Should we use 60 Hz notch-filter if I just use the frequency lower than 60 Hz?

I am confusing about a 60 Hz notch-filter.

When we use EEG signals, all waves (Delta, theta, alpha, beta, gamma) are located lower than 60 Hz. For example, alpha wave ranges from 8 to 12.99 Hz and beta wave ranges from 13 to 29.99 Hz. Thus, when we extract the frequency for analysis, the frequency does not include 60 Hz frequency. (If alpha wave, it’s 8 to 12.99 Hz - so it does not include a power line noise)

So I think that applying a 60 Hz notch-filter has no effect to the analysis result, but most papers use a notch-filter to remove a power line noise. In the situation above, what is the role of a notch filter?

Taejin, hi.

Your notch filter should be at your local power line mains frequency. So in the US that is 60 Hz, but in many other areas is 50 Hz.

Notch filter is generally recommended, because without it, the mains noise can actually cause “subharmonics” that pollute the signal even below the mains frequency. This is because the mains noise is of such high amplitude, that it forms cross modulation products with other circuit elements.

http://www.erlphase.com/downloads/application_notes/Understanding_Sub_Harmonics.pdf

Regards, William

This is also considered a “nonlinear oscillation”, see,

https://www.google.com/search?q=Nonlinear+Oscillations+subharmonic