[Eeglablist] 0.01 Hz highpass filter isn't running

[Makoto Miyakoshi]

Hi Metin,

   1. EEGLAB's default filter function was changed when the version was 13.
   If you are using version 13 or older, update the EEGLAB. It solves the
   problem. In the older versions, EEGLAB's default behavior for determining
   the filter order for a high pass filter had a problem of
   choosing excessively steep slopes with correspondingly long filter order.
   It used to take hours to finish applying a high-pass filter.
   2. To apply a 0.01 Hz high-pass filter (FIR), I think the filter order
   will be something like 330-s long. This is probably inappropriate. An FIR
   filter is basically like a sliding window. Imagine you use a 330-s long
   sliding window process such as moving window average. It sounds too
   long, right?
   3. If you do not know the difference between passband edge and cutoff
   frequency, read https://urldefense.com/v3/__https://eeglab.org/others/Firfilt_FAQ__;!!Mih3wA!CVpCwc6bEYjHOC1TIvASx27q7We22-d0usbkMh1-GfqNEF9iNUoB40pjbRjb-Z0LSGvbjs-F748JrxUGDWmwx-vpLCY$ . Andreas Widmann
   practically wrote this page (i.e. I quoted him a lot). He also changed the
   default behavior of EEGLAB's filter, particularly the high-pass filter.

Makoto

On Wed, Feb 7, 2024 at 3:09 PM Metin Özyağcılar via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Dear EEGLAB community,
>
> I have recently tried to change the settings for my highpass filter that I
> used to pre-process my data. I was using a 0.05Hz highpass filter, now
> trying out 0.01 Hz, and I am using the function pop_eegfiltnew(). However,
> when I tried to run the function, even after 10-20minutes I see no
> progress.
>
> After doing some research and reading the manuals online, I’ve seen a
> recommendation that for FIR filters a lower limit of about 0.1 is
> recommendable and limits lower than that are not. I’ve additionally learned
> that the lower and higher limits used in this function do not directly
> correspond to the “cut-off” (e.g using 0.05, the “cut-off frequency” is set
> to 0.025). All of these led me to have some questions:
>
> 1) Is there any way to still run 0.01 highpass filter with pop_eegfiltnew()
> and if so how?
> 2) If I chose to run a 0.05 Hz highpass filter instead, would it be
> appropriate to still set the lower limit as 0.05 but also report the
> outcome of the function when writing the paper (i.e. transition band width:
> 0.05 Hz / passband edge(s): 0.05 Hz / cutoff frequency(ies) (-6 dB): 0.025
> Hz / filtering the data; zero-phase, non-causal)? I feel not so confident
> playing around with the parameters and the default settings of the
> function.
> 3) On an unrelated note: the filters are run very slow, even the 0.05Hz.
> Does anyone else maybe have the same issue and if so how are you dealing
> with it? I updated MATLAB, EEGLAB, even my operating system to the latest
> version + freed up my storge but nothing has changed.
>
> Any feedback would be highly appreciated. Thank you!
>
> Best,
> Metin
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