device 3 or 7 or 1?

I did this, but no sound.

$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Device [C-Media USB Audio Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: PCH [HDA Intel PCH], device 0: ALC892 Analog [ALC892 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: PCH [HDA Intel PCH], device 1: ALC892 Digital [ALC892 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: PCH [HDA Intel PCH], device 7: HDMI 1 [HDMI 1]
  Subdevices: 0/1
  Subdevice #0: subdevice #0

$ cat /etc/asound.conf
#pcm.!default { 
#  type plug; 
#  slave { pcm "hw:2" } 
#} 
pcm.!default {
    type hw
    card 2
    device 0
}

Answer 1

If you find that your sound cards keep switching indices, you won't be able to hardcode defaults.pcm.card 2 in /etc/asound.conf. One (complex) approach might work, is to configure the sound kernel modules with your desired priority.

This approach is described in Debian Bug #614113:

1. run alsamixer;
2. use F6 and research available sound devices
3. set correct levels for playing on devices;
4. run some sound player that allow select sound devices (audacious for example);
5. play with you sound devices (with repeating steps 2,3) and decide what should be default;
6. exit alsamixer and player;
7. login as root;
8. run lsmod | grep snd and try to understood what modules corresponds to physical sound devices;
9. if unsure that you correctly determine modules on step 2: go to /sys/module and inspect all directories wich names begins with "snd". This directories names exactly as modules. If you will see "drivers" directory in inspected directory - then name of inspected directory is name of module that corresponds to physical sound device. Remember (wrote in notepad) all such modules.
10. run modinfo <module name> | grep desc for each module that yo found at steps 2 and 3. Read descriptions and make decidion about priorities of this modules. This will be priorities of corresponding sound devices.
11. go to /etc/modprobe.d;
12. create snd_cards_priorities.conf;

13. write to snd_cards_priorities.conf something like this:

    alias snd-card-0 <module for highest priority card>
    options <module for highest priority card> index=0
    alias snd-card-1 <module for lower priority card>
    options <module for lower priority card> index=1
    

14. save file;
15. restart alsa with /usr/sbin/alsa force-reload command;
16. run cat /proc/asound/cards command and check that sound devices are in correct order (device #0 has highest priority);
17. repeat steps 9, 10 several times and check that sound devices order is not changing;

18. exit root;

19. run alsamixer and configure you default sound device, exit alsamixer.

20. use you favorite sound player to test you new configuration.

Answer 2

To set the default device, you should not redefine the default device but simply put the following into /etc/asound.conf:

defaults.pcm.card 2      # or better "PCH"
defaults.pcm.device 0

This will work only for programs that actually use a default device without explicitly specifying a device. If some program like PulseAudio or VLC has been configured for some specific output device, you must change that configuration.