%  ex_06_03_3.m :  習題 6.3
clear;

fp=[300 400];
fs=[200 500];
rp=3;
rs=40;
Fs=2000;
wp=2*fp/Fs;ws=2*fs/Fs;
[n,wn]=buttord(wp,ws,rp,rs);
[b,a]=butter(n,wp)
[h,w]=freqz(b,a,256,Fs);
h=20*log10(abs(h));
subplot(211);plot(w,h);grid;