[Mne_analysis] Covariance and noise density in simulation

[Taylor Williams]

        External Email - Use Caution        

Hello,

I have some questions about how covariance in MNE simulation methods
corresponds to noise density. I'm seeking to construct an ad hoc covariance
matrix that corresponds to a particular noise density at a particular
sampling frequency.

For example, I'd like to simulate evoked data for an MEG array that has 3
fT/sqrt(Hz) white noise density at 600 Hz sampling frequency. Documentation
for create_ad_hoc_cov() states that the default values for magnetometers is
20 fT.

To properly simulate 3 fT/sqrt(Hz) at 600 Hz, should I calculate the total
noise as 3*sqrt(600) = 73.4 fT and scale my cov matrix from 20 fT
accordingly, or do the MNE methods account for system bandwidth in
simulation? Is it common to simulate the full noise bandwidth then apply
filtering to keep the frequency band of interest?

Thanks,
Taylor Williams
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