PSD log transformation

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For visualization, when a PSD plot is show, select Display Tab > Measure > Log, this will apply 10*log10(), then the PSD will be in [dB/Hz]

In Brainstorm PSDs are stored in [units2/ Hz] with units being volts [V] (or teslas [T]), to change to decibels [dB/Hz], run:
psd_dB = 10 *log10(psd_V);

The negative values that you're seen have their origin in fact that the PSD in [dB/Hz] is computed on the PSD in [V2/Hz].

To have results in the same units as the shared figure, [10*log10(μV2/Hz)]:

  1. Scale the PSD from [V2/Hz] to [μV2/Hz] by dividing by the squared prefix.
    psd_uV = psd_V / (1e-6)^2;
  2. Then apply 10*log10( )
    10*log10(psd_uV)