uaudio —
USB audio device driver
uaudio* at uhub?
audio* at audiobus?
The uaudio driver provides support for USB audio class
  devices.
A USB audio device consists of a number of components: input
    terminals (e.g. USB digital input), output terminals (e.g. speakers), and a
    number of units in between (e.g. volume control). The following types of
    units are handled by the uaudio driver and are
    accessible via the mixer (see
    audio(4)) interface:
  - mixer
- A mixer has a number of inputs and one output. Each input has a control
      that determines its volume in the output. The name of the control is
      mixN-S, where N is a number
      that identifies which mixer it is and S which
    input.
- selector
- A selector unit selects one of multiple audio sources such as mic-in and
      line-in. The name of the control is selN-S1S2S3...,
      where N is a number that identifies which selector
      unit it is and the sequence of Sn indicates
      candidate units for the audio source.
- feature
- A feature unit changes the sound in some way, like bass, treble, mute, or
      volume. The name of the control is determined in a heuristic way. If the
      unit changes the sound to a speaker output terminal, the names of the
      controls may be outputs.speaker.bass, outputs.speaker.treble,
      outputs.speaker.mute, outputs.speaker, or likewise.
- processing
- A processing unit does one of a number of audio processing functions
      (e.g., channel up-down mixing, Dolby ProLogic, or chorus effects). The
      name of the on-off control is proN.M-enable, where
      N is a number that identifies which processing unit
      it is and M which kind. Depending on the type of
      processing unit there may be other controls as well.
- extension
- An extension unit performs some unspecified audio processing The name of
      the on-off control is extN-enable, where
      N is a number that identifies which processing unit
      it is.
 
For more information the USB Audio class specification is
    indispensable reading.
The uaudio driver appeared in NetBSD
  1.5.
Releases 1.0 and 2.0 of the USB Audio class specification are not mutually
  compatible. The uaudio driver only supports devices
  compliant with Release 1.0.
There is no support for multiple-endpoints audio stream, adaptive
    recording, async playback, and TYPE-II/III formats.
There is the possibility that a device has multiple mixer items
    which have the same name.