audio man page on Plan9

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AUDIO(3)							      AUDIO(3)

       audio - SoundBlaster or ESS1688 audio controller

       bind -a #A /dev

       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
       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 out‐
       put volume 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.



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