ALSA device labels
From the ALSA wiki
When you issue commands such as aplay or arecord, the commands may need to be told which ALSA devices you want them to use.
- If your sound card has two devices to play back sound (say, one analog for your PC speakers, and another digital, using an S/PDIF connection to your stereo), aplay will probably default to using the analog device. If you want it to use the digital device, you'll need to tell it to do so.
An ALSA device label generally looks something like hw:0,0 for the first hardware PCM device, default:0 for the device configured as the default (which in a vanilla 1.0.11 configuration is a Dmix'ed version of hw:0,0, etc.).
Unfortunately, at the current time (2006-06), there is no way to get ALSA to enumerate all the devices it knows about. This is regarded as a problem, and hopefully will someday be fixed. You can read more about this topic at FAQ001, proc asound documentation, and FAQ053.