Shifted alpha peak at 13.5Hz

edited May 9 in Ganglion

I purchased my Ganglion in spring 2023. Recently, I noticed that something seems off about its EEG. Upon further experimentation, using completely new gold plated cups, I noticed that my "alpha" peak at O1 (left earlobe reference, right earlobe ground) seems to be at 13.5Hz (band ~12-15Hz). I.e. that is the frequency that lifts the most when I close my eyes. It's alpha in the sense that it behaves like alpha, it responds to my eyes closing, which other frequencies don't. This is in Brainbay.

I have done a qEEG earlier and I am confused because the results aren't consistent with what I am getting using my Ganglion. The qEEG shows a peak around 10Hz (as would be expected). Brainbay gives me 13.5Hz (the design is just a 2-40Hz bessel bandpass filter [order 8] -> FFT). In OpenBCI GUI I get an FFT plot that seems to make sense, but it's just a snapshot so it could potentially not be representative.

Any guidance on what could be going wrong is appreciated.

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Hi Blue,

    I would suspect your BrainBay design, might be impacted by possible noise issues. For example mains noise may contaminating your output graphs. Are you applying in addition to the bandpass, a notch filter at your mains frequency?

    William

  • edited May 10

    Hi! Thanks for taking an interest.

    I added a 45-55Hz (butterworth) bandstop without much success (consistent with the mains frequency in my country). I am also sitting a bit about a meter away from my laptop and monitor. The image shows the important part of the design (bandstop -> bandpass -> fft) and how the FFT plot changes after I've closed my eyes.

  • wjcroftwjcroft Mount Shasta, CA

    It is sometimes difficult to check the eyes-closed alpha generation on YOURSELF. It other words, best alpha generation depends on your quieting your mind, not merely closing eyes. If you are busy wondering if 'it will work', if your equipment setup is right, etc. All of that pulls the EEG up into beta 15 Hz and higher.

    So you might try a test with a friend who can relax while being measured.

    Is your Brainbay using the Brainflow drivers? There might be more than one device choice in their menus.

    I also assume Brainbay is compatible with your Ganglion firmware. There was a firmware upgrade made available around August / September 2023. But since Brainbay is not often updated, best to stick with your original spring 2023 firmware.

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