## Copyright (C) 1995, 1996, 1997 Andreas Weingessel ## ## This program is free software; you can redistribute it and/or modify ## it under the terms of the GNU General Public License as published by ## the Free Software Foundation; either version 2, or (at your option) ## any later version. ## ## This program is distributed in the hope that it will be useful, but ## WITHOUT ANY WARRANTY; without even the implied warranty of ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU ## General Public License for more details. ## ## You should have received a copy of the GNU General Public License ## along with this file. If not, write to the Free Software Foundation, ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. ## usage: [Y, c] = stft (X [, win_size [, inc [, num_coef [, w_type]]]]) ## ## Computes the short-term Fourier transform of the vector X with ## "num_coef" coefficients by applying a window of "win_size" data ## points and an increment of "inc" points. ## ## Before computing the Fourier transform, one of the following windows ## is applied: "hanning" (w_type = 1), "hamming" (w_type = 2), ## "rectangle" (w_type = 3). The window names can be passed as strings ## or by the w_type number. ## ## If not all arguments are specified, the following defaults are used: ## win_size = 80, inc = 24, num_coef = 64, w_type = 1. ## ## Y = stft (X [, ...]) returns the absolute values of the Fourier ## coefficients according to the num_coef positive frequencies. ## [Y, c] = stft (X [, ...]) returns the entire STFT-matrix Y and a ## vector c = [win_size, inc, w_type] which is needed by the synthesis ## function. ## Author: AW <Andreas.Weingessel@ci.tuwien.ac.at> ## Description: Short-term Fourier transform function [Y, c] = stft(X, win, inc, coef, w_type) ## default values of unspecified arguments if (nargin < 5) w_type = 1; if (nargin < 4) coef = 64; if (nargin < 3) inc = 24; if (nargin < 2) win = 80; endif endif endif elseif (nargin == 5) if (isstr (w_type)) if (strcmp (w_type, "hanning")) w_type = 1; elseif (strcmp (w_type, "hamming")) w_type = 2; elseif (strcmp (w_type, "rectangle")) w_type = 3; else error (["stft: unknown window type `", w_type, "'"]) endif endif else usage ("[Y [, c]] = ", ... "stft(X [, win_size [, inc [, num_coef [, w_type]]]])"); endif ## check whether X is a vector [nr, nc] = size (X); if (nc != 1) if (nr == 1) X = X'; nr = nc; else error ("stft: X must be a vector"); endif endif num_coef = 2 * coef; if (win > num_coef) win = num_coef; printf ("stft: window size adjusted to %f\n", win); endif num_win = fix ((nr - win) / inc); ## compute the window coefficients if (w_type == 3) # rectangular window WIN_COEF = ones (win, 1); elseif (w_type == 2) # Hamming window WIN_COEF = hamming (win); else # Hanning window WIN_COEF = hanning (win); endif ## create a matrix Z whose columns contain the windowed time-slices Z = zeros (num_coef, num_win + 1); start = 1; for i = 0:num_win Z(1:win, i+1) = X(start:start+win-1) .* WIN_COEF; start = start + inc; endfor Y = fft (Z); if (nargout == 1) Y = abs (Y(1:coef, :)); else c = [win, inc, w_type]; endif endfunction

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