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1 ## Copyright (C) 1995, 1996, 1997 Andreas Weingessel |
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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} {[@var{y}, @var{c}]} = stft (@var{x}, @var{win_size}, @var{inc}, @var{num_coef}, @var{w_type}) |
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22 ## Compute the short-term Fourier transform of the vector @var{x} with |
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23 ## @var{num_coef} coefficients by applying a window of @var{win_size} data |
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24 ## points and an increment of @var{inc} points. |
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25 ## |
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26 ## Before computing the Fourier transform, one of the following windows |
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27 ## is applied: |
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28 ## |
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29 ## @table @asis |
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30 ## @item hanning |
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31 ## w_type = 1 |
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32 ## @item hamming |
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33 ## w_type = 2 |
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34 ## @item rectangle |
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35 ## w_type = 3 |
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36 ## @end table |
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37 ## |
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38 ## The window names can be passed as strings or by the @var{w_type} number. |
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39 ## |
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40 ## If not all arguments are specified, the following defaults are used: |
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41 ## @var{win_size} = 80, @var{inc} = 24, @var{num_coef} = 64, and |
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42 ## @var{w_type} = 1. |
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43 ## |
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44 ## @code{@var{y} = stft (@var{x}, @dots{})} returns the absolute values |
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45 ## of the Fourier coefficients according to the @var{num_coef} positive |
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46 ## frequencies. |
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47 ## |
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48 ## @code{[@var{y}, @var{c}] = stft (@code{x}, @dots{})} returns the |
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49 ## entire STFT-matrix @var{y} and a 3-element vector @var{c} containing |
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50 ## the window size, increment, and window type, which is needed by the |
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51 ## synthesis function. |
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52 ## @end deftypefn |
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53 |
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54 ## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at> |
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55 ## Description: Short-term Fourier transform |
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56 |
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57 function [Y, c] = stft(X, win, inc, coef, w_type) |
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58 |
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59 ## default values of unspecified arguments |
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60 if (nargin < 5) |
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61 w_type = 1; |
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62 if (nargin < 4) |
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63 coef = 64; |
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64 if (nargin < 3) |
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65 inc = 24; |
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66 if (nargin < 2) |
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67 win = 80; |
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68 endif |
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69 endif |
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70 endif |
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71 elseif (nargin == 5) |
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72 if (ischar (w_type)) |
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73 if (strcmp (w_type, "hanning")) |
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74 w_type = 1; |
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75 elseif (strcmp (w_type, "hamming")) |
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76 w_type = 2; |
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77 elseif (strcmp (w_type, "rectangle")) |
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78 w_type = 3; |
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79 else |
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80 error ("stft: unknown window type `%s'", w_type); |
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81 endif |
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82 endif |
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83 else |
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84 usage ("[Y, c] = stft(X, win_size, inc, num_coef, w_type)"); |
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85 endif |
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86 |
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87 ## check whether X is a vector |
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88 [nr, nc] = size (X); |
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89 if (nc != 1) |
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90 if (nr == 1) |
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91 X = X'; |
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92 nr = nc; |
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93 else |
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94 error ("stft: X must be a vector"); |
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95 endif |
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96 endif |
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97 |
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98 num_coef = 2 * coef; |
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99 if (win > num_coef) |
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100 win = num_coef; |
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101 printf ("stft: window size adjusted to %f\n", win); |
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102 endif |
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103 num_win = fix ((nr - win) / inc); |
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104 |
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105 ## compute the window coefficients |
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106 if (w_type == 3) # rectangular window |
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107 WIN_COEF = ones (win, 1); |
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108 elseif (w_type == 2) # Hamming window |
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109 WIN_COEF = hamming (win); |
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110 else # Hanning window |
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111 WIN_COEF = hanning (win); |
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112 endif |
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113 |
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114 ## create a matrix Z whose columns contain the windowed time-slices |
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115 Z = zeros (num_coef, num_win + 1); |
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116 start = 1; |
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117 for i = 0:num_win |
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118 Z(1:win, i+1) = X(start:start+win-1) .* WIN_COEF; |
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119 start = start + inc; |
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120 endfor |
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121 |
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122 Y = fft (Z); |
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123 |
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124 if (nargout == 1) |
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125 Y = abs (Y(1:coef, :)); |
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126 else |
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127 c = [win, inc, w_type]; |
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128 endif |
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129 |
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130 endfunction |
