MATLAB: Using zero-pole-gain Butterworth filter

butterworth

Hi,
I want use Butterworth filter but this design:
% Zero-Pole-Gain design
[z,p,k] = butter(n,Wn,ftype);
How can I then filter data? For example, something like this:
dataOut = filter(b,a,dataIn);

Best Answer

The zero-pole-gain is a good start. To filter your data, I would convert it to second order section implementation for stability, then use that to filter your data. Use the filtfilt function to do the actual filtering, since it has a maximally flat phase response and so does not produce any phase distortion in your filtered signal.
It is always good to be certain your filter is doing what you want by using the freqz function first.
Try this:
[z,p,k] = butter(n,Wn,ftype);
[sos, g] = zp2sos(z, p, k);
figure(1)
freqz(sos, 2^16)
dataOut = filtfilt(sos, g, dataIn);
That should work.
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