[Eeglablist] Plugins and bandpass FIR filtering

Arnaud Delorme arno at salk.edu
Wed Apr 27 18:04:28 PDT 2005


Dear Brahim,

I realized the IIR eeglab plugin already uses filtfilt.
Matworks also recommend using it for IIR filters (see link below)

http://www.mathworks.com/access/helpdesk/help/toolbox/signal/filterd3.html

So the phase distortion I was mentioning does not apply in this case. It 
also means that IIR filtering may be recommended for filtering EEG data 
in most cases (since the signal drop-off is sharper).

Arno

Brahim HAMADICHAREF wrote:

> Hi all,
>
> I also experienced same problems with MATLAB SP2 (version 7.0.4)
> but have not managed to find out where the problems comes from.
>
> For the IIR filter design and phase problems ...
> Use MATLAB Signal Processing Toolbox with the function
> filtfilt for "Zero-phase digital filtering"
>
> "y = filtfilt(b,a,x) performs zero-phase digital filtering by processing
> the input data in both the forward and reverse directions. After 
> filtering
> in the forward direction, it reverses the filtered sequence and runs 
> it back
> through the filter. The resulting sequence has precisely zero-phase 
> distortion
> and double the filter order. filtfilt minimizes start-up and ending 
> transients
> by matching initial conditions, and works for both real and complex 
> inputs."
>
> Maybe the IIR filtering plugin could be modified to incorporate such 
> method.
>
> For the FIR filter design... you can use the function "firpm" which is 
> the
> Parks-McClellan optimal FIR filter design (also called remez) to first
> estimate the minimal order of the filter from your specs and then 
> calculate
> the coefficients. I have emailed Andreas an example and can give to 
> anyone
> by email request.
>
> Best regards
>
> Brahim HAMADICHAREF
> Signal Processing and Multimedia Communications research Group
> Plymouth, Devon, UK
> http://www.tech.plym.ac.uk/spmc/
>
>
>
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