Is it allowed to apply average reference or other projections after applying Hilbert transform?

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1
  • MNE version: 0.22.0
  • operating system: e.g. macOS 12

Hi,
I used this script on my data:
https://mne.tools/dev/auto_examples/time_frequency/time_frequency_global_field_power.html

After applying hilbert transform:
epochs.apply_hilbert(envelope=True)

I saved the epochs:
epochs.save(‘example-epo.fif’)

When I re-read those epochs I need to specify proj=False to get the same data I saved before:
epochs=mne.read_epochs(‘example-epo.fif’, proj=False)

My question is, is it allowed to apply average reference or other projections after Hilbert transform?

Many thanks,
Ioanna

2

Hi @joanna0811,
If you retain only the envelope of the signal then applying average reference after that is not a good idea. After rereferencing you would get negative values at some channels/timepoints, which does not make sense for envelope (which should contain only non-zero values). I would apply average refere first and only then get the envelope of the signal.

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Thank you very much for taking the time to respond.