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.