supress high amplitude signal and only keep low amplitude

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i have a continuous positive signal which has a wave of high amplitude followed by a low aplitude i want to supress the high amplitude wave completely and only keep low amplitude signal
  5 Comments
Youssef  Khmou
Youssef Khmou on 5 Mar 2013
Edited: Youssef Khmou on 5 Mar 2013
hi,@Wayne and @Juan : the Amplitudes are Completely added only if the signals have the same Frequency and same phase .
I reproduce Wayne s example ( modified ) :
t = 0:0.001:1-0.001;
x = 2*cos(2*pi*100*t);
y = 4*cos(2*pi*100*t-pi/8);
z = x+y;
plot(t,z)
x and y have the same Freq, but y contains a delay phase (pi/8) then Max(Z)=5.69 not 6 v .
Juan Camilo Medina
Juan Camilo Medina on 5 Mar 2013
Edited: Juan Camilo Medina on 5 Mar 2013
OK, if the phases are different, the result is not exactly the same wave with amplitude equal to the sum of the other two waves. But still, the result is a "single" wave with the same frequency but shifted and different amplitude. If that is what you have, try a Fourier type sine-cosine basis functions decomposition:
t = 0:0.001:1-0.001;
a=5; phi=-1/8; f=10;
x = a*sin(2*pi*f*t+phi); % origial"mixed" wave
figure(1); clf; plot(t,x); hold on;
% decomposition into fourier basis functions
y = (a*sin(pi/2+phi))*sin(2*pi*f*t);
z = (a*sin(phi))*cos(2*pi*f*t);
plot(t,y+z,'--r')

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Accepted Answer

Juan Camilo Medina
Juan Camilo Medina on 5 Mar 2013
If they oscillate at different frequencies, you can create a high-pass filter, just read the help for the functions
[B,A] = butter(N,Wn,'high'); % this is just one of many filters types
Y = filter(B,A,X); % where X is your signal

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