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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, 59 Temple Place - Suite 330, Boston, MA |
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18 ## 02111-1307, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} mu2lin (@var{x}, @var{bps}) |
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22 ## If the vector @var{x} represents mono audio data in mu-law encoding, |
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23 ## @code{mu2lin} converts it to linear encoding. The optional argument |
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24 ## @var{bps} specifies whether the input data uses 8 bit per sample |
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25 ## (default) or 16 bit. |
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26 ## @end deftypefn |
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27 ## @seealso{lin2mu, loadaudio, saveaudio, playaudio, setaudio, record} |
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28 |
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29 ## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at> |
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30 ## Created: 18 October 1994 |
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31 ## Adapted-By: jwe |
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32 |
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33 function y = mu2lin (x, bit) |
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34 |
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35 if (nargin == 1) |
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36 bit = 8; |
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37 elseif (nargin == 2) |
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38 if (bit != 8 && bit != 16) |
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39 error ("mu2lin: bit must be either 8 or 16"); |
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40 endif |
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41 else |
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42 usage ("y = mu2lin (x [, bit])"); |
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43 endif |
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44 |
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45 if (! is_vector (x)) |
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46 error ("mu2lin: x must be a vector"); |
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47 endif |
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48 |
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49 exp_lut = [0; 132; 396; 924; 1980; 4092; 8316; 16764]; |
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50 |
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51 ## invert x bitwise |
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52 x = 255 - x; |
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53 |
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54 ## determine sign of y |
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55 sig = (x > 127); |
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56 |
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57 ## determine exponent and fraction of y |
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58 e = fix (x / 16) - 8 .* sig + 1; |
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59 f = rem (x, 16); |
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60 |
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61 sig = 1 - 2 .* sig; |
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62 y = (pow2 (f, e + 2) + exp_lut (e)) .* sig; |
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63 |
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64 ## convert to 8-bit |
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65 if (bit == 8) |
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66 ld = max (abs (y)); |
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67 if (ld < 16384) |
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68 sc = 64 / ld; |
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69 else |
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70 sc = 1 / 256; |
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71 endif |
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72 y = fix (y * sc); |
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73 endif |
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74 |
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75 endfunction |
