[MNE analysis] psd_welch

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Dear MNE team,

I have some doubts about the units psd_welch returns for the PSD as my
output values have a magnitude of 10**-11/-12 and I'd like to get the same
values in dB that are displayed in the plot when using:

rawB0939_copy.plot_psd(fmin=0.5,fmax=30)

Maximum values I get in the plot in the range of 0-4 Hz are around 15 to
25 dB, using the different dB (True/False) and estimation
(auto,power,amplitude) options.

I use this line of code to compute psd values:
psd_delta,freqs_delta=time_frequency.psd_welch(rawB0939_copy,fmin=0.5,fmax=4)

Thank you for your help,

Lidia

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Is it perhaps just a problem of units? The plotters typically scale things
to show data in uV or fT, whereas data on disk (and thus returned by
`psd_welch` et al.) are stored in the objects in SI units (V, T).

Eric