supress high amplitude signal and only keep low amplitude

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

[Wayne King]

Are these waves oscillating at the same rate (frequency) or different frequencies?

[Juan Camilo Medina]

if both had the same frequency, then they will appear as the same wave with amplitude equal to the sum of the other two waves, and it would be indistinguishable.

[Wayne King]

Not necessarily

   t = 0:0.001:1-0.001;
   x = 2*cos(2*pi*100*t).*(t<=0.5);
   y = 1/4*sin(2*pi*100*t-pi/8);
   z = x+y;
   plot(t,z)

[Youssef Khmou]

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]

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')

Answer 1

[Juan Camilo Medina]

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