% Chapter 8: Example 8.29
%            Elliptic Bandpass Filter Design:
%                Use of the ELLIP function
%
% Digital Filter Specifications:        % Type: Elliptic Bandpass
ws = [0.3*pi 0.75*pi];                  % Dig. stopband edge frequency
wp = [0.4*pi 0.6*pi];                   % Dig. passband edge frequency
Rp = 1;	                                % Passband ripple in dB
As = 40;                                % Stopband attenuation in dB
Ripple = 10 ^ (-Rp/20);                 % Passband ripple
Attn = 10 ^ (-As/20);                   % Passband attenuation

% Calculations of Elliptic Filter Parameters:
[N,wn] = ellipord(wp/pi,ws/pi,Rp,As);

% Digital Elliptic Bandpass Filter Design:
[b,a] = ellip(N,Rp,As,wn);

% Cascade Form Realization:
[b0,B,A] = dir2cas(b,a)
%%b0 = 0.0197
%%B = 1.0000    1.5066    1.0000
%%    1.0000    0.9268    1.0000
%%    1.0000   -0.9268    1.0000
%%    1.0000   -1.5066    1.0000
%%A = 1.0000    0.5963    0.9399
%%    1.0000    0.2774    0.7929
%%    1.0000   -0.2774    0.7929
%%    1.0000   -0.5963    0.9399

% Plotting:
figure(1); subplot(1,1,1)
[db,mag,pha,grd,w] = freqz_m(b,a);
subplot(2,2,1);plot(w/pi,mag);grid;title('Magnitude Response')
xlabel('frequency in pi units'); axis([0, 1, 0, 1])
set(gca,'XTickMode','manual','XTick',[0;0.3;0.4;0.6;0.75;1])
set(gca,'YTickMode','manual','YTick',[0,Ripple,1]);
subplot(2,2,3);plot(w/pi,db);grid;title('Magnitude in dB')
xlabel('frequency in pi units'); axis([0 1 -50 0]);
set(gca,'XTickMode','manual','XTick',[0;0.3;0.4;0.6;0.75;1])
set(gca,'YTickMode','manual','YTick',[-40;0])
set(gca,'YTickLabelMode','manual','YTickLabels',['40';' 0'])
subplot(2,2,2);plot(w/pi,pha/pi);grid;title('Phase Response')
xlabel('frequency in pi units');ylabel('phase in pi units') 
set(gca,'XTickMode','manual','XTick',[0;0.3;0.4;0.6;0.75;1])
subplot(2,2,4);plot(w/pi,grd);grid;title('Group Delay')
xlabel('frequency in pi units'); ylabel('samples')
set(gca,'XTickMode','manual','XTick',[0;0.3;0.4;0.6;0.75;1])