Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A voltage-controlled filter (VCF) is a filter whose operating characteristics can be controlled by means of a control voltage applied to one or more inputs.A VCF allows its cutoff frequency and Q factor to be continuously varied; it usually gives a lowpass response, but may also be switchable to allow highpass, bandpass or even notch responses. The filter may offer a switchable slope which determines how intensely signals outside the pass band become attenuated, usually 12dB/octave (a ''2 pole'' filter) or 24dB/octave (a ''4 pole'' filter).