[Eeglablist] Phase Shift when using EEGLAB Filters

[Makoto Miyakoshi]

Dear Marco,

It shifts, but subsequently shifts back, so no problem.

In these shifting, as the bottom plot in your picture shows, phase shifts
linearly as frequency shifts, which assures no distortion in the temporal
domain. This means that that, for example, if your 10 Hz shifts 180
degrees, which is 50 ms, then your 100 (=10*10) Hz shifts 1800 (=180*10)
degrees, which is also 50 ms.

Makoto


2013/2/21 Marco Montalto <montaltomarco at onvol.net>

> Dear List,
>
> I have a question to ask regarding filters in EEGLAB. I am using Basic FIR
> Filter (new) to bandpass filter my data between 0.5 - 30 Hz. I have read in
> previous posts that all EEGLAB filters are zero-phase filters. Yet the
> resulting Frequency Response Plot shows that there is a phase shift in the
> passband. Here is a link to the saved image of the Frequency Response Plot:
>
> https://www.dropbox.com/s/uwruvr05np9qxq7/untitled.jpg
>
> Would anyone know why this is so i.e. why there is this phase shift? And
> also ways to overcome this phase shift?
>
> Thanks and looking forward to hearing from you.
>
> Regards,
> Marco Montalto
>
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-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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