[Eeglablist] Lowpass filtering after preprocessing

Andreas Widmann widmann at uni-leipzig.de
Wed Mar 1 05:09:36 PST 2017


Hi Eric,

> I have an additional question: Does it matter when you perform resampling? Can it be done both before and after filtering? I've been doing it after filtering and it seems to work well.
These are all linear operations, so it actually shouldn’t matter (if done before epoching as also resampling implies filtering; IIRC there were also other problems with resampling of epoched data but I do not remember the details).

Best,
Andreas

> Best,
> 
> Eric
> 
> On Tue, Feb 28, 2017 at 2:52 PM, Andreas Widmann <widmann at uni-leipzig.de> wrote:
> Hi Eric,
> 
> > Would it be better if I remove the epochs and go "back" to continous data and then filter and epoch again? Or doesn't that make any difference?
> Not sure what you mean by ""back" to continous data“. You mean just concatenating the epochs? This would make things worse. Or filtering the original really continuous data? This should make the difference.
> 
> Would it be ok to keep the discussion on list? Best,
> Andreas
> 
> >
> > Best,
> >
> > Eric
> >
> > On Tue, Feb 28, 2017 at 11:14 AM, Andreas Widmann <widmann at uni-leipzig.de> wrote:
> > Hi Eric,
> >
> > I recommend not to filter epoched data unless absolutely necessary. Any filter implementation has to extrapolate the signal at the (epoch) edges the one or the other way possibly introducing edge effects depending on the signal and extrapolation algorithm (possibly also affecting phase). Edge effects are indeed usually less pronounced and problematic for lowpass filters than for highpass filters but cannot be excluded in general.
> >
> > Hope this helps! Best,
> > Andreas
> >
> > > Am 27.02.2017 um 18:18 schrieb Eric HG <erichg2013 at gmail.com>:
> > >
> > > Hi everyone,
> > >
> > > Is there any problem to perform lowpass filtering after preprocessing when preprocessing includes the following:
> > > High- and low-pass filtering, cleanline, epoching, removal of epochs, average referencing and ICA?
> > >
> > > Thanks a lot,
> > >
> > > Eric
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> 
> 



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