Is it normal that EEG values get extremely small after filtering and ICA?

Hello everyone,

I am doing basic preprocessing on my EEG data (just filtering & ICA), and I noticed that the values get really small. Is that normal?

raw data:

after filtering:

after ICA:

Am I doing something wrong? My whole code can be found here: Calculate spectral density


Hi @lrajos,
I think this is ok - by filtering you remove a lot of the slow fluctuations in the signal, so you reduce the variance. When cleaning data with ICA you most frequently also remove low-frequency artifacts like eye movements, blinks. However to see if the signal is ok after these steps I would advice to look at the signal, but not the raw values, but line plots like raw.plot(). It is really hard to say if the data looks ok only by looking at dataframes/excel tables without any visualization.