I’m puzzled by the fact that the OpenBCI Processing app has both a 1–50Hz bandpass and a 60Hz bandstop filter applied by default.
I know that the 1–50Hz is to remove the DC offset, and the 60Hz (or optional 50Hz) notch is to remove interference from mains power. But 60Hz is already cut off by the bandpass, so it shouldn’t make any difference. And if they have the 60Hz notch, why not open up the bandpass to, say, 1–100Hz, and let Gamma activity get through? And if it’s already bandpassed, why the “max frequency” button. What’s that about?
I thought it was just a design redundancy, but when I run data into BrainBay, I found that if I just had the bandpass there was wild interference, which was removed by a 59–60Hz notch following it!
Can anyone explain what I’ve overlooked here?