# noise covariance matrix

**URL:** <https://mne.discourse.group/t/noise-covariance-matrix/17>\
**Category:** Mailing List Archive (read-only)\
**Tags:** list-archive\
**Created:** [October 30, 2007, 7:52pm UTC](https://mne.discourse.group/t/noise-covariance-matrix/17 "2007-10-30T19:52:44Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\
**Post date:** [October 30, 2007, 7:52pm UTC](https://mne.discourse.group/t/noise-covariance-matrix/17/1 "2007-10-30T19:52:44Z")

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Dear MNE specialists,

I am new to MNE and MEG and I am going to analyze coherence on the MEG  
data that were originally supposed to be analyzed as averaged ERPs. For  
this purpose I need to analyze non-averaged (ongoing, spontaneous ) MEG.  
Page 34 of the MNE manual says that in the case of ongoing MEG the noise  
covariance matrix should be calculated based on the empty room  
measurements. Unfortunately, when the data were collected they were not  
supposed to be analyzed as ongoing activity and the empty room  
measurements were not done.  
Can I still analyze coherence on this data? What kind of noise weighting  
can be used in this case?

Elena

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<div class="post-metadata">

**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\
**Post date:** [October 30, 2007, 8:10pm UTC](https://mne.discourse.group/t/noise-covariance-matrix/17/2 "2007-10-30T20:10:20Z")

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Hi Elena

there is an empty room measurement made everyday by the MEG tech, Monday thru Friday, so if you have the dates your subjects were run then we can look up the empty room measurements for that day, I think you can use that file for your the noise covariance matrix.

Deirdre

> > > \<elena at nmr.mgh.harvard.edu\> 10/30/2007 3:52 PM \>\>\>

Dear MNE specialists,

I am new to MNE and MEG and I am going to analyze coherence on the MEG  
data that were originally supposed to be analyzed as averaged ERPs. For  
this purpose I need to analyze non-averaged (ongoing, spontaneous ) MEG.  
Page 34 of the MNE manual says that in the case of ongoing MEG the noise  
covariance matrix should be calculated based on the empty room  
measurements. Unfortunately, when the data were collected they were not  
supposed to be analyzed as ongoing activity and the empty room  
measurements were not done.  
Can I still analyze coherence on this data? What kind of noise weighting  
can be used in this case?

Elena