conv from conv function and ifft
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I am trying to find the conv for a specific impulse and signal. Now when I try to use the conv function I ge the answer I need. But when I try to find fft for the impulse and then fft for the signal then .* both fft then ifft the answer I get a different answer. I tried many times any idea why?
Thanks in advance.
回答（1 个）
Matt J
2021-1-2
0 个投票
Most likely a zero-padding problem.
9 个评论
Omar Abulayla
2021-1-2
编辑：Image Analyst
2021-1-2
Matt J
2021-1-2
N=(l1+l2-1);
Omar Abulayla
2021-1-2
Matt J
2021-1-2
The length has to be l1+l2-1 because that is the expected length of the output with conv().
Omar Abulayla
2021-1-2
The error has nothing to do with the code you've shown, or my proposed modification:
x=rand(1,3); h=rand(1,5);
l1=length(x); l2=length(h);
N=l1+l2-1;
xpad=[x zeros(1,N-l1)];
hpad=[h zeros(1,N-l2)];
ccirc = ifft(fft(xpad).*fft(hpad))
Image Analyst
2021-1-2
This works fine, so what did you do?
fprintf('Beginning to run %s.m ...\n', mfilename);
% Make random signal.
signalLength = 32;
x = rand(1, signalLength);
% Make impulse function:
h = zeros(1, signalLength);
h(signalLength/2) = 1;
% Pad the signal and kernel.
l1=length(x)
l2=length(h)
N = max(l1,l2)
xpad=[x, zeros(1,N-l1)];
hpad=[h, zeros(1,N-l2)];
ccirc = ifft(fft(xpad).*fft(hpad));
fprintf('Done running %s.m.\n', mfilename);
Matt J
2021-1-2
Looks fine. No error messages.
Please post your code in code wells, so that it can be more easily read, copied, and run.
Aside from that, why are we talking about your early version that doesn't incorporate my modification? I've already told you that that version had insufficient zero-padding for that to work.
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2021-1-2
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