[Eeglablist] filter problems
Arnaud Delorme
arno at salk.edu
Wed Dec 7 08:12:18 PST 2005
Dear Nathan,
> we've encountered some problems during filtering.
> Data: MEG (SR 678.17; .1-200 Hz); 10 times auditory stimulation
>
> In eeglab we filterd the raw data 1-20 Hz bandpass (eeglab 4.512 &
> 4.515 in Matlab 6.5 & Matlab 7.04). However when looking at the data
> we see simply a sinusoidal modulation at 22 Hz.
Yes, this is a known problem as described in the tutorial page you
mention. It does not always happen. It is directly linked to the Matlab
design filter function so there is little we can do about it. Low pass
then high pass your data (as you performed) usually solves this problem.
Andreas Widmann, who programmed the BVA import function, is thinking of
putting in a new improved linear filter plugin in the near future. You
also have the alternative of using the non-linear IIR filter plugin.
Best,
Arno
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