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########################################################################
##
## Copyright (C) 1995-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## 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
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{y} =} mu2lin (@var{x})
## @deftypefnx {} {@var{y} =} mu2lin (@var{x}, @var{n})
## Convert audio data from mu-law to linear.
##
## Mu-law values are 8-bit unsigned integers in the range 0 @leq{} @var{y}
## @leq{} 255. Linear values use floating point values in the range
## -@var{linmax} @leq{} @var{x} @var{linmax} (where
## @code{@var{linmax} = 32124/32768 =~ 0.98}) when @var{n} is zero (default).
## If @var{n} is 8 or 16 then @var{n}-bit signed integers are used instead.
##
## Programming Note: @code{mu2lin} maps maximum mu-law inputs to values
## slightly below the maximum ([-0.98, +0.98]) representable with a linear
## scale. Because of this, @code{mu2lin (lin2mu (@var{x}))} might not
## reproduce the original input.
## @seealso{lin2mu}
## @end deftypefn
function y = mu2lin (x, n = 0)
if (nargin < 1)
print_usage ();
endif
if (nargin == 2)
if (! isscalar (n) && ! isreal (n)
|| (n != 0 && n != 8 && n != 16))
error ("lin2mu: N must be either 0, 8, or 16");
elseif (isempty (n))
n = 0;
endif
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 /= 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
## Test functionality
%!shared linmax
%! linmax = 32124 / 32768;
%!test
%! x = [0, 128, 255];
%! y = x';
%! assert (mu2lin (x), (mu2lin (y))');
%! assert (mu2lin (x), [-linmax, +linmax, 0]);
%!assert (mu2lin ([]), [])
%!assert (mu2lin (255), 0)
%!assert (mu2lin (255, 0), 0)
%!assert (mu2lin (255, 8), 0)
%!assert (mu2lin (255, 16), 0)
%!assert (mu2lin (128, []), linmax)
%!assert (mu2lin (128, 8), 125)
%!assert (mu2lin (128, 16), 32124)
%!assert (mu2lin (zeros (1, 1000), 0), repmat (-linmax, 1, 1000))
%!assert (mu2lin (255*ones (2, 2), 0), zeros (2, 2))
## Test input validation
%!error <Invalid call> mu2lin ()
%!error <N must be either 0, 8, or 16> mu2lin (1, 2)
%!error <N must be either 0, 8, or 16> mu2lin (1, [1,2])
%!error <N must be either 0, 8, or 16> mu2lin (1, ones (1, 2))
%!error mu2lin ({2:5})
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