How to insert noise in a signal using matlab?
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Nur Fauzira Saidin
on 5 Nov 2015
Commented: Star Strider
on 5 Nov 2015
Hi. I want to create a signal with noise. I found this coding but I don't know how it works. Can somebody explain this to me?
x= cos(2*pi*12*[0:0.001:1.23]);
x(end) = [];
[b a] = butter(2,[0.6 0.7],'bandpass');
filtered_noise = filter(b,a,randn(1, length(x)*2));
x = (x + 0.5*filtered_noise(500:500+length(x)-1))/length(x)*2;
This is the result when I plot the x.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/151424/image.png)
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Star Strider
on 5 Nov 2015
It creates a signal in ‘x’, then creates band-limited noise by bandpass-filtering a Gaussian random vector (created by the randn call), the same length as ‘x’, and stores it in the ‘filtered_noise’ variable. It then adds that to the original ‘x’ and scales it to create the final value of ‘x’. (There is a bit more involved in the code than I described, but that is the essence of it.)
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Star Strider
on 5 Nov 2015
That appears to be correct.
If you want the frequency in Hz (again assuming the time unit is seconds), multiply the normalised frequency by Fn, or 500 Hz.
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