ms15r24.m

《数字信号处理实验(MATLAB版)》这

fm=1;N=6;rp=1;as=20;
Wp=2*pi*fm;
dw=(2*Wp)/399;
w=0:dw:2*Wp;
h0=[ones(1,201),zeros(1,199)];
%设计巴特沃斯低通滤波器
[b,a]=butter(N,Wp,'s');
h=freqs(b,a,w);
subplot(3,1,1),plot(w/(2*pi),abs(h),'k',w/(2*pi),abs(h0));grid
axis([0 max(2*fm) 1.1*min(abs(h)) 1.1*max(abs(h))]);
%设计契比雪夫Ⅰ型低通滤波器
[b,a]=cheby1(N,rp,Wp,'s');
h=freqs(b,a,w);
subplot(3,1,2),plot(w/(2*pi),abs(h),'k',w/(2*pi),abs(h0));grid
axis([0 max(2*fm) 1.1*min(abs(h)) 1.1*max(abs(h))]);
%设计契比雪夫Ⅱ型低通滤波器
[b,a]=cheby2(N,as,Wp,'s');
h=freqs(b,a,w);
subplot(3,1,3),plot(w/(2*pi),abs(h),'k',w/(2*pi),abs(h0));grid
axis([0 max(2*fm) 1.1*min(abs(h)) 1.1*max(abs(h))]);