A voltage-controlled filter (VCF) is an
electronic filter whose operating characteristics (primarily
cutoff frequency
In physics and electrical engineering, a cutoff frequency, corner frequency, or break frequency is a boundary in a system's frequency response at which energy flowing through the system begins to be reduced ( attenuated or reflected) rather tha ...
) can be set by an input
control voltage
CV/gate (an abbreviation of ''control voltage/gate'') is an analog method of controlling synthesizers, drum machines, and similar equipment with external sequencers. The control voltage typically controls pitch and the gate signal controls note ...
. Voltage controlled filters are widely used in
synthesizers.
![Butterworth response](https://upload.wikimedia.org/wikipedia/commons/6/60/Butterworth_response.svg)
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
A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter ...
response, and sometimes
highpass
A high-pass filter (HPF) is an electronic filter that passes signals with a frequency higher than a certain cutoff frequency and attenuates signals with frequencies lower than the cutoff frequency. The amount of attenuation for each frequency d ...
,
bandpass
A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects (attenuates) frequencies outside that range.
Description
In electronics and signal processing, a filter is usually a two-po ...
or
notch responses.
Some musical VCFs offer a variable ''slope'' which determines the rate of attenuation outside the bandpass, often at 6 dB/octave, 12 dB/octave, 18 dB/octave or 24 dB/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
In physics and electrical engineering, a cutoff frequency, corner frequency, or break frequency is a boundary in a system's frequency response at which energy flowing through the system begins to be reduced ( attenuated or reflected) rather tha ...
, 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
In sound and music, an envelope describes how a sound changes over time. It may relate to elements such as amplitude (volume), frequencies (with the use of filters) or pitch. For example, a piano key, when struck and held, creates a near-im ...
, especially with relatively fast attack settings, may simulate the attack transients of natural or acoustic instruments.
Historically, musical VCFs have included variable feedback which creates a response peak (Q) at the cutoff frequency. This peak can be quite prominent, and when the filter's frequency is swept by a control, partials present in the input signal resonate. Some filters are designed to provide enough feedback to go into self-oscillation, and it can serve as a sine-wave source.
ARP Instruments
ARP Instruments, Inc. was a Lexington, Massachusetts manufacturer of electronic musical instruments, founded by Alan Robert Pearlman
in 1969. It created a popular and commercially successful range of synthesizers throughout the 1970s before de ...
made a multifunction voltage-controlled filter module capable of stable operation at a Q over 100;
it could be shock-excited to ring like a vibraphone bar. Q was voltage-controllable, in part by a panel-mounted control. Its internal circuit was a classic analog computer state variable "loop", which provided outputs in quadrature.
A VCF is an example of an
active
Active may refer to:
Music
* ''Active'' (album), a 1992 album by Casiopea
* Active Records, a record label
Ships
* ''Active'' (ship), several commercial ships by that name
* HMS ''Active'', the name of various ships of the British Royal ...
non-linear filter
In signal processing, a nonlinear (or non-linear) filter is a filter whose output is not a linear function of its input. That is, if the filter outputs signals ''R'' and ''S'' for two input signals ''r'' and ''s'' separately, but does not always o ...
. The characteristic musical sound of a particular VCF depends on both its linear (small-signal) frequency response and its non-linear response to larger amplitude inputs.
Synthesizer filter types
*
Transistor ladder filter
*
Diode ladder filter
*
Sallen-Key filter
*
OTA filter OTA or ota may stand for:
Art, entertainment, and media
* '' Off the Air'', an Adult Swim television series
* Otakon, an annual anime convention in Baltimore, Maryland
Electronics, science, and technology
* Ochratoxin A (also termed OTA), a myco ...
See also
*
Audio filter
An audio filter is a frequency dependent circuit, working in the audio frequency range, 0 Hz to 20 kHz. Audio filters can amplify (boost), pass or attenuate (cut) some frequency ranges. Many types of filters exist for different audio a ...
*
Electronic filter
*
Electronic filter topology
Electronic filter topology defines electronic filter circuits without taking note of the values of the components used but only the manner in which those components are connected.
Filter design characterises filter circuits primarily by their ...
*
Non-linear filter
In signal processing, a nonlinear (or non-linear) filter is a filter whose output is not a linear function of its input. That is, if the filter outputs signals ''R'' and ''S'' for two input signals ''r'' and ''s'' separately, but does not always o ...
*
Self oscillation
Self-oscillation is the generation and maintenance of a periodic motion by a source of power that lacks any corresponding periodicity. The oscillator itself controls the phase with which the external power acts on it. Self-oscillators are therefor ...
*
Subtractive synthesis
Subtractive synthesis is a method of sound synthesis in which partials of an audio signal (often one rich in harmonics) are attenuated by a filter to alter the timbre of the sound. While subtractive synthesis can be applied to any source audio ...
*
Voltage-controlled amplifier
A variable-gain (VGA) or voltage-controlled amplifier (VCA) is an electronic amplifier that varies its gain depending on a control voltage (often abbreviated CV).
VCAs have many applications, including audio level compression, synthesizers and ...
*
Voltage-controlled oscillator
A microwave (12–18GHz) voltage-controlled oscillator
A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscilla ...
References
{{reflist
External links
Schematics and PCBs for building your own VCF
Nonlinear filters
Synthesiser modules