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Hi Natalie,
In most systems, data acquisition (DACQ) sets automatically the linefreq tag.
Command ‘/neuro/bin/util/show_fiff –vt235 filename.fif’ returns the line frequency, or nothing if it was not set.
MaxFilter option –linefreq is effective only with jobs –headpos or –movecomp, and it does not set anything in the FIFF file.
If it was not set in DACQ, strong line frequency artifacts may distort the cHPI signal estimation. Therefore, you can add –linefreq 50 (or 60) to improve the
HPI coil signal model: Continuous HPI signal extraction becomes more accurate when both coil frequencies and line frequency harmonics are incorporated in the sin/cos-wave model.
Thus, option –linefreq does not cause any filtering; instead, you can use option –‘hpisubt amp/line/off’ (together with –headpos or –movecomp) to define if the
line frequency harmonics are subtracted or not.
Best regards, Jukka
From: Announcement for the Neuro MEG list [mailto:[log in to unmask]]
On Behalf Of Natalie Klein
Sent: 28. kesäkuuta 2015 23:58
To: [log in to unmask]
Subject: Maxfilter linefreq option
Hi all,
I am looking for clarification on what the Maxfilter -linefreq option does.
The Maxfilter 2.2 manual is unclear to me. The only mentions of the option are:
"The line frequency and its harmonics are included with the option -linefreq lf." and "Sets the basic line interference frequency (50 or 60 Hz)."
The mne-python documentation (in the preprocessing/maxfilter.py file on the github), says:
"linefreq : int (50, 60) (or None), Sets the basic line interference frequency (50 or 60 Hz) (None: do not use line filter)"
This suggests that the linefreq option actually implements some kind of filtering.
So does using the linefreq option in Maxfilter actually filter out line noise, or does it simply set the value of linefreq into the FIF object? I'm trying to determine if I still need to filter out line noise after using Maxfilter.
Thank you,
Natalie Klein
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Jukka Nenonen |
Method Development Manager |
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