www.pudn.com > voiceprocessingtoolbox.rar > fftApproximate01.m

% This example demos the effect of square wave approximation by DFT 
 
figure 
L = 15; N = 25; 
x = [ones(1,L), zeros(1,N-L)]; 
frameSize=length(x); 
 
runNum=3; 
for i=1:runNum, 
	pointNum=ceil(frameSize/(2*runNum)*i);	% Actually 2*pointNum-1 coefs are taken 
	X = fft(x); 
	magX = abs(X); 
 
	remainIndex=[1:pointNum, frameSize-pointNum+2:frameSize]; 
	X2=0*X; 
	X2(remainIndex)=X(remainIndex); 
	x2=ifft(X2); 
	x2=real(x2); 
 
	subplot(3,2,2*i-1); 
	stem(x); 
	hold on 
	plot(x2, 'r'); 
	hold off 
	title(sprintf('x[n] and %d-points approximation', 2*pointNum-1)); 
	axis([-inf,inf,-0.5,1.5]) 
 
	subplot(3,2,2*i); 
	shiftedMagX=fftshift(magX); 
	plot(shiftedMagX, '.-'); axis tight 
	title('DFS of x[n]') 
	hold on 
	temp=ifftshift(1:frameSize); 
	ind=temp(remainIndex); 
	plot(ind, shiftedMagX(ind), 'or'); grid on 
	hold off 
end