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[project @ 1998-10-23 05:43:59 by jwe]
author jwe
date Fri, 23 Oct 1998 05:44:01 +0000
parents
children f8dde1807dee
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3191
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1 ## Copyright (C) 1995, 1996, 1997 Andreas Weingessel
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2 ##
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3 ## This program is free software; you can redistribute it and/or modify
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4 ## it under the terms of the GNU General Public License as published by
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5 ## the Free Software Foundation; either version 2, or (at your option)
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6 ## any later version.
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7 ##
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8 ## This program is distributed in the hope that it will be useful, but
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9 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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10 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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11 ## General Public License for more details.
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12 ##
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13 ## You should have received a copy of the GNU General Public License
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14 ## along with this file. If not, write to the Free Software Foundation,
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15 ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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16
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17 ## usage: [Y, c] = stft (X [, win_size [, inc [, num_coef [, w_type]]]])
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18 ##
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19 ## Computes the short-term Fourier transform of the vector X with
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20 ## "num_coef" coefficients by applying a window of "win_size" data
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21 ## points and an increment of "inc" points.
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22 ##
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23 ## Before computing the Fourier transform, one of the following windows
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24 ## is applied: "hanning" (w_type = 1), "hamming" (w_type = 2),
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25 ## "rectangle" (w_type = 3). The window names can be passed as strings
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26 ## or by the w_type number.
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27 ##
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28 ## If not all arguments are specified, the following defaults are used:
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29 ## win_size = 80, inc = 24, num_coef = 64, w_type = 1.
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30 ##
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31 ## Y = stft (X [, ...]) returns the absolute values of the Fourier
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32 ## coefficients according to the num_coef positive frequencies.
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33 ## [Y, c] = stft (X [, ...]) returns the entire STFT-matrix Y and a
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34 ## vector c = [win_size, inc, w_type] which is needed by the synthesis
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35 ## function.
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36
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37 ## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at>
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38 ## Description: Short-term Fourier transform
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39
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40 function [Y, c] = stft(X, win, inc, coef, w_type)
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41
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42 ## default values of unspecified arguments
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43 if (nargin < 5)
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44 w_type = 1;
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45 if (nargin < 4)
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46 coef = 64;
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47 if (nargin < 3)
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48 inc = 24;
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49 if (nargin < 2)
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50 win = 80;
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51 endif
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52 endif
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53 endif
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54 elseif (nargin == 5)
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55 if (isstr (w_type))
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56 if (strcmp (w_type, "hanning"))
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57 w_type = 1;
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58 elseif (strcmp (w_type, "hamming"))
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59 w_type = 2;
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60 elseif (strcmp (w_type, "rectangle"))
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61 w_type = 3;
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62 else
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63 error (["stft: unknown window type `", w_type, "'"])
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64 endif
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65 endif
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66 else
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67 usage ("[Y [, c]] = ", ...
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68 "stft(X [, win_size [, inc [, num_coef [, w_type]]]])");
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69 endif
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70
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71 ## check whether X is a vector
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72 [nr, nc] = size (X);
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73 if (nc != 1)
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74 if (nr == 1)
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75 X = X';
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76 nr = nc;
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77 else
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78 error ("stft: X must be a vector");
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79 endif
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80 endif
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81
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82 num_coef = 2 * coef;
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83 if (win > num_coef)
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84 win = num_coef;
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85 printf ("stft: window size adjusted to %f\n", win);
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86 endif
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87 num_win = fix ((nr - win) / inc);
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88
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89 ## compute the window coefficients
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90 if (w_type == 3) # rectangular window
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91 WIN_COEF = ones (win, 1);
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92 elseif (w_type == 2) # Hamming window
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93 WIN_COEF = hamming (win);
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94 else # Hanning window
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95 WIN_COEF = hanning (win);
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96 endif
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97
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98 ## create a matrix Z whose columns contain the windowed time-slices
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99 Z = zeros (num_coef, num_win + 1);
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100 start = 1;
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101 for i = 0:num_win
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102 Z(1:win, i+1) = X(start:start+win-1) .* WIN_COEF;
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103 start = start + inc;
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104 endfor
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105
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106 Y = fft (Z);
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107
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108 if (nargout == 1)
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109 Y = abs (Y(1:coef, :));
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110 else
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111 c = [win, inc, w_type];
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112 endif
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113
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114 endfunction