After aligning two signals using xcorr, how to make both signals (varying) lengths equal?

Hello,

I am using xcorr to synchronize two signals (S1, S2; from two different devices) of the same event. The function works well and signals get aligned. However, given that signals' length are not consistently equal (sometimes numel(S1) > numel(S2) and viceversa), I am struggling to efficiently clean the longest signal (at the beginning and / or at the end) and have the two signals aligned, with equal lengths.

Here is the code I am using:

      [C22, lag22] = xcorr(S1, S2);
      [M22,I22] = max(C22);
      t22 = lag22(I22);
    figure(1), plot(1:length(S1), S1, 'b', 1+t22:length(S2)+t22, S2, 'r'), title('S1 and S2 "Synch"')

How could I follow to make both S1 and S2 lengths equal, having into account that I am not aware of which signal will be longer at each particular case?

I really appreciate any help on this.

Thanks Antonio

[Image Analyst]

You forgot to attach examples of S1 and S2. Come on, make it easy for us to help you. And what does "clean" mean to you? Where is the cleaning going on? Also be aware that correlation does not necessarily tell you where signals are aligned the best, though it may be. It merely tells you what the sum of the products is. You could easily think of a signal where the max correlation is not where the best alignment of waveform shapes is. You might think of other metrics like min of a moving SAD or other such pattern recognition methods.

[Antonio Morales]

Thank you for your answer.

You can see attached an S1 and S2 signals example.

xcorr actually gives me what visually I would expect it to be (both are acceleration signals of the same event: a jump from an athlete).

[C22, lag22] = xcorr(S1, S2);
[M22,I22] = max(C22);
t22 = lag22(I22);
figure(1), plot(1:length(S1), S1, 'b', 1+t22:length(S2)+t22, S2, 'r'), title('S1 and S2 "Synch"')

After finding out the lag between both signals, I want to make them the same length by cutting the longest for further processing (that is what I meant by "clean").

This may be a very simple step, but I'm stuck. In the multiple signals I have, lengths of S1 and S2 are never the same, and the "lag" is sometimes negative and other positive.

How could I write an "if" condition that efficiently "cuts" or "eliminates" both signals edges, so that both S1 and S2 are aligned and the same length?

[Antonio Morales]

(Attachments just added in the comment above)

Answer 1

[Star Strider]

You can also use the alignsignals function. It is a recent introduction (I believe one of the R2015 releases). It give several options for the output.