# ValueError: SSP projectors in epochs\[1\] must be the same

**URL:** <https://mne.discourse.group/t/valueerror-ssp-projectors-in-epochs-1-must-be-the-same/9273>\
**Category:** Support & Discussions\
**Tags:** meg\
**Created:** [September 2, 2024, 7:36pm UTC](https://mne.discourse.group/t/valueerror-ssp-projectors-in-epochs-1-must-be-the-same/9273 "2024-09-02T19:36:27Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![eort](https://avatars.discourse-cdn.com/v4/letter/e/e56c9b/32.png) [@eort](https://mne.discourse.group/u/eort)\
**Post date:** [September 2, 2024, 7:36pm UTC](https://mne.discourse.group/t/valueerror-ssp-projectors-in-epochs-1-must-be-the-same/9273/1 "2024-09-02T19:36:27Z")

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Hey all,

I have MEG data recorded during different sessions on different days. I have preprocessed the sessions separately, but would like to concatenate epochs from each session into one epochs objects. Unfortunately, it fails because the SSP projectors are different for each session (I used SSPs from empty room recordings instead of the default ones).

I was wondering whether it is legit to ignore this warning and still concatenate the epochs if the projectors are applied before concatenation. Does it matter for further processing if the projectors are different but are already applied?

For reference, I am using mne 1.2.

Thanks,  
Eduard

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**Author:** ![mscheltienne](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/mscheltienne/32/827_2.png) [@mscheltienne](https://mne.discourse.group/u/mscheltienne)\
**Post date:** [September 3, 2024, 7:27am UTC](https://mne.discourse.group/t/valueerror-ssp-projectors-in-epochs-1-must-be-the-same/9273/2 "2024-09-03T07:27:13Z")

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If they are applied, I think you are good to go. I’ll let someone else confirm as well.

Mathieu

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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:** [September 10, 2024, 7:27am UTC](https://mne.discourse.group/t/valueerror-ssp-projectors-in-epochs-1-must-be-the-same/9273/3 "2024-09-10T07:27:59Z")

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Closed on September 10, 2024, 7:27am UTC

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