There is not really much difference. It is necessary to get the matching frequency vector (‘wh’ and ‘wc’ here) from the freqs function, then plot the magnitudes and phases as functions of them, respectively:
Wn = [2000 2500];
[b,a] = butter(4,Wn,'stop','s');
[h,wh] = freqs(b,a) ;
Wn = [2000 2500];
[d,e] = cheby1(4,3,Wn,'stop','s');
[c,wc] = freqs(d,e) ;
mag = mag2db(abs(h));
phase1 = angle(h);
phasedeg1 = phase1*180/pi;
subplot(2,1,1), semilogx(wh,mag), grid on
xlabel 'Frequency (rad/s)', ylabel Magnitude
xlim([2000 3000])
hold on
subplot(2,1,2), semilogx(wh,phasedeg1), grid on
xlabel 'Frequency (rad/s)', ylabel 'Phase (degrees)'
xlim([2000 3000])
hold on
bag = mag2db(abs(c));
phase2 = angle(c);
phasedeg2 = phase2*180/pi;
subplot(2,1,1), semilogx(wc,bag), grid on
xlabel 'Frequency (rad/s)', ylabel Magnitude
hold on
subplot(2,1,2), semilogx(wc,phasedeg2), grid on
xlabel 'Frequency (rad/s)', ylabel 'Phase (degrees)'
xlim([2000 3000])
They results are quite close, considering that the filters themselves are much different.
