Filtering modifies the frequency spectrum of a signal.
Filters reduce or boost the volume of a signal at a particular
frequency or band of frequencies. The various functional types of filter are named
according to their effect :
Low Pass : cuts frequencies above a certain frequency
High Pass : cuts frequencies below a certain frequency
Band Pass : cuts frequencies outside a certain band
Peaking : boosts frequencies within a certain range.
Notch : cuts completely frequencies a certain value.
Shelving : cuts or boosts below or above a certain value.