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25
26## -*- texinfo -*-
27## @deftypefn {} {@var{y} =} mu2lin (@var{x}, @var{n})
28## Convert audio data from mu-law to linear.
29##
30## Mu-law values are 8-bit unsigned integers.  Linear values use @var{n}-bit
31## signed integers or floating point values in the range -1 @leq{} @var{y}
32## @leq{} 1 if @var{n} is 0.
33##
34## If @var{n} is not specified it defaults to 0.
35## @seealso{lin2mu}
36## @end deftypefn
37
38function y = mu2lin (x, n = 0)
39
40  if (nargin == 2)
41    if (n != 0 && n != 8 && n != 16)
42      error ("mu2lin: N must be either 0, 8, or 16");
43    endif
44  elseif (nargin != 1)
45    print_usage ();
46  endif
47
48  ulaw = [32124, 31100, 30076, 29052, 28028, 27004, 25980, 24956, ...
49          23932, 22908, 21884, 20860, 19836, 18812, 17788, 16764, ...
50          15996, 15484, 14972, 14460, 13948, 13436, 12924, 12412, ...
51          11900, 11388, 10876, 10364,  9852,  9340,  8828,  8316, ...
52           7932,  7676,  7420,  7164,  6908,  6652,  6396,  6140, ...
53           5884,  5628,  5372,  5116,  4860,  4604,  4348,  4092, ...
54           3900,  3772,  3644,  3516,  3388,  3260,  3132,  3004, ...
55           2876,  2748,  2620,  2492,  2364,  2236,  2108,  1980, ...
56           1884,  1820,  1756,  1692,  1628,  1564,  1500,  1436, ...
57           1372,  1308,  1244,  1180,  1116,  1052,   988,   924, ...
58            876,   844,   812,   780,   748,   716,   684,   652, ...
59            620,   588,   556,   524,   492,   460,   428,   396, ...
60            372,   356,   340,   324,   308,   292,   276,   260, ...
61            244,   228,   212,   196,   180,   164,   148,   132, ...
62            120,   112,   104,    96,    88,    80,    72,    64, ...
63             56,    48,    40,    32,    24,    16,     8,     0 ];
64
65  ulaw = [ -ulaw, ulaw ];
66
67  ## Set the shape of y to that of x overwrites the contents of y with
68  ## ulaw of x.
69  y = x;
70  y(:) = ulaw(x + 1);
71
72  ## Convert to real or 8-bit.
73  if (n == 0)
74    ## [ -32768, 32767 ] -> [ -1, 1)
75    y /= 32768;
76  elseif (n == 8)
77    ld = max (abs (y (:)));
78    if (ld < 16384 && ld > 0)
79      sc = 64 / ld;
80    else
81      sc = 1 / 256;
82    endif
83    y = fix (y * sc);
84  endif
85
86endfunction
87