How can I obtain the same filtered signal with the fonction filter and filtfilt (with only a phase interval)?

Usually, I use the fonction filtfilt ([b,a] = butter(2,2*10/200) ; datafilt=filtfilt(b,a,data);) and I would like obtain exactly the same filtered data with the fonction 'filter' (with the additional phase interval only). Do you know what are the corresponding parameters with the fonction filter to obtain that?

Thank you Jérémy

Answer 1

[Wayne King]

Because you are using an IIR filter that is going to be essentially impossible because there is no simple delay you can correct for. The group delay of your IIR filter will be frequency-dependent.

   [b,a] = butter(2,2*10/200);
   [gd,w] = grpdelay(b,a);
   plot(w,gd)

If you were using a linear-phase FIR filter, it is easy to compensate for the delay.