%
%  notch1.m - Magnitude response of a notch filter
%             with both zeros and poles
%
w0=0.2*pi; th0=w0; r=0.85;	% Define constants

% Define the transfer function H(z)
b(1)=1; b(2)=-2*cos(w0); b(3)=1;
a(1)=1; a(2)=-2*r*cos(th0); a(3)=r*r;

% Calculate the magnitude response of H(z)
[h,w]=freqz(b,a,128); mag=20*log10(abs(h));

% Plot the magnitude response of H(z)
plot(w/pi/2,mag,'b-');
xlabel('Normalized frequency');
ylabel('Magnitude (dB)');
title('Magnitude response of transfer function H(z)');
grid;