[Mne_analysis] Designing IIR Filter with Steeper Attenuation

Sam Zorowitz szorowi1 at gmail.com
Sun Nov 22 17:16:11 EST 2015
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Dear MNE list,

Filtering-related question here. Using the mne-python default 4th-order BW
filter, I've noticed that even when lowpassing to 120 Hz, the cHPI
artifacts in my MEG data bleeds through substantially. This problem goes
away, however, if using FFT instead.

My group is worried that the FFT filter distorts the phase relationships
among/between the frequency bands in the MEG data. So two questions:

   1. Matti has said (in-person on Friday) that the FFT filter used in
   MNE-C will not disrupt phase relationships. Is this true of the FFT filter
   in mne-python/scipy?
   2. If the FFT filter might distort phase relationships, how can I design
   an IIR filter with a steeper attenuation using mne construct_iir_filter?

Best,
Sam
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