# How to align multiple signals?

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Susan on 7 Feb 2023
Hi Matlab experts,
I'm trying to align these signals but have yet to be successful.
The signals are attached. They are periodic, noisy sin signals. I used the alignsignals function as well as xcorr to align the signals. Could somebody help me out with that?
Moreover, how can I compute the frequency of these signals?

Sulaymon Eshkabilov on 8 Feb 2023
Here is one of the viable solutions to compute resonant frequencies of each signal and find out if their are coherent:
fs = 1024;
S = [S1; S2; S3; S4; S5; S6];
N = length(S1);
freq = fs*(0:(N/2))/N; % Freq values
for ii=1:6
Y = fft(S(ii,:), N); % FFT of the signal s(t)
Yp = abs(Y/N); % Absolute value or magnitude of the signal spectrum
semilogy(freq,Yp(1:N/2+1), 'linewidth', 2)
hold all
end
title('FFT analysis of a signal')
xlabel('Frequency, [Hz]')
ylabel('Magnitude of signal = |S(f)|')
ylim([0, 0.025])
legend({'s1', 's2', 's3', 's4', 's5', 's6'})
grid on
You can check signal coherences using wcoherence() function:
wcoherence(S1,S2)
wcoherence(S2,S3)
wcoherence(S3,S4)
wcoherence(S4,S5)
wcoherence(S5,S6)
It looks like signal s5 and s6 are pure noise.
##### 2 CommentsShowHide 1 older comment
Sulaymon Eshkabilov on 8 Feb 2023
Edited: Sulaymon Eshkabilov on 8 Feb 2023
Most welcome. What do mean to align the signals in the time domain? Put them together or what? to make their peak values correspond?
You can try alignsignals() fcn:
[S2a, S3a] = alignsignals(S2, S3, [], "truncate");
nexttile
plot(S2), hold on
plot(S3)
nexttile
plot(S2a), hold on
plot(S3a)
hold off
See - DOC.

Sulaymon Eshkabilov on 7 Feb 2023
One fundamental question for signal processing is a "must", that is "what is the data sampling time or sampling frequency?"
Pl., provide this info.
Susan on 7 Feb 2023
Edited: Susan on 7 Feb 2023
@Sulaymon Eshkabilov Thanks for your response. The sampling rate of all signals equals 1024.

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