[FieldTrip] question about ft_preproc_bandpassfilter

Lara Todorova lara.todorova at gmail.com
Wed Jul 7 16:46:34 CEST 2021


Dear all,

I am applying a bandpass filter 8-12 Hz on EEG data, 64 channels, 1000
sampling frequency. The data was preprocessed in eeglab software.

I get an error that suggests changing the order of the filter
ft_error('Calculated filter coefficients have poles on or outside the unit
circle and will not be stable. Try a higher cutoff frequency or a different
type/order of filter.');

I'm not sure why I get this error. Does anyone have an idea?

Indeed when I change the filter order to 3 instead of default 4, the
problem is solved.
I also noticed that if I change Fs to 500 instead of 1000 it also works.

Could someone comment on how Fs affects filtering in
ft_preproc_bandpassfilter or what are the consequences of switching to the
filter of the lower order?

Thanks,
Lara

-- 
Lara Todorova | PhD
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