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maint: Update copyright notices for release.
author John W. Eaton <jwe@octave.org>
date Wed, 23 Oct 2013 22:09:27 -0400
parents 6ed0a8532bcf
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1 ## Copyright (C) 1995-2013 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 3 of the License, or (at
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8 ## your option) 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, see
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17 ## <http://www.gnu.org/licenses/>.
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18
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19 ## -*- texinfo -*-
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20 ## @deftypefn {Function File} {@var{y} =} stft (@var{x})
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21 ## @deftypefnx {Function File} {@var{y} =} stft (@var{x}, @var{win_size})
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22 ## @deftypefnx {Function File} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc})
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23 ## @deftypefnx {Function File} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc}, @var{num_coef})
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24 ## @deftypefnx {Function File} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc}, @var{num_coef}, @var{win_type})
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25 ## @deftypefnx {Function File} {[@var{y}, @var{c}] =} stft (@dots{})
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26 ## Compute the short-time Fourier transform of the vector @var{x} with
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27 ## @var{num_coef} coefficients by applying a window of @var{win_size} data
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28 ## points and an increment of @var{inc} points.
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29 ##
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30 ## Before computing the Fourier transform, one of the following windows
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31 ## is applied:
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32 ##
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33 ## @table @asis
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34 ## @item @qcode{"hanning"}
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35 ## win_type = 1
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36 ##
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37 ## @item @qcode{"hamming"}
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38 ## win_type = 2
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39 ##
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40 ## @item @qcode{"rectangle"}
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41 ## win_type = 3
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42 ## @end table
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43 ##
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44 ## The window names can be passed as strings or by the @var{win_type} number.
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45 ##
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46 ## The following defaults are used for unspecifed arguments:
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47 ## @var{win_size} = 80, @var{inc} = 24, @var{num_coef} = 64, and
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48 ## @var{win_type} = 1.
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49 ##
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50 ## @code{@var{y} = stft (@var{x}, @dots{})} returns the absolute values
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51 ## of the Fourier coefficients according to the @var{num_coef} positive
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52 ## frequencies.
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53 ##
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54 ## @code{[@var{y}, @var{c}] = stft (@code{x}, @dots{})} returns the
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55 ## entire STFT-matrix @var{y} and a 3-element vector @var{c} containing
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56 ## the window size, increment, and window type, which is needed by the
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57 ## @code{synthesis} function.
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58 ## @seealso{synthesis}
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59 ## @end deftypefn
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60
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61 ## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at>
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62 ## Description: Short-Time Fourier Transform
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63
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64 function [y, c] = stft (x, win_size = 80, inc = 24, num_coef = 64, win_type = 1)
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65
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66 if (nargin < 1 || nargin > 5)
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67 print_usage ();
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68 endif
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69
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70 if (ischar (win_type))
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71 switch (tolower (win_type))
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72 case "hanning" win_type = 1;
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73 case "hamming" win_type = 2;
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74 case "rectangle" win_type = 3;
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75 otherwise
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76 error ("stft: unknown window type '%s'", win_type);
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77 endswitch
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78 endif
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79
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80 ## Check whether X is a vector.
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81 if (! isvector (x))
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82 error ("stft: X must be a vector");
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83 endif
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84 x = x(:);
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85
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86 ncoef = 2 * num_coef;
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87 if (win_size > ncoef)
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88 win_size = ncoef;
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89 printf ("stft: window size adjusted to %f\n", win_size);
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90 endif
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91 num_win = fix ((rows (x) - win_size) / inc);
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92
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93 ## compute the window coefficients
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94 switch (win_type)
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95 case 1 win_coef = hanning (win_size);
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96 case 2 win_coef = hamming (win_size);
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97 case 3 win_coef = ones (win_size, 1);
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98 endswitch
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99
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100 ## Create a matrix Z whose columns contain the windowed time-slices.
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101 z = zeros (ncoef, num_win + 1);
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102 start = 1;
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103 for i = 0:num_win
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104 z(1:win_size, i+1) = x(start:start+win_size-1) .* win_coef;
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105 start = start + inc;
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106 endfor
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107
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108 y = fft (z);
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109
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110 if (nargout == 1)
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111 y = abs (y(1:num_coef, :));
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112 else
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113 c = [win_size, inc, win_type];
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114 endif
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115
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116 endfunction
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117