MATLAB: Having a problem using an iir notch filter

filteringiir notch

hello everyone,
i want to filter 50 Hz sinus and therefore i implemented a notch filter such as shown in the help. i don'w know why it doesn't work. does everyone have a clue ? see also the attached file 'debuging' this is the program :
if true
  % code
end
*t=0:0.0005:0.5; % fs=2000Hz
x=sin(2*pi*50*t)+sin(2*pi*70*t);
figure;
plot(t,x);
title('Sum of sinuses - of 50Hz & of 70Hz ');
% implementation of the notch filter
wo = 50/(2000/2);  bw = wo/35;
[b,a] = iirnotch(wo,bw);
fvtool(b,a);
%signal after filterization
figure;
g=filter(b,a,x);
plot(t,g);
title('The signal after removing its 50 Hz sinus');
%figure of 70 Hz for comarison to what i need to get
figure;
y=sin(2*pi*70*t);
plot(t,y);
title('A 70 Hz sinus - for comparison');*
thanks a lot

Best Answer

Kobi, did you also supply the optional Ab input argument as I did?
nyquist = 2000/2;
 w0 = 50/nyquist;
 bw = w0/20;
 [b,a] = iirnotch(w0,bw,20);
 y = filtfilt(b,a,x);
 plot(t,y);
From your output it does not appear that you did.
If you execute the above, you should see that is pretty much a clean 70-Hz sinewave with a reduction in amplitude.
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