% Digital Filter Specifications:
wp=0.2*pi;       % digital Passband freq in rad
ws=0.3*pi;       % digital Stopband freq in rad
Rp=1;            % Passband ripple in dB
As=15;           % Stopband attenuation in dB
% Analog Prototype Specifications:Inverse mapping for frequencies
T=1;                     %       Set T=1
OmegaP=wp/T;             %       Prototype Passband freq
OmegaS=ws/T;             %       Prototype Stopband freq
% Analog Butterworth Prototype Filter Calculation:
[cs,ds]=afd_butt(OmegaP,OmegaS,Rp,As);
% ***Butterworth Filter Order=6
% Impulse Invariance transformation:
[b,a]=imp_invr(cs,ds,T);
[C,B,A]=dir2par(b,a)
[db,mag,pha,grd,w]=freqz_m(b,a);