%
% s671.m - MATLAB script in Section 6.7.1
%
% Filter specifications
%
Fs=8000;		% Sampling frequency 8 kHz
fc=800;		% Passband cutoff frequency 800 Hz
fs=1600;		% Stopband frequency 1.6 kHz
Rp=1;			% Passband ripple in dB
Rs=20;		% Stopband attenuation in dB
Wp=2*fc/Fs;	% Normalized passband edge frequency
Ws=2*fs/Fs;	% Normalized stopband edge frequency

%
% Filter design
&
[N,Wn]=buttord(Wp,Ws,Rp,Rs);	% Filter order selection
[b,a]=butter(N,Wn);		% Butterworth filter design
[Z,P,K]=tf2zp(b,a);		% Transfer function to zero-pole
[sos,G]=zp2sos(Z,P,K);		% Zero-pole to 2nd-order section