[FieldTrip] Filter settings (Fieldtrip vs Brainvision

[Stephen Politzer-Ahles]

Mark,

I don't have an answer to your problem, but I have noticed a similar issue
with data from Neuroscan (like your data, mine seems more attenuated by the
Fieldtrip filter than the Neuroscan one; here is a comparison using a 30Hz
low-pass in Fieldtrip with the default options, versus 30Hz in Neuroscan
with zero phase shift and 12 dB/oct:
http://img685.imageshack.us/img685/5717/fieldtrippreprocessing.png). I'd
also be interested to hear if anyone on the list knows about what filter
settings to adjust to replicate those settings.

Best,
Steve Politzer-Ahles


> Message: 5
> Date: Fri, 23 Sep 2011 18:09:18 +0200
> From: Mark Noordenbos <mark.noordenbos at gmail.com>
> To: fieldtrip at donders.ru.nl
> Subject: [FieldTrip] Filter settings (Fieldtrip vs Brainvision
>        Analyzer)
> Message-ID:
>        <CAJSb8nOKezCwZKLay6PjHKGf7tHzfVCgsEDjtxWgYvWNf7NY1Q at mail.gmail.com
> >
> Content-Type: text/plain; charset="iso-8859-1"
>
> Dear all,
>
> I analyzed some data using Brainvision Analyzer and would like to
> re-analyze
> the same data using Fieldtrip. However, the final results are a bit
> different between Brainvision Analyzer and Fieldtrip.
> The main difference is because of differences in filtering of the data
> (without filtering the data is exactly the same). The filter in Fieldtrip
> seems to be much 'stricter' and as a consequence the amplitude is almost
> halved in the grandaverage!
>
> In Brainvision Analyzer I used the following filter setting:
>
> Butterworth Zero Phase Filters
> Low Cutoff: 1.0000 Hz, Time constant 0.1592s, 24 dB/oct
> High Cutoff: 30.0000 Hz, 24 dB/oct
> Notch Filter: ---
>
> In Fieldtrip I used the following filter settings
>
> cfg.lpfilter                = 'yes';
> cfg.hpfilter                = 'yes';
> cfg.lpfreq                  = 30;
> cfg.hpfreq                  = 1;
>
> cfg.lpfiltord = 6;
> cfg.hpfiltord = 6;
>
> cfg.lpfiltdir     = 'twopass';
> cfg.hpfiltdir     = 'twopass';
>
> Any suggestions for the Fieldtrip filter settings to resemble the
> Brainvision Analyzer filter settings as much as possible?
>
> Best,
> Mark
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-- 
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://www.linguistics.ku.edu/
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