[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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