Tips for USB Soundcards

My laptop speakers suck, so if a USB sound card is available, I'd rather use it. For this to work, I need the following to happen:

• When I plug in my USB sound card, it should become the default pcm and ctl.
• When I remove my USB sound card, the onboard sound card should be the default pcm and ctl.

The first step is to write a couple udev rules to execute a script. I'm not sure my rules are the best, but here they are:

      DRIVER=="snd-usb-audio", ACTION=="add", RUN+="/home/jesse/bin/select_alsa_default.sh"

      SUBSYSTEM=="sound", ACTION=="remove", RUN+="/home/jesse/bin/select_alsa_default.sh"

    

Next, I wrote the simple script. My idea was to use symlinks to choose between two different /etc/asound.conf files. Here's the script:

         #!/bin/bash

         rm /etc/asound.conf

         if [ "${ACTION}" == "add" ] 
         then 
           ln -s /etc/asound.conf.usb /etc/asound.conf
         else
           ln -s /etc/asound.conf.onboard /etc/asound.conf
         fi

      

Finally, create the two asound.conf files, asound.conf.onboard and asound.conf.usb. These two files are exactly the same, except for the following code at the bottom:

         pcm.!default {
                 type plug
                 slave.pcm "hda-intel"
         }

         ctl.!default {
                 type hw
                 card "0"
         }

      

One last thing: my USB sound card has no volume control, so I want to control the volume using the multimedia keys on the laptop. Normally, no problem: I've already set the default card control, so if I had bound the keys to change, say, PCM, then it would change the PCM of either the USB card or the onboard card, as desired. But my onboard card has two PCMs, so I prefer to change its Master setting, while my USB card has no Master control at all.

So, here's my solution. I set the keys as follows:

XF86AudioLowerVolume		amixer -c 1 set PCM 5%- || amixer -c 0 set Master 5%-
XF86AudioRaiseVolume		amixer -c 1 set PCM 5%+ || amixer -c 0 set Master 5%+
XF86AudioMute		amixer -c 1 set PCM toggle || amixer -c 0 set Master toggle

This way, the multimedia keys try to control card 1 (the USB card). If that fails (say, if the USB card is not present), then they will instead control card 0.

Because I use enlightenment, I used e16keyedit to make those changes. For other window managers, you'll have to use the appropriate tool.

Viola.