Hi there,

I’m relatively new to EEG and signal processing, and am using the Muse for a

school project. To help better my understanding of what the Muse was doing, I

tried to redo the signal processing steps that the Muse performs to report

absolute band powers using data from the research tools exported to CSV format.

Unfortunately, I haven’t been successful in getting the same numbers that the

Muse reports for the FFT. It isn’t important for my project, but I was

wondering if someone might be able to point out where I went wrong.

My understanding is that no FFT is done until the Muse has sent 256 raw EEG data

packets, so I made sure to start recording the data stream in time to pick the

first 256 packets up so that I would know which values were used in the Muse

calculation. I took the first column of the first 256 raw EEG records

(appearing in the data before any FFTs), which I believe correspond to TP9

channel and ran these values through the `rfft`

function provided by the numpy

package for Python.

Since all the inputs are real, it only returns half of the frequency bins since

the others are just reflected about 0 Hz term (as indicated in the docs).

Now, I know that the values reported at /muse/elements/rawfftX are actually based

on the power spectral density. To calculate this, I have done as indicated in

the numpy documentation at http://docs.scipy.org/doc/numpy/reference/routines.fft.html

and transformed the array by computing the square of the magnitude of each

element. Since the inputs were the values from TP9, I would expect this to

produce the first array reported at /muse/elements/rawfft0, but this was not the

case.

I did some digging and saw that Tom mentioned in his first reply here

http://forum.choosemuse.com/forum/technical-support/3406-raw_fft-frequencies-and-themicrovolts-connected-question

that these values are actually the *log* of the PSD, but I don’t know if that is

still the case.

My guess is I did not calculate the PSD correctly, although that seems pretty

straightforward. Would anyone be able to offer another opinion?

Thanks,

Will