function x = istft(d, ftsize, w, h) % X = istft(D, F, W, H) Inverse short-time Fourier transform. % Performs overlap-add resynthesis from the short-time Fourier transform % data in D. Each column of D is taken as the result of an F-point % fft; each successive frame was offset by H points (default % W/2, or F/2 if W==0). Data is hann-windowed at W pts, or % W = 0 gives a rectangular window (default); % W as a vector uses that as window. % This version scales the output so the loop gain is 1.0 for % either hann-win an-syn with 25% overlap, or hann-win on % analysis and rect-win (W=0) on synthesis with 50% overlap. % dpwe 1994may24. Uses built-in 'ifft' etc. % \$Header: /home/empire6/dpwe/public_html/resources/matlab/pvoc/RCS/istft.m,v 1.5 2010/08/12 20:39:42 dpwe Exp \$ if nargin < 2; ftsize = 2*(size(d,1)-1); end if nargin < 3; w = 0; end if nargin < 4; h = 0; end % will become winlen/2 later s = size(d); if s(1) ~= (ftsize/2)+1 error('number of rows should be fftsize/2+1') end cols = s(2); if length(w) == 1 if w == 0 % special case: rectangular window win = ones(1,ftsize); else if rem(w, 2) == 0 % force window to be odd-len w = w + 1; end halflen = (w-1)/2; halff = ftsize/2; halfwin = 0.5 * ( 1 + cos( pi * (0:halflen)/halflen)); win = zeros(1, ftsize); acthalflen = min(halff, halflen); win((halff+1):(halff+acthalflen)) = halfwin(1:acthalflen); win((halff+1):-1:(halff-acthalflen+2)) = halfwin(1:acthalflen); % 2009-01-06: Make stft-istft loop be identity for 25% hop win = 2/3*win; end else win = w; end w = length(win); % now can set default hop if h == 0 h = floor(w/2); end xlen = ftsize + (cols-1)*h; x = zeros(1,xlen); for b = 0:h:(h*(cols-1)) ft = d(:,1+b/h)'; ft = [ft, conj(ft([((ftsize/2)):-1:2]))]; px = real(ifft(ft)); x((b+1):(b+ftsize)) = x((b+1):(b+ftsize))+px.*win; end;