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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 |
