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## Copyright (C) 1995-2015 John W. Eaton
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING.  If not, see
## <http://www.gnu.org/licenses/>.

## -*- texinfo -*-
## @deftypefn {Function File} {} mu2lin (@var{x}, @var{n})
## Convert audio data from mu-law to linear.
##
## Mu-law values are 8-bit unsigned integers.  Linear values use @var{n}-bit
## signed integers or floating point values in the range -1@leq{}y@leq{}1 if
## @var{n} is 0.
##
## If @var{n} is not specified it defaults to 0.
## @seealso{lin2mu}
## @end deftypefn

## Author:  Andreas Weingessel <Andreas.Weingessel@ci.tuwien.ac.at>
## Created: 18 October 1994
## Adapted-By: jwe

function y = mu2lin (x, n = 0)

  if (nargin == 2)
    if (n != 0 && n != 8 && n != 16)
      error ("mu2lin: N must be either 0, 8, or 16");
    endif
  elseif (nargin != 1)
    print_usage ();
  endif

  ulaw = [32124, 31100, 30076, 29052, 28028, 27004, 25980, 24956, ...
          23932, 22908, 21884, 20860, 19836, 18812, 17788, 16764, ...
          15996, 15484, 14972, 14460, 13948, 13436, 12924, 12412, ...
          11900, 11388, 10876, 10364,  9852,  9340,  8828,  8316, ...
           7932,  7676,  7420,  7164,  6908,  6652,  6396,  6140, ...
           5884,  5628,  5372,  5116,  4860,  4604,  4348,  4092, ...
           3900,  3772,  3644,  3516,  3388,  3260,  3132,  3004, ...
           2876,  2748,  2620,  2492,  2364,  2236,  2108,  1980, ...
           1884,  1820,  1756,  1692,  1628,  1564,  1500,  1436, ...
           1372,  1308,  1244,  1180,  1116,  1052,   988,   924, ...
            876,   844,   812,   780,   748,   716,   684,   652, ...
            620,   588,   556,   524,   492,   460,   428,   396, ...
            372,   356,   340,   324,   308,   292,   276,   260, ...
            244,   228,   212,   196,   180,   164,   148,   132, ...
            120,   112,   104,    96,    88,    80,    72,    64, ...
             56,    48,    40,    32,    24,    16,     8,     0 ];

  ulaw = [ -ulaw, ulaw ];

  ## Set the shape of y to that of x overwrites the contents of y with
  ## ulaw of x.
  y = x;
  y(:) = ulaw(x + 1);

  ## Convert to real or 8-bit.
  if (n == 0)
    ## [ -32768, 32767 ] -> [ -1, 1)
    y = y/32768;
  elseif (n == 8)
    ld = max (abs (y (:)));
    if (ld < 16384 && ld > 0)
      sc = 64 / ld;
    else
      sc = 1 / 256;
    endif
    y = fix (y * sc);
  endif

endfunction
author	Rik <rik@octave.org>
date	Sun, 03 May 2015 09:36:20 -0700
parents	9fc020886ae9
children