Forums

FFT vs freqz

Started by divya_8910 August 27, 2004
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



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 _____________________________________
Note: If you do a simple "reply" with your email client, only the author of
this message will receive your answer. You need to do a "reply all" if you
want your answer to be distributed to the entire group.

_____________________________________
About this discussion group:

To Join:

To Post:

To Leave:

Archives: http://www.yahoogroups.com/group/matlab

More DSP-Related Groups: http://www.dsprelated.com/groups.php3
Yahoo! Groups Links