AUDIO(3) AUDIO(3)
NAME
audio - SoundBlaster or ESS1688 audio controller
SYNOPSIS
bind -a #A /dev
/dev/audio
/dev/volume
DESCRIPTION
The audio device serves a one-level directory, giving access
to the stereo audio ports. 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.
The length of the audio file as returned by stat(2) repre-
sents the number of bytes buffered for input or output.
This provides some control over record or playback latency.
The file audiostat provides additional timing and latency
control. When read, it returns lines of the form
bufsize s buffered b offset o time t
reporting number of bytes s used for DMA operations (i.e.,
the minimum useful size for reads and writes), the number of
bytes b currently buffered, and the time t at which offset o
was reached. Using t and o, it is possible to calculate at
what time a byte with a different offset will be recorded or
played back.
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
source in left value right value out left value right
value
possibly abbreviated if the values are shared or non-
existent. For example, if all of the values are shared, the
form degenerates to `source value'. Valid sources depend on
the particular audio device, though all devices have an
audio stereo source, which controls the output volume from
the D/A converter connected to audio.
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AUDIO(3) AUDIO(3)
Writes accept the same format with same abbreviations.
Writing the string reset sets all of the attributes to their
default value, and if no attribute is supplied, audio is
assumed.
The Sound Blaster 16 (or MCD) is half-duplex and accepts the
following controls on its volume file, in the format shown
above for reads.
audio out Data written to audio.
synth in out MIDI synthesizer.
cd in out CD player.
line in out Line-level input.
mic in out Monaural microphone input.
speaker in out Monaural internal speaker connection.
treb out Stereo treble tone control. Values less
than 50 decrease the treble, those greater
increase it.
bass out Stereo bass tone control.
speed in out Sampling rate for the D/A and A/D convert-
ers, expressed in Hz. Defaults to 44100.
SOURCE
/sys/src/9/port/devaudio.c
SEE ALSO
usb(4)
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