[Mne_analysis] notch filter for removing power chord signal

[Lauri Parkkonen]

Hello,

If I may put my two cents in... Most of the 50/60-Hz interference is 
really the ambient magnetic field. This is the case at least with the 
Elekta Neuromag systems and I believe with most other systems, too. 
Thus, a properly-derived SSP operator should reduce the 50/60-Hz level 
considerably but as such a projection has no notion of time, the same 
spatial filtering is done unnecessarily at all frequencies. If you want 
to keep the spatial patterns as intact as possible, then a notch is a 
better option as Alex pointed out.

Cheers,
Lauri


On 13.09.2012 05:27, sheraz at nmr.mgh.harvard.edu wrote:
> Hi Denis,
>
> As Alex said SSP cant be used to remove line frequency, as its comes from
> electronics.
>
> If you go mne-Matlab way, you can use eegfilt to have notch filter or try
> harmonics filter which works better for line frequency. For reading and
> writing raw fif file look at mne_ex_read_write_raw.m.
>
> sheraz
>
>
>
>> 2012/9/12 Alexandre Gramfort <gramfort at nmr.mgh.harvard.edu>:
>>> hi Denis,
>>>
>>>> I wonder whether there is a MNE-way of removing power-chor artifacts
>>>> from wide-band MEG data (1-200 Hz).
>>> you mean the AC current and the harmonics of 50 or 60Hz?
>> yes.
>>
>>>> As there does not seem to be a notch filter available, empty room SSPs
>>>> might be the way to do it.
>>> yes don't use SSP for this.
>>>
>> ok, thanks though
>>
>>> You need a notch like filter but I am not aware of any with mne or
>>> mne-python.
>>>
>>> Alex
>>>
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