function d = stft(x, f, w, h) % D = stft(X, F, W, H) Short-time Fourier transform. % Returns some frames of short-term Fourier transform of x. Each % column of the result is one F-point fft; each successive frame is % offset by H points until X is exhausted. Data is hamm-windowed % at W pts, or rectangular if W=0, or with W if it is a vector. % See also 'istft.m'. % dpwe 1994may05. Uses built-in 'fft' % \$Header: /homes/dpwe/public_html/resources/matlab/pvoc/RCS/stft.m,v 1.2 2009/01/07 04:32:42 dpwe Exp \$ s = length(x); if length(w) == 1 if w == 0 % special case: rectangular window win = ones(1,f); else if rem(w, 2) == 0 % force window to be odd-len w = w + 1; end halflen = (w-1)/2; halff = f/2; % midpoint of win halfwin = 0.5 * ( 1 + cos( pi * (0:halflen)/halflen)); win = zeros(1, f); acthalflen = min(halff, halflen); win((halff+1):(halff+acthalflen)) = halfwin(1:acthalflen); win((halff+1):-1:(halff-acthalflen+2)) = halfwin(1:acthalflen); end else win = w; w = length(w); end c = 1; % pre-allocate output array d = zeros((1+f/2),1+fix((s-f)/h)); for b = 0:h:(s-f) u = win.*x((b+1):(b+f)); t = fft(u); d(:,c) = t(1:(1+f/2))'; c = c+1; end;