Low-frequency Oscillation
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Low-frequency oscillation (LFO) is an electronic
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is ...
that is usually below 20  Hz and creates a rhythmic pulse or sweep. This is used to modulate musical equipment such as
synthesizer A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis ...
s to create audio effects such as
vibrato Vibrato (Italian, from past participle of " vibrare", to vibrate) is a musical effect consisting of a regular, pulsating change of pitch. It is used to add expression to vocal and instrumental music. Vibrato is typically characterised in terms o ...
, tremolo and phasing.


History

Low-frequency oscillation was introduced with modular synthesizers of the 1960s, such as the Moog synthesizer. Often the LFO effect was accidental, as there were myriad configurations that could be "patched" by the synth operator. LFOs have since appeared in some form on almost every synthesizer. More recently other electronic musical instruments, such as
sampler Sampler may refer to: * Sampler (signal), a digital signal processing device that converts a continuous signal to a discrete signal * Sampler (needlework), a handstitched piece of embroidery used to demonstrate skill in needlework * Sampler (surna ...
s and software synthesizers, have included LFOs to increase their sound alteration capabilities.


Overview

The primary oscillator circuits of a
synthesizer A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis ...
are used to create the audio signals. An LFO is a secondary oscillator that operates at a significantly lower
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is ...
(hence its name), typically below 20 Hz - that is, below the range of human hearing. This lower frequency or control signal is used to modulate another component's value, changing the sound without introducing another source. Like a standard oscillator, this usually takes the form of a periodic waveform, such as a sine, sawtooth,
triangle A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC. In Euclidean geometry, any three points, when non- colli ...
or
square wave A square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same duration at minimum and maximum. In an ideal square wave, the transitions b ...
. Also like a standard oscillator, LFOs can incorporate any number of waveform types, including user-defined wavetables, rectified waves and
random In common usage, randomness is the apparent or actual lack of pattern or predictability in events. A random sequence of events, symbols or steps often has no order and does not follow an intelligible pattern or combination. Individual rando ...
signals. Using a low-frequency oscillation signal as a means of modulating another signal introduces complexities into the resulting sound, such that a variety of effects can be achieved. The specifics vary greatly depending on the type of modulation, the relative frequencies of the LFO signal and the signal being modulated, et cetera.


Uses

An LFO can be routed to control, for example, the frequency of the audio oscillator, its phase, stereo panning, filter frequency, or amplification. When routed to control pitch, an LFO creates
vibrato Vibrato (Italian, from past participle of " vibrare", to vibrate) is a musical effect consisting of a regular, pulsating change of pitch. It is used to add expression to vocal and instrumental music. Vibrato is typically characterised in terms o ...
. When an LFO modulates
amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of a ...
(volume), it creates tremolo. On most synthesizers and sound modules, LFOs feature several controllable parameters, which often include a variety of different
waveform In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electron ...
s, a
rate Rate or rates may refer to: Finance * Rates (tax), a type of taxation system in the United Kingdom used to fund local government * Exchange rate, rate at which one currency will be exchanged for another Mathematics and science * Rate (mathema ...
control, routing options (as described above), a
tempo In musical terminology, tempo ( Italian, 'time'; plural ''tempos'', or ''tempi'' from the Italian plural) is the speed or pace of a given piece. In classical music, tempo is typically indicated with an instruction at the start of a piece (ofte ...
sync feature, and an option to control how much the LFO will modulate the audio signal. LFOs can also be summed and set to different frequencies to create continuously changing slow moving waveforms, and when linked to multiple parameters of a sound, can give the impression that the sound is "alive". Electronic musicians use LFO for a variety of applications. They may be used to add simple vibrato or tremolo to a melody, or for more complex applications such as triggering
gate A gate or gateway is a point of entry to or from a space enclosed by walls. The word derived from old Norse "gat" meaning road or path; But other terms include '' yett and port''. The concept originally referred to the gap or hole in the wal ...
envelopes, or controlling the rate of arpeggiation. Differences between LFO rates also account for a number of commonly heard effects in modern music. A very low rate can be used to modulate a filter's cutoff frequency, thereby providing the characteristic gradual sensation of the sound becoming clearer or closer to the listener. Alternatively, a high rate can be used for bizarre 'rippling' sound effects (indeed, another important use of LFO is for various sound effects used in films). Dubstep and drum and bass are forms of electronic music that employ frequent use of LFOs, often synchronized to the
tempo In musical terminology, tempo ( Italian, 'time'; plural ''tempos'', or ''tempi'' from the Italian plural) is the speed or pace of a given piece. In classical music, tempo is typically indicated with an instruction at the start of a piece (ofte ...
of the track, for bass sounds that have a "wobble" effect. For example, by modulating the cutoff frequency of a
low-pass filter 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 filt ...
to create a distinctive opening-and-closing effect. Due to the popularization of these genres, the LFO wobble is now being found in other forms of electronic dance music such as
house music House is a music genre characterized by a repetitive four-on-the-floor beat and a typical tempo of 120 beats per minute. It was created by DJs and music producers from Chicago's underground club culture in the late 1970s, as DJs began altering ...
. LFO is commonly used in future bass music to enhance synthesisers, along with side-chain.


In popular culture

The British electronic music group LFO take their name directly from the low-frequency oscillator.


See also

* Audio filter * Modular synthesizer *
Oscillation Oscillation is the repetitive or Periodic function, periodic variation, typically in time, of some measure about a central value (often a point of Mechanical equilibrium, equilibrium) or between two or more different states. Familiar examples o ...
*
Synthesizer A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis ...


References

{{DEFAULTSORT:Low-Frequency Oscillation Electronic music Synthesiser modules