How do I select a default sound card with alsa?

Solution 1:

Find your desired card with:

cat /proc/asound/cards

and then create /etc/asound.conf with the following entries:

defaults.pcm.card 1
defaults.ctl.card 1

Replace 1 with number of your card determined above. Source: https://www.alsa-project.org/wiki/Setting_the_default_device

Solution 2:

This is a way set default sound output card dynamically using PulseAudio (not ALSA).

1. Check list of Sources and Sinks

   $ pactl list short sources
   0   alsa_output.pci-0000_00_1b.0.analog-stereo.monitor  module-alsa-card.c  s16le 2ch 44100Hz   SUSPENDED
   1   alsa_input.pci-0000_00_1b.0.analog-stereo   module-alsa-card.c  s16le 2ch 44100Hz   SUSPENDED
   2   combined.monitor    module-combine-sink.c   s16le 2ch 44100Hz   SUSPENDED
   
   $ pactl list short sinks
   0   alsa_output.pci-0000_00_1b.0.analog-stereo  module-alsa-card.c  s16le 2ch 44100Hz   RUNNING
   1   combined    module-combine-sink.c   s16le 2ch 44100Hz   IDLE
   2   alsa_output.pci-0000_01_00.1.hdmi-stereo    module-alsa-card.c  s16le 2ch 44100Hz   RUNNING
   

2. Set defaults:

   $ pactl set-default-source alsa_input.pci-0000_00_1b.0.analog-stereo
   $ pactl set-default-sink alsa_output.pci-0000_00_1b.0.analog-stereo
   

It is possible even to set ports too. See How to switch sound output with key shortcut

Reference: man pactl