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user3620862 February 2016

Adding signals and separate them using MATLAB

I have two signals m(t) = exp(-100*abs(t)) and c(t) = cos(2*pi*1000*t). I need to add them and then separate them using only a low pass filter (LPF) and a band pass filter (BPF) and plot the figures.

I wrote the code :

fs = 100*1000;
ts = 1/fs;
t = -0.1:ts:0.1-ts;
No = length(t);

m = exp(-100*abs(t));
c = cos(2*pi*1000*t);
g = m + c;

y = abs(g);

cutoff = 200;
[a b]= butter(5,2*cutoff*ts);

z = filter(a,b,y);

legend('Input Signal','Output Signal')
title('Case Study')

Note that I used LPF [a b] = butter(5,2*cutoff*ts);

The problem is that the plot is shifted up and I think this is because of the DC component. Can you help me to edit the code and fix the shift? And should I use BPF? If yes, how?


Noel Segura February 2016

The offset you are getting is from using the abs value of g. If instead of filtering y you filter g then you get a better result. The offset comes from the dc component of abs(c) since this is not centered over zero, and any low pass filter will maintain this offset

Alessiox February 2016

In the plot command, subtract the mean value, like this


Hope this is what you're looking for

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Asked in February 2016
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