# notch filter for removing power chord signal **URL:** \ **Category:** Mailing List Archive (read-only)\ **Tags:** list-archive\ **Created:** [September 12, 2012, 10:07am UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488 "2012-09-12T10:07:36Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [September 12, 2012, 10:07am UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488/1 "2012-09-12T10:07:36Z")
Dear list, I wonder whether there is a MNE-way of removing power-chor artifacts from wide-band MEG data (1-200 Hz). As there does not seem to be a notch filter available, empty room SSPs might be the way to do it. What do you think? Denis ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [September 12, 2012, 3:14pm UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488/2 "2012-09-12T15:14:55Z")
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? > 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. You need a notch like filter but I am not aware of any with mne or mne-python. Alex ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [September 12, 2012, 3:33pm UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488/3 "2012-09-12T15:33:39Z")
2012/9/12 Alexandre Gramfort \: > 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 ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [September 13, 2012, 2:27am UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488/4 "2012-09-13T02:27:42Z")
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 ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [September 13, 2012, 3:29am UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488/5 "2012-09-13T03:29:38Z")
Hi Denis,    The multitaper based rmlinesc() routine in Chronux to remove line noise works well: [http://www.chronux.org/downloads/chronux/chronux/documentation/chronux\_2\_00/spectral\_analysis/continuous/rmlinesc.html](http://www.chronux.org/downloads/chronux/chronux/documentation/chronux_2_00/spectral_analysis/continuous/rmlinesc.html) The following is a reference that describes the technique: [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1300074/](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1300074/) Also, most of the time I don't remove it so when I do time-frequency decompositions I know that I have the scales correctly done when I see the line components at the correct frequency.. Regards, Hari ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [September 13, 2012, 12:38pm UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488/6 "2012-09-13T12:38:31Z")
Dear Sheraz and Hari -- thanks for the good pointers! (I hope you did not receive this already, my mail application was going wild this morning...) 2012/9/13 Hari Bharadwaj \: > Hi Denis, >    The multitaper based rmlinesc() routine in Chronux to remove line noise > works well: > [http://www.chronux.org/downloads/chronux/chronux/documentation/chronux\_2\_00/spectral\_analysis/continuous/rmlinesc.html](http://www.chronux.org/downloads/chronux/chronux/documentation/chronux_2_00/spectral_analysis/continuous/rmlinesc.html) > > The following is a reference that describes the technique: > [Analysis of dynamic brain imaging data. - PMC](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1300074/) > > Also, most of the time I don't remove it so when I do time-frequency > decompositions I know that I have the scales correctly done when I see the > line components at the correct frequency.. Actually very neat. I haven't thought of that.. ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [September 13, 2012, 10:31pm UTC](https://mne.discourse.group/t/notch-filter-for-removing-power-chord-signal/488/7 "2012-09-13T22:31:13Z")
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