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NAME
     audio_u2c,  audio_u2s,  audio_u2l,   audio_c2u,   audio_s2u,
     audio_l2u,   audio_a2c,   audio_a2s,  audio_a2l,  audio_c2a,
     audio_s2a, audio_l2a, audio_a2u, audio_u2a  -  u-law,  A-law
     and linear data conversions

SYNOPSIS
     #include <multimedia/libaudio.h>

     char audio_u2c(ulaw)
     unsigned char ulaw;

     short audio_u2s(ulaw)
     unsigned char ulaw;

     long audio_u2l(ulaw)
     unsigned char ulaw;

     unsigned char audio_c2u(pcm)
     char pcm;

     unsigned char audio_s2u(pcm)
     short pcm;

     unsigned char audio_l2u(pcm)
     long pcm;

     char audio_a2c(alaw)
     unsigned char alaw;

     short audio_a2s(alaw)
     unsigned char alaw;

     long audio_a2l(alaw)
     unsigned char alaw;

     unsigned char audio_c2a(pcm)
     char pcm;

     unsigned char audio_s2a(pcm)
     short pcm;

     unsigned char audio_l2a(pcm)
     long pcm;

     unsigned char audio_a2u(alaw)
     unsigned char alaw;

     unsigned char audio_u2a(ulaw)
     unsigned char ulaw;


DESCRIPTION
     These macros are designed to make  conversions  between  the
     8-bit  u-law,  A-law  and  8-,  16- 32-bit linear Pulse Code
     Modulated (PCM) values as defined in the CCITT  G.711  stan-
     dards.  The u-law and A-law compandings allow linear data to
     be compressed to 8 bits.  All  the  conversions  are  imple-
     mented  with  lookup  tables for fast operations.  The u-law
     and A-law data have 14-bit and 13-bit dynamic ranges respec-
     tively.  Only the most significant bits in the 16- or 32-bit
     linear PCM values are used for  compression  and  decompres-
     sion.

     The u-law and A-law transfer functions result  in  a  nearly
     linear  relationship  to  PCM  at low amplitudes and a loga-
     rithmic relationship at high amplitudes.  Thus,  it  is  not
     reasonable  to  perform arithmetic operations (such as would
     be performed on PCM data) directly on the encoded data.  For
     instance,  to  sum  two u-law or A-law values, the following
     lines of code will give very different answers:
          wrong = (ulaw1 + ulaw2);
          right = audio_s2u(audio_u2s(ulaw1) + audio_u2s(ulaw2));

          wrong = (alaw1 + alaw2);
          right = audio_s2a(audio_a2s(alaw1) + audio_a2s(alaw2));

     audio_u2c(), audio_u2s(), and audio_u2l() convert u-law data
     to  PCM  signed integers of 8, 16, or 32 bits.  audio_a2c(),
     audio_a2s(), and  audio_a2l()  convert  A-law  data  to  PCM
     signed integers of 8, 16, or 32 bits.  Since u-law and A-law
     data represents approximately 13 bits of precision to  begin
     with,  the  conversion  to  8-bit  integers loses precision,
     while the conversion to 32-bit integers is  provided  merely
     as a convenience.

     audio_c2u(),    audio_s2u(),    audio_l2u(),    audio_c2a(),
     audio_s2a(), and audio_l2a() convert 8-, 16-, and 32-bit PCM
     signed integers to their u-law or A-law encoded form.

     audio_a2u(), and audio_u2a() do the conversions  between  u-
     law  and  A-law  data.   Both u-law and A-law data are 8-bit
     wide.  These conversions do not have advantages in  compres-
     sion  or arithmetic operations.  They are used when an audio
     file is recorded in one form and played in the other form.

SEE ALSO
     audio_convert(3), audio_g721(3), audio_g723(3).

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