[Mne_analysis] The default SSP operator?

[Tsung-Ren Huang]

Hi MNE experts,

We're currently analyzing ongoing spontaneous MEG data.
According to the MNE manual, the recommended SSP operator
is constructed from the empty room measure.

However, before we load in that empty-room SSP onto the task data,
mne_browse_raw seems to apply a default SSP already becuase the raw
data appear very different when we switch off the (default) SSP.

It's not clear to us how this default SSP is computed
and if this default SSP should also be turned off before the
judge of bad channels for the task raw data.

Any hints or information on this will be highly appreciated!

Many thanks,
Tren