[Eeglablist] Phase Shift when using EEGLAB Filters

[Marco Montalto]

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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