A]=cheby1(Nc,rp,wn,'s');[num2,den2]=bilinear(B,A,fs);[h2,w]=freqz(num2,den2);[Ne,wn]=ellipord(w1,w2,rp,rs,'s')%椭圆型[B,A]=ellip(Ne,rp,rs,wn,'low','s');[num3,den3]=bilinear(B,A,fs);[h3,w]=freqz(num3,den3);f=w/(2*pi)*fs;plot(f,20*log10(abs(h1)),'-',f,20*log10(abs(h2)),'--',f,20*log10(abs(h3)),':');axis([0,4000,-100,10]);grid;xlabel('FrequencyinHz');ylabel('GainindB');title('三种数字低通滤波器');legend('巴特沃思数字低通滤波器','切比雪夫数字低通滤波器','椭圆数字低通滤波器',3);巴特沃思数字低通滤波器的系统函数系数:num1=0.0032?0.0129?0.0302?0.0453?0.0453?0.0302?0.0129?0.0032?0.0003den1=-2.7996?4.4581?-4.5412?3.2404?-1.6330?0.5780?-0.1370?0.0197?-0.0013切比雪夫数字低通滤波器的系统函数系数:num2=0.0026?0.0132?0.0264?0.0264?0.0132?0.0026den2=1-2.9775?4.2932?-3.5124?1.6145?-0.3334椭圆数字低通滤波器的系统函数系数:num3=0.03887?0.0363?0.0665?0.0363?0.0389den3=1?-2.1444?2.3658?-1.3250?0.3332程序结果图:
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