MATLAB: Butterworth passband filter transfer function in matlab

filterMATLABsignal processing

hello,

i am using the function butter as a butterworth passband filter but i need its transfer function order n

thanks in advance

Best Answer

The butter function returns the numerator polynomial ‘b’ and denominator polynomial ‘a’ of the transfer function as vectors if you request it:

[b,a] = butter(n,Wn,ftype)

See the documentation for details.

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MATLAB: Butterworth filter

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

MATLAB: Fir and iir filtering

You have to know your filter specifications. If you do, you can do both with fdesign.lowpass and fdesign.highpass

fdesign.lowpass and fdesign.highpass have different specification strings which support different filter designs.

The default string 'Fp,Fst,Ap,Ast' supports both FIR and IIR designs.

Here is an example:

Design a lowpass filter with a passband frequency of 1 kHz, a stopband frequency of 1.5 kHz, passband ripple of 0.5 dB, and stopband attenuation of 40 dB. The sampling frequency is 20 kHz

   d = fdesign.lowpass('Fp,Fst,Ap,Ast',1e3,1.5e3,0.5,40,20e3);
   designmethods(d)  %shows which designs are valid for this spec
   Hdeq = design(d,'equiripple'); % FIR filter
   Hbutt = design(d,'butter'); %IIR design

Best Answer

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MATLAB: Butterworth filter

MATLAB: Fir and iir filtering

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