# No empty room recording

**URL:** <https://mne.discourse.group/t/no-empty-room-recording/1738>\
**Category:** Mailing List Archive (read-only)\
**Tags:** list-archive\
**Created:** [February 12, 2019, 9:25am UTC](https://mne.discourse.group/t/no-empty-room-recording/1738 "2019-02-12T09:25:34Z")\
**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:** [February 12, 2019, 9:25am UTC](https://mne.discourse.group/t/no-empty-room-recording/1738/1 "2019-02-12T09:25:34Z")

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External Email - Use Caution

Hi,  
I'm working with meg data set but I do not have empty room recording.  
How can I compute noise co-variance without empty room recording?  
Can I use identity matrix?

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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:** [February 13, 2019, 5:01pm UTC](https://mne.discourse.group/t/no-empty-room-recording/1738/2 "2019-02-13T17:01:39Z")

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External Email - Use Caution

You can use mne.make\_ad\_hoc\_cov, which creates a diagonal matrix, or use a  
covariance computed from a baseline interval before your events of interest  
(if it's an event-related paradigm).

Eric