function [b,a] = makenotch(Fs, W0, BandWidth) Fn = Fs/2; % Nyquist freq [Hz] w0 = W0*pi/Fn; % notch frequency normalized B = BandWidth*pi/Fn; % normalized bandwidth k1 = -cos(w0); k2 = (1 - tan(B/2))/(1 + tan(B/2)); b = [1+k2 2*k1*(1+k2) 1+k2]; a = [2 2*k1*(1+k2) 2*k2]; #figure(1); % look at the frequency response of your filter #freqz(b,a); # now filter(b,a,input)