[Eeglablist] filter order and antialiasing in EEGlab

[Andreas Widmann]

> Am 20.06.2017 um 13:12 schrieb Ahmad, Jumana <jumana.ahmad at kcl.ac.uk>:
> 
> Dear EEG lab.
> I am using EEGlab version eeglab13_6_5b
> I fitter sequentially, but I have actually done this in order of:
> High pass filter
> Low pass filter.
> I then down sample.
>  
> I have a few questions:
>  
> Does the order of high or low pass filtering matter? 
No, in general these are all linear operations and order should not matter. There might be small non-linearities at the signal edges/boundaries due to data padding, however, these should be minor and hardly noticeable with continuous regular EEG data. Note, that filtering will be considerably faster on the downsampled data.

> Does the EEGlab function include an antialiasing filter, so that if you do not low pass first, you are slightly protected from antialiasing?
Yes. But note that the (MATLAB default) anti-aliasing filter is suboptimal and was replaced in 2015 by a custom version (https://sccn.ucsd.edu/bugzilla/show_bug.cgi?id=1757). Not sure which EEGLAB version reflects the changes. You can check whether your EEGLAB version contains the changes from this commit:
https://bitbucket.org/sccn_eeglab/eeglab/diff/functions/popfunc/pop_resample.m?diff2=23c6aafa5dde&at=octavecompat

Hope this helps,
Andreas

> Best wishes,
> Jumana 
>  
> ------------------------------------------
> Jumana Ahmad
> Post-Doctoral Research Worker in Cognitive Neuroscience 
> EU-AIMS Longitudinal European Autism Project (LEAP) & SynaG Study
> Room M1.09. Department of Forensic and Neurodevelopmental Sciences (PO 23) | Institute of Psychiatry, Psychology & Neuroscience | King’s College London | 16 De Crespigny Park | London SE5 8AF
>  
> Phone: 0207848 0260| Email: jumana.ahmad at kcl.ac.uk | Website: www.eu-aims.eu | Facebook: www.facebook.com/euaims
>  
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