www.pudn.com > TimeFrequency.rar > Spectrogram.asv

 function specgm = Spectrogram(sig,w,m,titl) 
% Spectrogram -- Time-Varying Spectrum 
%  Usage 
%    
%  Inputs 
%    sig      1-d signal 
%    w        window half-length, default = n/2 
%    m        inter-window spacing, default=1 
%    titl     Optional Title String Modifier 
%  Outputs 
%    specgm   spectrogram 
% 
%  Side Effects 
%    Image Plot of the spectrogram 
% 
%  See Also 
%    WVDist, WVDist_AF, ImagePhasePlane 
% 
% 
	x=sig(:); 
	n = length(x); 
	f = [zeros(n,1); sig; zeros(n,1)]; 
% 
	if nargin < 2, 
		w = n/2; 
	end 
	if nargin < 3, 
		m=1; 
	end 
	if nargin < 4, 
		titl = []; 
	end 
% 
	nw     = floor(n ./ m); 
	specgm = zeros(w+1,nw); 
	ix     = ((-w+1):w); 
% 
	for l=1:nw, 
		t = 1+ (l-1)*m; 
		if m==1 & rem(t,16)==1, 
			fprintf('Spectrogram: t=%i\n',t); 
 		end 
 
		tim = n + t + ix; 
		seg = f(tim); 
		localspec = abs(fft(seg)); 
		specgm(:,l)  = localspec(1:(w+1)); 
	end 
 
% 
% Make Spectrogram Display 
 
	spmax = max(max(specgm)); 
	spmin = min(min(specgm)); 
	colormap(1-gray(256)) 
	image(linspace(0,1,n),linspace(0,1,w+1),256*(specgm-spmin)/(spmax-spmin)); 
	axis('xy') 
	xlabel('Time') 
	ylabel('Frequency') 
% 
	title(titl); 
% 
	if nargout==0, 
		specgm = []; 
	end 
 
% 
% Copyright (c) 1995, David Donoho 
% 
     
     
%    
% Part of WaveLab Version 802 
% Built Sunday, October 3, 1999 8:52:27 AM 
% This is Copyrighted Material 
% For Copying permissions see COPYING.m 
% Comments? e-mail wavelab@stat.stanford.edu 
%