Find position of smaller waveform within a longer noise waveform.

2012 4 18
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I am searching for a short waveform within a longer noisy waveform. What is the best way to find the location within the longer waveform of the best fitting match to the short waveform? I have played with xcorr and conv and look for position of maximum value, but translating from the position in the xcorr result to the position in the long waveform is causing me problems. I also have problems if the amplitude in the long waveform varies widely from position to position.

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Thomas
Thomas 2012-4-18
is your smaller waveform (all points) exactly as is in the bigger waveform?
Philip
Philip 2012-4-18
No, there is additive noise in the longer waveform.
Thomas
Thomas 2012-4-18
Can you show what you have done so far?
Philip
Philip 2012-4-18
% vmatch is short waveform
% v is longer noisy waveform containing vmatch
tmp=xcorr(vmatch,v);
[maxxc,maxitmp]=max(tmp);
t_start=max(length(v),length(sbvmatch))-maxitmp;

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You can try the following:
Normalize your sequences as shown below:
v = (v - mean(v))/std(v,1);
Make the two sequences of equal length by zero padding and use:
[C,lag] = xcorr(v,vmatch,'unbiased')

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Philip
Philip
2012-4-18

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