Problem regarding the EEG signals captured
hansamali_paul
Sril Lnkan
in Headware
recently, I brought an OpenBCI headband kit with 8 electrodes. when I record the EEG signals and plot it it with mne the signal showed an uptrend as in the image EEG_raw_signal. the signal was saved in the format of .bdf. same problem goes when I save the file with OpenBCI txt form.
I tried to plot the Power Spectral density plot too and in the plot it shows that the power is gone below 0 as shown in the image EEG_raw PSD.
This is the hardware set up of the device (hardware setup).
please give me a solution to this problem.
Comments
Paul, hi.
The recording / raw data files from the GUI, are RAW. NO filters have been applied. You need to use a DSP library (digital signal processing) that has filters to apply, at the minimum: say a bandpass from .5 Hz to 40 Hz. And a notch filter at your mains frequency, 50 Hz. The first image shows both tremendous mains noise, and the DC offset potential slowly increasing. The offset represents frequencies below .5 Hz.
William
https://openbci.com/forum/index.php?p=/discussion/201/large-millivolt-data-values-fbeeg-full-band-eeg
I used the filters as you asked to my raw EEG signal and below is the plot I got (filtered signal). when I plot the power spectrum still the power goes below 0 (psd filtered signal).
I used the filters as you asked to my raw EEG signal and below is the plot I got (filtered signal). when I plot the power spectrum still the power goes below 0 (psd filtered signal).
Read the link I posted. Cannot see your FFT / PSD graph. If you apply the filters correctly everything should look identical to what you saw on the GUI with your filter settings there.
Suggest trying a different FFT graphing routine.