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

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

, 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 ...

References

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External links

Schematics and PCBs for building your own VCF
Nonlinear filters Synthesiser modules

Synthesizer filter types

See also

References

External links