Reply by Egler, Mark August 31, 20042004-08-31
Divya,

You probably figured this out by now, but they are the same, except that you
squared the fft output but not the freqz output. Try plotting sqrt(P(1:512))
and abs(h).

Mark
-----Original Message-----
From: divya_8910 [mailto:]
Sent: Friday, August 27, 2004 3:18 PM
To:
Subject: [matlab] FFT vs freqz hi,

i have a low pass filter and i plotted the frequency response using
freqz and fft and got diff plots... b=remez(102,[0 0.5 0.6 1],[1 1 0 0]);
B = fft(b,1024); P = B.*conj(B);
t=(pi/512)*[0:511];
figure(1);
semilogy(t,P(1:512),'Color',[1 0 0.4975]); hold on;

[h,w]=freqz(b,1,1024);
semilogy(w,abs(h)); hold off;

can anyone tell me why tht happens..i thought freqz uses the fft
algorithm

thx
divya _____________________________________
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Reply by divya_8910 August 27, 20042004-08-27
hi,

i have a low pass filter and i plotted the frequency response using
freqz and fft and got diff plots... b=remez(102,[0 0.5 0.6 1],[1 1 0 0]);
B = fft(b,1024); P = B.*conj(B);
t=(pi/512)*[0:511];
figure(1);
semilogy(t,P(1:512),'Color',[1 0 0.4975]); hold on;

[h,w]=freqz(b,1,1024);
semilogy(w,abs(h)); hold off;

can anyone tell me why tht happens..i thought freqz uses the fft
algorithm

thx
divya