%圖3-1-1不同階次巴特沃思濾波器的幅頻特性
ord=3;
[b,a] = butter(ord,0.4);
[h,w]=freqz(b,a,512,1000);
hold on;							%數(shù)字濾波器頻響
habs=(abs(h));
plot(w,habs);

ord=6;
[b,a] = butter(ord,0.4);
[h,w]=freqz(b,a,512,1000);
hold on;							%數(shù)字濾波器頻響
habs=(abs(h));
plot(w,habs);

ord=10;
[b,a] = butter(ord,0.4);
[h,w]=freqz(b,a,512,1000);
hold on;							%數(shù)字濾波器頻響
habs=(abs(h));
plot(w,habs);