Problems with FFT processing of EEG signals.

[Insightque]

I tried to output alpha, beta, gamma, theta values ​​from Muse2 EEG using neurofeedback.py in the example folder.
However, all signals showed similar output as shown in the graph below.

The absolute magnitude of each signal value in the resulting graph varies with frequency.
But I wonder if there is a problem with signal processing if the shape is similar for all frequencies.
The paid app, muse monitor, draws graphs differently depending on the frequency.

I wonder if it's a problem with the settings for FFT calculation, or something else.
I used the master branch without any other configuration parameter changes.

We look forward to advice from experienced people.
Thank you.