# Band Power calculation

The EmotivPRO Analyzer allows the following operations that involve the pre-processing and bandpower extraction.

Basic EEG processing

Basic EEG processing and Transformation

Individual Band-Power Reports

Band Power Report

**Limit slew rate :**

This limits the step change between 2 samples. Analyzer applies a slew rate limitation at 30 µV.

**High-pass filter : **

The data is high-pass filtered before performing the fourier transform. We use the following coefficients ( 3dB at 0.5Hz filter):

**Re-referencing:
**Analyzer supports three ways of re-referencing the EEG data. Interquartile mean (IQM), Median, and Mean.

**Hanning Window :
**Users can choose a window size of N (e.g. 256) samples and this window by M (e.g. 16) samples to create the new window.

The exact implementation of the Hanning window we use:

**Band Powers and Normalization :**

Our normalization uses python and numpy.

Multiplying the Hanning window by 2 (as the window reduces the amplitude of the Fourier transform by a factor of 2 and divide the output of the fft by the window length)

We also subtract the mean of the data for each epoch/window as the DC value is not usable and only distorts the Fourier transform of the lower frequencies.

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