MATLAB: Butterworth filter

butterworthfilterfilter design

Hi! I need a butterworth filter 4th order with 0.1Hz and 25Hz frequencies for 200 Hz sample rate function
i typed: rate =200;
f1=0.1;
f2=25;
order=2; % in the butter specific it says If Wn is a two-element vector, Wn = [W1 W2], BUTTER returns an order 2N %bandpass filter with passband W1 < W < W2.
B = butter(order,[f1/(rate/2) f2/(rate/2)]);
is it correct? How can i draw the butterworth's graph? with plot(B)?
TY sooooooooo much

Best Answer

Hi Federico,
Butterworth filter is an IIR filter, so you will need to get the denominator too, i.e., using the syntax
[B,A] = butter(order,[f1/(rate/2) f2/(rate/2)]);
There are several ways you can visualize the response. I would recommend to use fvtool, e.g.,
fvtool(B,A)
You can also do
freqz(B,A)
if you want.
HTH,
Honglei
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