tfrstft.m

matlab短时傅利叶变换的程序！ 自己改编的

% M-file,tfrstft.m
function [tfr,t,f] = tfrstft(x,t,N,h,trace);
[xrow,xcol] = size(x);
if (nargin < 1),
 error('At least 1 parameter is required');
elseif (nargin <= 2),
 N=xrow;
end;

hlength=floor(N/4);
hlength=hlength+1-rem(hlength,2);

if (nargin == 1),
 t=1:xrow; h = window(hlength); trace = 0;
elseif (nargin == 2) | (nargin == 3),
 h = window(hlength); trace = 0;
elseif (nargin == 4),
 trace = 0;
end;

if (N<0),
 error('N must be greater than zero');
end;
[trow,tcol] = size(t);
if (xcol~=1),
 error('X must have one column');
elseif (trow~=1),
 error('T must only have one row'); 
elseif (2^nextpow2(N)~=N),
 fprintf('For a faster computation, N should be a power of two\n');
end; 

[hrow,hcol]=size(h); Lh=(hrow-1)/2; 
if (hcol~=1)|(rem(hrow,2)==0),
 error('H must be a smoothing window with odd length');
end;

h=h/norm(h);

tfr= zeros (N,tcol) ;  
if trace, disp('Short-time Fourier transform'); end;
for icol=1:tcol,
 ti= t(icol); tau=-min([round(N/2)-1,Lh,ti-1]):min([round(N/2)-1,Lh,xrow-ti]);
 indices= rem(N+tau,N)+1; 
 if trace, disprog(icol,tcol,10); end;
 tfr(indices,icol)=x(ti+tau,1).*conj(h(Lh+1+tau));
end;
tfr=fft(tfr); 
if trace, fprintf('\n'); end;

if (nargout==0),
 tfrqview(abs(tfr).^2,x,t,'tfrstft',h);
elseif (nargout==3),
 f=fftshift(0.5*(-N:N-1)/N)';
end;