Voltage-controlled filter

A voltage-controlled filter (VCF) is an electronic filter whose operating characteristics (primarily cutoff frequency) can be set by an input control voltage. Voltage controlled filters are widely used in analogue music synthesizers. A voltage-controlled filter (VCF) is an electronic filter whose operating characteristics (primarily cutoff frequency) can be set by an input control voltage. Voltage controlled filters are widely used in analogue music synthesizers. A music synthesizer VCF allows its cutoff frequency, and sometimes its Q factor (resonance at the cutoff frequency), to be continuously varied. The filter outputs often include a lowpass response, and sometimes highpass, bandpass or notch responses.Some musical VCFs offer a variable slope which determines the rate of attenuation outside the bandpass, often at 6dB/octave, 12dB/octave, 18dB/octave or 24dB/octave (one-, two-, three- and four-pole filters, respectively).In modular analog synthesizers, VCFs receive signal input from signal sources, including oscillators and noise, or the output of other processors. By varying the cutoff frequency, the filter passes or attenuates partials of the input signal. In some popular electronic music styles, 'filter sweeps' have become a common effect. These sweeps are created by varying the cutoff frequency of the VCF (sometimes very slowly). Controlling the cutoff by means of a transient voltage control, such as an envelope generator, especially with relatively fast attack settings, may simulate the attack transients of natural or acoustic instruments.