# Detection of similar segments of two signal [closed]

I have two signals, the first is a reference signal from which I selected a segment.

I'm trying to find which segment of the other signal is the most similar to this selected segment.

I'd be glad to have some ideas.

## closed as too broad by Marcus Müller, MBaz, Peter K.♦Nov 13 '16 at 18:32

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• Welcome to DSP.SE! What have you tried? What doesn't work about it? – Peter K. Apr 6 '16 at 13:46
• I guess you want find cross correlation. Read about it and come back if you have problem, but only after trying something from your side. – user3219492 Apr 6 '16 at 14:39

You could use correlation between the two signals or a matched filter in which you set the filter coefficients as the samples from the selected segment inverted in time. In matlab it would be something like

coef = knownSegment (end:-1:1,:);

minSize = length(other_signal) + length(knownSegment) - 1;
N = 2^nextpow2(minSize);
OUT = ifft(fft(other_signal,N).*fft(coef,N));


Then you find the maximum value of variable OUT and at that point in time the two signals are most similar

• wouldn't be possible to use the function xcorr instead of the ifft? – Behind The Sciences Apr 7 '16 at 6:07
• yes, xcorr is equivalent you would have to perform xcorr(other_signal,knownSegment), notice that here you don't have to invert any signal as xcorr automatically does that for you. I didn't suggest xcorr before because it's a built-in matlab function – VMMF Apr 7 '16 at 15:56