%  ex_07_12_1.m :  習題 7.12


clear all;
clc;
N = 1000;
Fs = 1000;
b = [1, 0, 0,0,0,0,-3,0,0,0,0,0,3,0,0,0,0,0,-1];
a = [1, -3 ,3, -1];
[H,w] = freqz(b,a,N,Fs);
h = impz(b,a,19);
Hr = abs(H);
Hr=Hr/216;
Hr = 20*log10(Hr);
Hp = angle(H);
Hp = unwrap(Hp);
subplot(221);plot(w,Hr);
subplot(222);plot(w,Hp);