% first order of IIR notch filter
% Use bilinear meathod

clear;
Gb2=0.5;N=64;
[xn,fs,bits]=wavread('shutdown.wav');
xn=xn(:,1)';
subplot(411);plot(xn);
XZ=abs(fft(xn,N));
subplot(412);plot(XZ);grid;
[Xmax,xp]=max(XZ);
fmain=xp*fs/N;
clear Xmax xp XZ;
fc=1000;
w0=2*pi*fc/fs;
deltaw=0.1*pi;
b=1/(1+tan(deltaw/2)*(sqrt(1-Gb2)/sqrt(Gb2)));
B=[1 -2*cos(w0) 1].*b;
A=[1 -2*b*cos(w0) (2*b-1)];
yn=filter(B,A,xn);
subplot(413);plot(yn);
YZ=abs(fft(xn,N));subplot(414);plot(YZ);grid;
%subplot(412);w=0:pi/500:pi;H=freqz(B,A,w);plot(w/pi,abs(H));grid;
sound(yn,fs,bits)
pause;
sound(xn,fs,bits)