SGI audio observations
Audio interface for the high-quality digital audio subsystems on IRIS
4D/30, 4D/35, and Indigo systems, and future IRIS audio subsystems.
Note that the obsolete IRIS 4D/20 has a different (/dev/audio) interface.
The device can only switch input ports, not output ports.
DC offset can be significant (1300 or more).
Recording/playback gain: 0..255