====== ALSA ======

Disable specific sound cards (i.e. ATI HDMI when not in use):

This command shows all physical cards ALSA identified:
<code>cat /proc/asound/cards</code>

This command provides more details:
<code>aplay -l</code>

Identify the relevant kernel module using
<code>
lsmod | grep snd
</code>

Check for options of the module, e.g. snd_hda_intel
<code>
modinfo snd_hda_intel | grep enable:
# parm:           enable:Enable Intel HD audio interface. (array of bool)
</code>

Notice the 'array of bool' for this parameter.

To disable parts of this module, create a modprobe conf file and add options. The enable parameter requires values for each of the devices it found. e.g.
<code>
vi /etc/modprobe.d/snd-hda-intel.conf
</code>
note the module filename uses dashes instead of underscores
<code>
options snd-hda-intel enable=1,0,0
</code>

The enable parameter is an array of booleans that can enable/disable each card driven by the snd_hda_intel module. Look for "HDA-Intel" in "cat /proc/asound/cards" e.g.:
<code>
 0 [U0x46d0x8c9    ]: USB-Audio - [...]
                      [...]
 1 [PCH            ]: HDA-Intel - [...]
                      [...]
 2 [HDMI           ]: HDA-Intel - [...]
                      [...]
 3 [HDMI_1         ]: HDA-Intel - [...]
                      [...]
</code>

The three cards listed that are driven by "HDA-Intel" are PCH, HDMI, and HDMI_1 so to disable both HDMI cards, the enable parameter is "1,0,0".