# How to add low frequency noise to the signal?

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632541 on 16 Sep 2021
Answered: Mathieu NOE on 16 Sep 2021
How to add low frequency noise (less than 3Hz) to signal in matlab?
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### Accepted Answer

Mathieu NOE on 16 Sep 2021
hello
this is a simple demo showing a sine signal corrupted by a low frequency noise . You can adjust the parameters to your own needs
Fs = 1000;
samples = 10000;
dt = 1/Fs;
t = (0:samples-1)*dt;
y = 3*sin(2*pi*1*t); % signal - adjust amplitude to your needs
noise = 1.5*randn(size(t)); % noise (before filtering) - adjust amplitude to your needs
% low pass filter : Butterworth filter
NN = 2; % filter order
fc = 3; % cut off frequency (Hz)
Wn = fc/(Fs/2); % normalized cut off frequency
[B,A] = butter(NN,Wn);
noise_filtered = filter(B,A,noise); % noise (after LP filtering)
y_noisy = y+noise_filtered; % signal + noise
figure(1)
plot(t,y,t,y_noisy);legend('signal','signal + noise');
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