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audio 2.9 KB

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  1. .TH AUDIO 3
  2. .SH NAME
  3. audio \- SoundBlaster or ESS1688 audio controller
  4. .SH SYNOPSIS
  5. .nf
  6. .B bind -a #A /dev
  7. .sp 0.3v
  8. .B /dev/audio
  9. .B /dev/volume
  10. .fi
  11. .SH DESCRIPTION
  12. The audio device serves a one-level directory,
  13. giving access to the stereo audio ports.
  14. .B Audio
  15. is the data file, which can be read or written to use the port.
  16. Audio data is a sequence of stereo samples, left sample first.
  17. Each sample is a 16 bit little-endian two's complement integer;
  18. the default sampling rate is 44.1 kHz.
  19. Some implementations only support audio output
  20. and return a zero length when read.
  21. .PP
  22. The length of the
  23. .B audio
  24. file as returned by
  25. .IR stat (2)
  26. represents the number of bytes buffered for input or output.
  27. This provides some control over record or playback latency.
  28. .PP
  29. The file
  30. .B audiostat
  31. provides additional timing and latency control. When read, it returns
  32. lines of the form
  33. .IP
  34. .B "bufsize \f2s\fP buffered \f2b\fP offset \f2o\fP time \f2t\fP
  35. .PP
  36. reporting number of bytes
  37. .I s
  38. used for DMA operations (i.e., the minimum useful size for reads and writes),
  39. the number of bytes
  40. .I b
  41. currently buffered, and the time
  42. .I t
  43. at which offset
  44. .I o
  45. was reached. Using
  46. .I t
  47. and
  48. .IR o ,
  49. it is possible to calculate at what time a byte with a different offset will
  50. be recorded or played back.
  51. .PP
  52. .B Volume
  53. is the control file associated with the audio port.
  54. Each input and output source has an associated stereo volume control,
  55. ranging from 0 (quiet) to 100 (loud).
  56. In addition, there are controls for the sampling rate of the D/A and A/D converters
  57. and for any tone controls.
  58. Reads
  59. return lines of the form
  60. .IP
  61. .I source
  62. .B in left
  63. .I value
  64. .B right
  65. .I value
  66. .B out left
  67. .I value
  68. .B right
  69. .I value
  70. .PP
  71. possibly abbreviated if the values are shared or non-existent.
  72. For example, if all of the values are shared, the form degenerates to
  73. .RI ` source
  74. .IR value '.
  75. Valid sources depend on the particular audio device,
  76. though all devices have an
  77. .B audio
  78. stereo source, which controls the output volume from the D/A converter
  79. connected to
  80. .BR audio .
  81. .PP
  82. Writes accept the same format with same abbreviations.
  83. Writing the string
  84. .B reset
  85. sets all of the attributes to their default value,
  86. and if no attribute is supplied,
  87. .B audio
  88. is assumed.
  89. .PP
  90. The Sound Blaster 16 (or MCD) is half-duplex and accepts the following controls on its
  91. .B volume
  92. file,
  93. in the format shown above for reads.
  94. .TF "\fLspeaker in out"
  95. .TP
  96. .B audio out
  97. Data written to audio.
  98. .TP
  99. .B synth in out
  100. MIDI synthesizer.
  101. .TP
  102. .B cd in out
  103. CD player.
  104. .TP
  105. .B line in out
  106. Line-level input.
  107. .TP
  108. .B mic in out
  109. Monaural microphone input.
  110. .TP
  111. .B speaker in out
  112. Monaural internal speaker connection.
  113. .TP
  114. .B treb out
  115. Stereo treble tone control.
  116. Values less than 50 decrease the treble,
  117. those greater increase it.
  118. .TP
  119. .B bass out
  120. Stereo bass tone control.
  121. .TP
  122. .B speed in out
  123. Sampling rate for the D/A and A/D converters,
  124. expressed in Hz.
  125. Defaults to 44100.
  126. .SH SOURCE
  127. .B /sys/src/9/port/devaudio.c
  128. .SH SEE ALSO
  129. .IR usb (4)