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Math Forum » Discussions » Software » comp.soft-sys.matlab

Topic: Noisy fft
Replies: 2 Last Post: Jan 31, 2013 2:44 AM

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Peter Mairhofer

Posts: 23
Registered: 8/18/10

Noisy fft
Posted: Jan 30, 2013 11:41 PM

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Hi,

I create a signal x, let it through an FIR filter to create y. Then I
divide the spectra and I should obtain the frequency response of the
filter. However, what I get is very/noo noisy:
http://snag.gy/7Quwn.jpg

The code is:
N = 1000;
h_orig = [1 0.75 0.5];
H_orig = fft([h_orig.' ; zeros(N-length(h_orig), 1)]);
x = randn(N, 1);
y = filter(h_orig, 1, x);
H = fft(y) ./ fft(x);
plot(abs([H_orig, H]));

Can someone explain this?

Thanks,
Peter

Date

Subject

Author

1/30/13

Noisy fft

Peter Mairhofer

1/31/13

Re: Noisy fft

dbd

1/31/13

Re: Noisy fft

Bruno Luong

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