FFT frequency bins

1

Hello,

I see there are default values for the FFT frequency bins. What is the logic for these defaults (copied below)? For example, why is there no 4-5 or 29-30 overlap, and no 13-14 frequency?

delta / 2, 4 / mean
theta / 5, 7 / mean
alpha / 8, 12 / mean
beta / 15, 29 / mean
gamma1 / 30, 59 / mean
gamma2 / 60, 90 / mean

Thanks!
Dustine

2

This definition of frequency bands is a convention, and it excludes some frequency bins between bands, yes. Feel free to redefine these bands according to your needs and/or your reference literature.

You can reduce the gap between bands, but I don't recommend using any explicit overlap.
If you define frequency bands with an overlap, some bins might be considered in 2 different frequency bands. If you use delta=2-5 and theta=5-2, then if you have a bin at exactly 5Hz, it would be considered twice.

Then, when using the Morlet wavelet for time-frequency decomposition by frequency bands, having bounds that are too close is a problem with the method we are using. We compute the wavelet transformation at 4 frequencies equally spaced in the band (including the bounds) and average the result. If the last frequency of your delta band is the same as the first as the first frequency of your theta band, then it's going to cause some unwanted leakage between your bands.