clc,clear all,close all;
ws1=0.15*pi;           %給定各邊界頻率
wp1=0.3*pi;
wp2=0.5*pi;
ws2=0.65*pi;
As=40;                 %As為阻帶最小衰減
tr_width=min((wp1-ws1),(ws2-wp2));           %過渡帶，兩個過渡帶應該相等
M=(As-7.95)/(2.285*tr_width)+1;              %濾波器長度M
beta=0.5842*(As-21)^0.4+0.07886*(As-21);     %求出beta值
w_kai=(kaiser(M,beta))';                     %給出凱澤窗
n=[0:1:M];
wc1=(ws1+wp1)/2;                             %兩個截止頻率
wc2=(ws2+wp2)/2;
hd=ideal_lp(wc2,M+1)-ideal_lp(wc1,M+1);      %ideal_lp函數用來生成低通濾波器單位沖擊響應，兩個低通想減得到帶通
h=hd.*w_kai;                                 %單位沖擊與凱澤窗相乘
[db,mag,pha,grd,w]=freqz_m(h,[1]);           %產生絕對值的幅度響應和DB的響應
%依次作出理想脈沖響應，凱澤窗，實際沖擊響應和最終的DB響應
subplot(2,2,1);
stem(n,hd);
title('ideal impulse response');
xlabel('n');ylabel('hd(n)');
subplot(2,2,2);
stem(n,w_kai);
title('kaiser window');
xlabel('n');ylabel('kaiser(n)');
subplot(2,2,3);
stem(n,h);
title('actual impulse response');
xlabel('n');ylabel('h(n)');
subplot(2,2,4);
plot(w/pi,db);
title('magnitude response in db');
grid;
xlabel('frequency in pi units');
ylabel('Decibels');