MATLAB: Bandpass filter

band pass filter

I want to run a signal through bandpass filter, but the data is sent one by one.
    t=0:0.0000001:1;
    a=sin(2*pi*250*t)+sin(2*pi*500*t);
    wn=[(240*0.00000001/2) (260*0.00000001/2)];
    [B,A]=butter(2,wn,'bandpass');
    for ii=0:length(t)
    z(ii)=filter(B,A,a(ii));
    end
I'm getting wrong data from the filter. What is wrong with the code??

Best Answer

The wn contain very low frequencies. Is this really wanted?
You cannot filter scalars. Try to omit the loop:
z = filter(B,A,a);
If you really have a good reason to filter the data element by element, you have to consider the current status of the filter:
s = [];
z = zeros(1, length(t));  % pre-allocate!
for ii = 1:length(t)      % Not 0:length(t) !
  [z(ii), s] = filter(B, A, a(ii), s);
end
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