The Structure of the Electric Guitar
Balancers and notch filters
Balancers adjust sound
Balancers for guitars and bass guitars generally play a role in adjusting the sound that is mixed and output from different types of pickups. In most cases, these are attached to adjust the balance of the front and rear pickups of a bass guitar.
Notch filters prevent feedback
Notch filters are a type of equalizer mainly used to cut certain frequency bands in order to prevent feedback. These are often found in effectors and the like for acoustic guitars.