- Bandpass Filter
Bandpass filters only allow frequencies that fall within a certain range to pass through, frequencies outside this range are attenuated or completely silenced. The range of frequencies that pass through is called the filters bandwidth.
- Notch Filter
Notch filters (also known as Band-stop or Band-reject filters) are the inverses of bandpasses, in that all frequencies pass through except those that fall within a certain range.
- Allpass Filter
Allpass filters allow all frequencies to pass through without affecting their amplitude, but their phase (for simplicity you can think timing information) is changed. Whilst not common by themselves, Allpass filters are used as the basis of Phasers and some more specialised filtering processes.