term% cat index.txt AUDIO(3) Library Functions Manual 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 writ‐
ten 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) represents the num‐
ber 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 sam‐
pling 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 ex‐
ample, 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 vol‐
ume from the D/A converter connected to audio.
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 converters, expressed in Hz.
Defaults to 44100.
SOURCE
/sys/src/9/port/devaudio.c
SEE ALSO
usb(4)
AUDIO(3)