窗函式設計低通濾波器：

fp=1000;

fc=1200;

as=100;

ap=1;

fs=22000;

wp=2*fp/fs;

wc=2*fc/fs;

N=ceil((as-7.95)/(14.36*(wc-wp)/2))+1;

beta=0.1102*(as-8.7);

window=Kaiser(N+1,beta);

b=fir1(N,wc,window);

freqz(b,1,512,fs);

高通濾波器：

fs=22000;

Wp=2*5000/fs;

Ws=2*4800/fs;

Ap=1;

As=100;

N=ceil(8*pi/(Wp-Ws))+1;

N=N+mod(N+1,2)+1;

Wc=(Wp+Ws)/2/pi;

h=fir1(N,Wc,"high");

omega=linspace(0,pi,512);

freqz(h,1,omega);

帶通濾波器：

fs=22000;

Wp1=2*1200/fs;

Wp2=2*3000/fs;

Wc1=2*1000/fs;

Wc2=2*3200/fs;

Ap=1;

As=100;

W1=(Wp1+Wc1)/2;

W2=(Wp2+Wc2)/2;

wdth=min((Wp1-Wc1),(Wc2-Wp2));

N=ceil(11*pi/wdth)+1;

b = fir1(N,[W1 W2]);

freqz(b,1,512,fs)

雙線性法設計低通濾波器：

fp=1000;

fc=1200;

as=100;

ap=1;

fs=22000;

wp=2*fp/fs;

wc=2*fc/fs; %歸一化截止頻率

[n,wn]=ellipord(wp,wc,ap,as);%求數字濾波器的最小階數和歸一化截止頻率

[b,a]=ellip(n,ap,as,wn);%求傳遞函式的分子分母系數

freqz(b,a,512,fs);