Butterworth filter

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

Answer 1

[Honglei Chen]

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

[federico valenti]

so than i filter this way?

matrix_filtered=filter(B,A,matrixToFilter);

[Honglei Chen]

Yes. Note that filter works on columns of matrixToFilter. You can find more details if you type

>> doc filter

[federico valenti]

Thanks a lot