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uaudio.4 revision 1.17 
 $NetBSD: uaudio.4,v 1.17 2004/10/03 10:50:20 wiz Exp $

 Copyright (c) 1999 The NetBSD Foundation, Inc.
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 This code is derived from software contributed to The NetBSD Foundation
 by Lennart Augustsson.

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.Dd October 4, 2004
.Dt UAUDIO 4
.Os
.Sh NAME
.Nm uaudio
.Nd USB audio device driver
.Sh SYNOPSIS
.Cd "uaudio* at uhub?"
.Cd "audio* at uaudio?"
.Sh DESCRIPTION
The
.Nm
driver provides support for
.Tn USB
audio class devices.

p
A
.Tn 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
.Nm
driver and are accessible via the mixer (see
.Xr audio 4 )
interface:
l -tag -width Dv -offset 3n -compact t 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
.Ar mixN-S ,
where
.Ar N
is a number that identifies which mixer it is and
.Ar S
which input.
t selector A selector unit select one of multiple audio sources such as mic-in
and line-in.
The name of the control is
.Ar feaN-S1S2S3... ,
where
.Ar N
is a number that identifies which selector unit it is and the sequence of
.Ar Sn
indicates candidate units for the audio source.
t feature A feature unit changes the sound in some way, like bass, treble, or
volume.
The name of the control is
.Ar feaN-S-F ,
where
.Ar N
is a number that identifies which feature unit it is,
.Ar S
which input, and
.Ar F
which feature is affected.
t 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
.Ar proN.M-enable ,
where
.Ar N
is a number that identifies which processing unit it is and
.Ar M
which kind.
Depending on the type of processing unit there may be other controls
as well.
t extension An extension unit performs some unspecified audio processing
The name of the on-off control is
.Ar extN-enable ,
where
.Ar N
is a number that identifies which processing unit it is.
.El

p
For more information the
.Tn USB
Audio class specification is indispensable
reading.
.Sh SEE ALSO
The
.Tn USB
specifications can be found at:
.Dv http://www.usb.org/developers/docs.html

p
.Xr audio 4 ,
.Xr usb 4
.Sh HISTORY
The
.Nm
driver
appeared in
.Nx 1.5 .
.Sh BUGS
There is no support for multiple-endpoints audio stream,
adaptive recording, async playback, and TYPE-II/III formats.

p
The mixer interface is really incomplete.
There should be some heuristics that allow important controls,
e.g., volume, to be identified and given their traditional name.