High low-frequency energy in EEG signal
I am trying to use cyton to measure EEG signals. What puzzles me is that the signal quality looks good, but the frequency spectrum of the signal looks strange. Below is the spectrum distribution I got by python. You can see that the alpha brain waves are around 10 Hz. However, there is high energy in the low frequency region, which is very unreasonable in my opinion. I have performed 1Hz-40Hz band-pass filter on the data before drawing.
Please tell me if this is normal. If not please tell me how to fix it.