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########################################################################
##
## Copyright (C) 1995-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave 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 3 of the License, or
## (at your option) any later version.
##
## Octave 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 Octave; see the file COPYING. If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{y} =} stft (@var{x})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc}, @var{num_coef})
## @deftypefnx {} {@var{y} =} stft (@var{x}, @var{win_size}, @var{inc}, @var{num_coef}, @var{win_type})
## @deftypefnx {} {[@var{y}, @var{c}] =} stft (@dots{})
## Compute the short-time Fourier transform of the vector @var{x} with
## @var{num_coef} coefficients by applying a window of @var{win_size} data
## points and an increment of @var{inc} points.
##
## Before computing the Fourier transform, one of the following windows
## is applied:
##
## @table @asis
## @item @qcode{"hanning"}
## win_type = 1
##
## @item @qcode{"hamming"}
## win_type = 2
##
## @item @qcode{"rectangle"}
## win_type = 3
## @end table
##
## The window names can be passed as strings or by the @var{win_type} number.
##
## The following defaults are used for unspecified arguments:
## @var{win_size} = 80, @var{inc} = 24, @var{num_coef} = 64, and
## @var{win_type} = 1.
##
## @code{@var{y} = stft (@var{x}, @dots{})} returns the absolute values of the
## Fourier coefficients according to the @var{num_coef} positive frequencies.
##
## @code{[@var{y}, @var{c}] = stft (@var{x}, @dots{})} returns the entire
## STFT-matrix @var{y} and a 3-element vector @var{c} containing the window
## size, increment, and window type, which is needed by the @code{synthesis}
## function.
## @seealso{synthesis}
## @end deftypefn
function [y, c] = stft (x, win_size = 80, inc = 24, num_coef = 64, win_type = 1)
if (nargin < 1)
print_usage ();
endif
if (ischar (win_type))
switch (lower (win_type))
case "hanning" , win_type = 1;
case "hamming" , win_type = 2;
case "rectangle" , win_type = 3;
otherwise
error ("stft: unknown window type '%s'", win_type);
endswitch
endif
## Check whether X is a vector.
if (! isvector (x))
error ("stft: X must be a vector");
endif
x = x(:);
ncoef = 2 * num_coef;
if (win_size > ncoef)
win_size = ncoef;
printf ("stft: window size adjusted to %f\n", win_size);
endif
num_win = fix ((rows (x) - win_size) / inc);
## compute the window coefficients
switch (win_type)
case 1 , win_coef = hanning (win_size);
case 2 , win_coef = hamming (win_size);
case 3 , win_coef = ones (win_size, 1);
endswitch
## Create a matrix Z whose columns contain the windowed time-slices.
z = zeros (ncoef, num_win + 1);
start = 1;
for i = 0:num_win
z(1:win_size, i+1) = x(start:start+win_size-1) .* win_coef;
start += inc;
endfor
y = fft (z);
if (nargout == 1)
y = abs (y(1:num_coef, :));
else
c = [win_size, inc, win_type];
endif
endfunction
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