fs=20000;
wp=2*pi*2100/fs;
ws=2*pi*8000/fs;
Rp=0.5;
Rs=30;
Ts=1/fs;
Wp=2*Ts*tan(wp/2);Ws=2*Ts*tan(ws/2);
[N,Wn]=ellipord(Wp,Ws,Rp,Rs,'s');
[z,p,k]=ellipap(N,Rp,Rs);
[Bap,Aap]=zp2tf(z,p,k);
[b,a]=lp2lp(Bap,Aap,Wn);
[bz,az]=bilinear(b,a,fs);
[H,f]=freqz(bz,az,512,fs);
su
bp
lot(2,1,1);
plot(f,20*log(abs(H)));
title('N=2 频率响应');
grid on;
xlabel('频率/Hz');
ylabel('振幅/dB');
subplot(2,1,2);
plot(f,abs(H));grid on;
xlabel('频率/Hz');
ylabel('振幅/H')；

既然感激无止境，不如给50QB吧，聊表你的感激。