[Eeglablist] 50 Hz Removal

[Makoto Miyakoshi]

Dear Fabio,

> even though I band-pass filter 2-45 Hz, it does not remove the 50Hz.

Even if you set your cutoff frequency at 45 Hz, if the transition band
width is 20 Hz, it would not suppress 50 Hz very well! Check what EEGLAB
filter does--at 45 Hz, it specifies the pass-band edge. I don't know if it
guarantees maximum suppression at 50 Hz. Maybe you want to check your
filter parameters.
https://sccn.ucsd.edu/wiki/Firfilt_FAQ

To suppress line noise,

   1. Apply CleanLine. https://www.nitrc.org/projects/cleanline/
   2. If CleanLine does not work (see
   https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Remove_line_noise_using_CleanLine_.2805.2F17.2F2018_Updated.29),
   apply either notch filter at 50 Hz or low-pass filter before 50 Hz.

Makoto

On Wed, Dec 5, 2018 at 9:49 AM Fabio Castro <Fabio.Castro at brunel.ac.uk>
wrote:

> Hello,
>
>
>
> I am conducting an experiment where participants imagine a movement, and I
> am collecting eeg data to analyse the event-related desynchronisation. I
> had a couple of participants’ data that look a bit weird when uploaded on
> EEGLAB. (v. 14.1.1). Data was collected using an ANT eego sport system, and
> it was recorded online with reference to CPz, but was re-referenced offline
> to the average of the two mastoid electrodes. Data was uploaded on EEGLAB
> using the ANT extension (.cnt format).
>
> The data has also been band-pass filtered 2-45 Hz, but the signal looks
> different from the one I collected. I also checked if the original file had
> this same problem (the non-re-referenced one), and yes, it has the same
> problem. I have uploaded the same file (same extension), in brainstorm,
> another Matlab toolbox for EEG analysis, and the signal looks completely
> different.
>
> I also have run the power spectrum analysis on both software, and I looks
> that in EEGLAB, even though I band-pass filter 2-45 Hz, it does not remove
> the 50Hz. On the contrary, in Brainstorm it does remove it.
>
> Do you know what may be the problem here, and why the 50 Hz are not
> removed?
>
>
>
> Kind Regards
>
>
>
> FABIO
>
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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