# Compare two signals of the same underlying process in order to create a noise reducing filter

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Adam Nooberson on 19 Apr 2020
Answered: Sai Sri Pathuri on 28 May 2020
I have two signals,1 & 2. Both are from the same underlying process, but measured with different equipment. Signal 1 has sampling frequency 1 Hz. Signal 2 has sampling frequency 0.2 Hz.
I want to compare the two signals in order to create a noise reducing filter for signal 1. Right now I do it the following way.
1. Interpolate signal 2.
2. Use pwelch and mscohere to look at the signal's similarities.
3. Design a lowpass filter since mscohere only gives a high value for low frequencies.
Fn = Fs/2;
Wp = Flp/Fn;
Ws = (Flp*0.8)/Fn;
[n,Wn] = buttord(Wp,Ws,Rp,Rs);
[z,p,k] = butter(n,Wn);
[sosbp,gbp] = zp2sos(z,p,k);
freqz(sosbp, 2^20, Fs)
filtered_signal = filtfilt(sosbp, gbp, signal);
I'm a total beginner at signal processing, what should I look at? How should I pick lowpass frequency, Ws, Rp, Rs?

Sai Sri Pathuri on 28 May 2020

R2018b

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