iir_first_low_test.m

不是直接调用函数

% first order of IIR lowpass filter
% Use bilinear meathod

clear;
fc=1000;Gc2=0.5;N=2^15;
[xn,fs,bits]=wavread('shutdown.wav');
xn=xn(:,1)';
plot(abs(fft(xn,N)),'r');hold on;
wc=2*pi*fc/fs;
omegac=tan(wc/2);
alpha=(sqrt(Gc2)/sqrt(1-Gc2))*omegac;
a=(1-alpha)/(1+alpha);
b=(1+a)/2;
B=[b b];
A=[1 -a];
yn=filter(B,A,xn);
plot(abs(fft(yn,N)));
sound(yn,fs,bits);
%w=0:pi/300:pi;Hw2=alpha^2./(alpha^2+(tan(w/2)).^2);plot(w/pi,Hw2);grid;