What is a voltage-controlled filter (VCF)?
1 Answer
A voltage-controlled filter (VCF) is an electronic circuit used in audio signal processing and synthesis to control the frequency content of a signal. It is a type of filter whose cutoff frequency can be controlled by a voltage input. VCFs are commonly found in analog synthesizers and modular synthesizer systems, though they can also be implemented in digital form.
The primary function of a VCF is to attenuate or pass certain frequency components of an input audio signal while attenuating others. The cutoff frequency determines the point at which the filter begins to attenuate frequencies. When the cutoff frequency is low, the filter lets through the lower frequencies and attenuates the higher ones. Conversely, when the cutoff frequency is high, the filter allows higher frequencies to pass while attenuating the lower ones.
The most common types of voltage-controlled filters are:
Low-pass filter (LPF): Allows frequencies below the cutoff to pass through while attenuating higher frequencies.
High-pass filter (HPF): Allows frequencies above the cutoff to pass through while attenuating lower frequencies.
Band-pass filter (BPF): Allows frequencies within a certain range centered around the cutoff to pass through while attenuating frequencies outside that range.
Notch filter (or band-reject filter): Attenuates frequencies within a certain range centered around the cutoff while allowing frequencies outside that range to pass through.
All-pass filter: Allows all frequencies to pass through but alters the phase relationship between the input and output signals.
The cutoff frequency of the VCF can be controlled by applying a control voltage to the filter's designated input. This voltage can be generated by various sources, such as envelope generators, low-frequency oscillators (LFOs), sequencers, or other control modules in a modular synthesizer system. By modulating the cutoff frequency over time with changing control voltages, the VCF can produce dynamic and expressive timbral changes to the audio signal, making it a powerful tool for sound shaping and synthesis.
The primary function of a VCF is to attenuate or pass certain frequency components of an input audio signal while attenuating others. The cutoff frequency determines the point at which the filter begins to attenuate frequencies. When the cutoff frequency is low, the filter lets through the lower frequencies and attenuates the higher ones. Conversely, when the cutoff frequency is high, the filter allows higher frequencies to pass while attenuating the lower ones.
The most common types of voltage-controlled filters are:
Low-pass filter (LPF): Allows frequencies below the cutoff to pass through while attenuating higher frequencies.
High-pass filter (HPF): Allows frequencies above the cutoff to pass through while attenuating lower frequencies.
Band-pass filter (BPF): Allows frequencies within a certain range centered around the cutoff to pass through while attenuating frequencies outside that range.
Notch filter (or band-reject filter): Attenuates frequencies within a certain range centered around the cutoff while allowing frequencies outside that range to pass through.
All-pass filter: Allows all frequencies to pass through but alters the phase relationship between the input and output signals.
The cutoff frequency of the VCF can be controlled by applying a control voltage to the filter's designated input. This voltage can be generated by various sources, such as envelope generators, low-frequency oscillators (LFOs), sequencers, or other control modules in a modular synthesizer system. By modulating the cutoff frequency over time with changing control voltages, the VCF can produce dynamic and expressive timbral changes to the audio signal, making it a powerful tool for sound shaping and synthesis.