# How to align multiple signals?

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Susan 2023 年 2 月 7 日

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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### 採用された回答

Sulaymon Eshkabilov 2023 年 2 月 8 日
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 2023 年 2 月 8 日

@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 2023 年 2 月 8 日

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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### その他の回答 (1 件)

Sulaymon Eshkabilov 2023 年 2 月 7 日
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 2023 年 2 月 7 日

@Sulaymon Eshkabilov Thanks for your response. The sampling rate of all signals equals 1024.

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