Unit of Measurement for EEG data after FFT

[Misino Augusto]

When using EmotivPRO Analyzer, and applying FFT (Fast Fourier Transform), it returns the average power of each frequency band.

BUT…

What is the unit of measurement for that Average Power?
Is it measured in µV or µV^2/Hz, or in dB ?

And, the values… What range shold have? Positive and Negative numbers, or only Positive?

Should one apply a method of normalization after applying FFT ??

 

[Misino Augusto]

So… inspecting the page Band Power calculation | EmotivPRO Analyzer

found a part of code:

band = list(range(16, 25))
band_power = np.sum(eeg_fft_square_3d[band, :, :], axis=0) / len(band)
//Finally EmotivPRO Analyzer will output band power in decibels (dB):
band_power_db = 10*np.log10(band_power))

—————-

They are using a variation of the Logarithmic transformation:
P_dB = 10 * log_⁡10 ⁣( P / P_ref)

Emotiv replaces the ” /P_ref ” with “/ len(band)”.

On the paper Time-frequency analysis methods and their application in developmental EEG data;  it explains that “researchers generally use the decibel conversion … to baseline normalize raw total power values”.
Meaning that “P_ref” is equal to a Baseline Activity.

But Emotiv is using “len(band)”, where: band = list(range(16, 25)).

In Python, len(list(range(16, 25))) returns 9…

Maybe the code in the gitbook manual is just an example, but nevertheless I’m confused about this change (using the lenght of a list intead of a eeg reference).

If someone from Emotiv or someone from the community with more experience can help me understand this, I will be very grateful.

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