.TH AUDIO 3 
.SH NAME
audio \- SoundBlaster or ESS1688 audio controller
.SH SYNOPSIS
.nf
.B bind -a #A /dev
.sp 0.3v
.B /dev/audio
.B /dev/volume
.fi
.SH DESCRIPTION
The audio device serves a one-level directory,
giving access to the stereo audio ports.
.B Audio
is the data file, which can be read or written to use the port.
Audio data is a sequence of stereo samples, left sample first.
Each sample is a 16 bit little-endian two's complement integer;
the default sampling rate is 44.1 kHz.
Some implementations only support audio output
and return a zero length when read.
.PP
The length of the
.B audio
file as returned by
.IR stat (2)
represents the number of bytes buffered for input or output.
This provides some control over record or playback latency.
.PP
The file
.B audiostat
provides additional timing and latency control.  When read, it returns
lines of the form
.IP
.B "bufsize \f2s\fP buffered \f2b\fP offset \f2o\fP time \f2t\fP
.PP
reporting number of bytes
.I s
used for DMA operations (i.e., the minimum useful size for reads and writes),
the number of bytes
.I b
currently buffered, and the time
.I t
at which offset
.I o
was reached.  Using
.I t
and
.IR o ,
it is possible to calculate at what time a byte with a different offset will
be recorded or played back.
.PP
.B Volume
is the control file associated with the audio port.
Each input and output source has an associated stereo volume control,
ranging from 0 (quiet) to 100 (loud).
In addition, there are controls for the sampling rate of the D/A and A/D converters
and for any tone controls.
Reads
return lines of the form
.IP
.I source
.B in left
.I value 
.B right
.I value
.B out left
.I value
.B right
.I value
.PP
possibly abbreviated if the values are shared or non-existent.
For example, if all of the values are shared, the form degenerates to
.RI ` source
.IR value '.
Valid sources depend on the particular audio device,
though all devices have an
.B audio
stereo source, which controls the output volume from the D/A converter
connected to
.BR audio .
.PP
Writes accept the same format with same abbreviations.
Writing the string
.B reset
sets all of the attributes to their default value,
and if no attribute is supplied,
.B audio
is assumed.
.PP
The Sound Blaster 16 (or MCD) is half-duplex and accepts the following controls on its
.B volume
file,
in the format shown above for reads.
.TF "\fLspeaker in out"
.TP
.B audio out
Data written to audio.
.TP
.B synth in out
MIDI synthesizer.
.TP
.B cd in out
CD player.
.TP
.B line in out
Line-level input.
.TP
.B mic in out
Monaural microphone input.
.TP
.B speaker in out
Monaural internal speaker connection.
.TP
.B treb out
Stereo treble tone control.
Values less than 50 decrease the treble,
those greater increase it.
.TP
.B bass out
Stereo bass tone control.
.TP
.B speed in out
Sampling rate for the D/A and A/D converters,
expressed in Hz.
Defaults to 44100.
.SH SOURCE
.B /sys/src/9/port/devaudio.c
.SH SEE ALSO
.IR usb (4)