Voltage-controlled filter

A voltage- controlled filter ( engl. voltage -controlled filter, short VCF ) is an electronic filter with which the corner frequency can be varied by means of a control voltage ( engl. cut off).

The transition frequency, or the cut-off frequency is the frequency at which the input signal by an amount of 3 dB in the level is lowered.


VCFs are elementary circuit components of synthesizers and effects devices in the electronic music. In modular synthesizers they correspond to separate modules, which can be switched between Voltage Controlled Oscillator and Voltage Controlled Amplifier (VCA ). As a type of filter used in synthesizers usually low-pass filter, rare high-pass, band-pass or all-pass filters are used. The filters are usually summarized in time-controlled via envelopes and can of course be of any other control voltage as influence by Low Frequency Oscillator (LFO ). In the digital age VCFs and LFOs are usually modeled digitally, a data stream is then instead of the control voltage loss.

Typical VCF in addition to the change of tone color by the filter cutoff frequency, the adjustable filter response, that corresponds technically a feedback in the area of the cutoff frequency of the output signal ( depending on the phase shift of the signal through the filter depending on the frequency, the result is reinforcement or attenuation of the signal ).

Among the most famous VCFs probably one of the cascade filter by Robert Moog. It is constructed as a cascade transistor functioning as 24 dB low-pass filter and generates an unmatched tone. Another famous example is the filter of the Roland TB -303, an analog bass synthesizer made ​​famous by the techno music with bass lines that, depending on the setting of filter cutoff and resonance, rather " bubble " or rather " screech ".

  • Filter ( Electrical Engineering)
  • Sound synthesis