extracting high frequency broadband (HFB) envelope

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Hello,

I want to perform event related analysis on some high frequency amplitude of some ECoG signals.

I apply raw.filter() and raw.apply_hilbert(envelope=true) in the frequency band of interest on my initial data.

The resulting HFB envelope contains only positive values, as an amplitude should.

Strangely once I epoch the envelope with mne.epoch() using some equally spaced stimulus releated events, the resulting epochs contain some negative value in their entries. But is does not seems that epoching shift the origin x axis or does it?

I know that I can also extract the envelope directly from epoched data but this a confusing observation and would appreciate some explanation of what could go wrong if anybody has ?

Cheers,

Guillaume Corlouer

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Strangely once I epoch the envelope with mne.epoch() using some equally
spaced stimulus releated events, the resulting epochs contain some negative
value in their entries. But is does not seems that epoching shift the
origin x axis or does it?

Did you set `baseline=None`? The default
<https://mne.tools/dev/generated/mne.Epochs.html#mne.Epochs&gt; is
`baseline=(None, 0.)` which would mean that your data are being baseline
corrected (which you probably don't want).

Eric
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Turns out I didn't set `baseline=None`, indeed I don't want it to be baseline corrected, this solved the problem, thanks a lot !