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1 ## Copyright (C) 1996, 1997 John W. Eaton |
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2 ## |
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3 ## This file is part of Octave. |
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4 ## |
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5 ## Octave is free software; you can redistribute it and/or modify it |
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6 ## under the terms of the GNU General Public License as published by |
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7 ## the Free Software Foundation; either version 2, or (at your option) |
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8 ## any later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but |
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 ## General Public License for more details. |
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14 ## |
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15 ## You should have received a copy of the GNU General Public License |
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16 ## along with Octave; see the file COPYING. If not, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} lin2mu (@var{x}, @var{n}) |
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22 ## Converts audio data from linear to mu-law. Mu-law values use 8-bit |
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23 ## unsigned integers. Linear values use @var{n}-bit signed integers or |
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24 ## floating point values in the range -1<=@var{x}<=1 if @var{n} is 0. |
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25 ## If @var{n} is not specified it defaults to 0, 8 or 16 depending on |
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26 ## the range values in @var{x}. |
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27 ## @end deftypefn |
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28 ## |
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29 ## @seealso{mu2lin, loadaudio, saveaudio, playaudio, setaudio, and record} |
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30 |
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31 ## Author: Andreas Weingessel <Andreas.Weingessel@ci.tuwien.ac.at> |
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32 ## Created: 17 October 1994 |
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33 ## Adapted-By: jwe |
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34 |
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35 function y = lin2mu (x, bit) |
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36 |
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37 if (nargin == 1) |
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38 range = max (abs (x (:))); |
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39 if (range <= 1) |
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40 bit = 0; |
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41 elseif (range <= 128) |
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42 bit = 8; |
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43 warning ("lin2mu: no precision specified, so using %d", bit); |
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44 else |
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45 bit = 16; |
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46 endif |
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47 elseif (nargin == 2) |
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48 if (bit != 0 && bit != 8 && bit != 16) |
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49 error ("lin2mu: bit must be either 0, 8 or 16"); |
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50 endif |
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51 else |
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52 usage ("y = lin2mu (x, bit)"); |
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53 endif |
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54 |
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55 ## Transform real and n-bit format to 16-bit. |
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56 if (bit == 0) |
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57 ## [-1,1] -> [-32768, 32768] |
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58 x = 32768 * x; |
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59 elseif (bit != 16) |
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60 x = 2^(16-bit) .* x; |
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61 endif |
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62 |
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63 ## Determine sign of x, set sign(0) = 1. |
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64 sig = sign(x) + (x == 0); |
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65 |
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66 ## Take absolute value of x, but force it to be smaller than 32636; |
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67 ## add bias. |
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68 x = min (abs (x), 32635) + 132; |
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69 |
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70 ## Find exponent and fraction of bineary representation. |
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71 [f, e] = log2 (x); |
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72 |
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73 y = 64 * sig - 16 * e - fix (32 * f) + 335; |
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74 |
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75 endfunction |
