# How to align multiple signals?

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Susan il 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?
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### Risposta accettata

Sulaymon Eshkabilov il 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.
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Susan il 8 Feb 2023
Modificato: Susan il 8 Feb 2023
@Sulaymon Eshkabilov Thank you so much for your response. I genuinely appreciate it.
Please tell me how I interpret the first figure's results regarding the relationship between the time domain signals.
I went through the wcoherence documentation but am still trying to figure out how to interpret the results. Any help on that would be greatly appreciated.
Finally, how should I do that if I want to align these signals in the time domain?
Sulaymon Eshkabilov il 8 Feb 2023
Modificato: Sulaymon Eshkabilov il 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.

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### Più risposte (1)

Sulaymon Eshkabilov il 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.
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Susan il 7 Feb 2023
Modificato: Susan il 7 Feb 2023
@Sulaymon Eshkabilov Thanks for your response. The sampling rate of all signals equals 1024.

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