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