MATLAB: Filtfilt and filter order

filtfilt filter order butterworth

I use a butterworth filter with the filtfilt function. How does the reverse filtering affect the total filter order? If I use a second order butterworth, does the filtfilt function act like a fourth order butterworth (without the shift) or has the reverse filtering no effect on the total filter order? Thnaks for your advice.

Best Answer

As I understand the filtfilt documentation, the effect is to produce a result (filtered signal) of a filter of double the order of the filter you give it. It has no effect on the filter itself. (The advantage if filtfilt is that it is phase-neutral.) So at least as I read the documentation, it would act as if your filter was a fourth-order filter in your example.

Related Solutions

MATLAB: Using zero-pole-gain Butterworth filter

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.

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

Déjà vu

how to design IIR highpass filter with cutoff frequency of 20Hz and FIR bandpass filter with cutoff frequency of 10Hz and 15Hz?

Make the appropriate changes to get the cascaded filter you want.

Best Answer

Related Solutions

MATLAB: Using zero-pole-gain Butterworth filter

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

Related Question