function [b,a]=afd_butt(Omegap,Omegar,Ap,Ar);
if Omegap<=0
    error('通帶邊緣必須大于0')
end
if (Omegar<=Omegap)
    error('阻帶邊緣必須大于通帶邊緣必須')
end
N=ceil((log10((10^(0.1*Ar)-1)/(10^(0.1*Ap)-1)))/(2*log10(Omegar/Omegap)));
fprintf('\n***巴特沃斯模擬低通濾波器階數=%2.0f\n',N);
OmegaC=Omegap/((10^(0.1*Ap)-1)^(1/(2*N)));
[b,a]=u_buttap(N,OmegaC);