Butterworth filter frequency response with 2nd order, 3rd order and 4th order figures

hi,

i want butterworth filter frequency response with 2nd order, 3rd order and 4th order in a single plot..

Answer 1

[Honglei Chen]

Just as an example

[b1,a1] = butter(2,0.5);
[b2,a2] = butter(3,0.5);
fvtool(b1,a1,b2,a2)