[Eeglablist] Filtering trouble

[Erin McMullen Jonaitis]

Greetings, all,

I am trying to filter a set of 128-channel EEG data and am not sure
that the filter tool is working correctly -- and I'm not sure how I
can tell.  I read that using a bandpass filter is unpredictable in
EEGLab, so I started with a lowpass filter and then moved onto the
highpass, checking the spectral content of the data before and after
each filter.  However, my spectrum diagram winds up looking not much
like the example diagram: rather than a few distinguishable lines
there are swaths of color.  I imagine this is due to the large number
of channels?  When I filter, the shapes of some of these swaths
change, but others show no change, leaving me confused about whether
the filter worked.  I have attached spectral plots taken before and
after the lowpass filter (threshold = 45 Hz) to illustrate the
problem.

Additionally, it seems I am unable to use 0.1 Hz as the lower edge of
my accepted band -- when I try to do the highpass step, I get the
following error:
Filter error: continuous data portion too narrow (DC removed if highpass only)
Processing continuous data (307201:450306)
eegfilt() - performing 7680-point highpass filtering.
eegfilt() - highpass transition band width is 0.01 Hz.

In case it matters: I am using EEGLab v. 6.01b on Matlab student
version 7.0.0.27 (Release 14), and my data were recorded using
Biosemi.

Thanks for any insight you can offer, and my apologies if this is a
common topic.

Erin McMullen Jonaitis
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