%  ex_06_03_1.m :  習題 6.3
clear all

fp=400;
fs=300;Fs=1000;
rp=3;
rs=35;
wp=2*fp/Fs; 
ws=2*fs/Fs;

[nz,wn]=buttord(wp,ws,rp,rs);
[bz,az]=butter(nz,wp,'high')
[h,w]=freqz(bz,az,128,Fs);
subplot(211)
plot(w,20*log10(abs(h)));grid;
ylabel(' High-pass DF')