Low-frequency oscillation (LFO) is an electronic signal, which is usually below 20 Hz

Hertz

The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

 and creates a rhythmic pulse or sweep. This pulse or sweep is often used to modulate synthesizer

Synthesizer

A synthesizer is an electronic instrument capable of producing sounds by generating electrical signals of different frequencies. These electrical signals are played through a loudspeaker or set of headphones...

s, delay line

Delay line

Delay line may refer to:* Propagation delay, the length of time taken for something to reach its destination* Analog delay line, used to delay a signal...

s and other audio equipment in order to create effects used in the production of electronic music

Electronic music

Electronic music is music that employs electronic musical instruments and electronic music technology in its production. In general a distinction can be made between sound produced using electromechanical means and that produced using electronic technology. Examples of electromechanical sound...

. Audio effects such as vibrato

Vibrato

Vibrato 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 of two factors: the amount of pitch variation and the speed with which the pitch is varied .-Vibrato and...

, tremolo

Tremolo

Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration...

 and phasing

Phaser (effect)

A phaser is an audio signal processing technique used to filter a signal by creating a series of peaks and troughs in the frequency spectrum. The position of the peaks and troughs is typically modulated so that they vary over time, creating a sweeping effect...

 are examples. The abbreviation is also very often used to refer to low-frequency oscillators themselves.

History

Low-frequency oscillation as a concept was first introduced in the modular synth

Modular synthesizer

The modular synthesizer is a type of synthesizer consisting of separate specialized modules connected by wires to create a so-called patch. Every output generates a signal – an electric voltage of variable strength...

s of the 1960s and 70s. Often the LFO effect was accidental; so myriad were the number of 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 instrument

Electronic musical instrument

An electronic musical instrument is a musical instrument that produces its sounds using electronics. Such an instrument sounds by outputting an electrical audio signal that ultimately drives a loudspeaker....

s, such as sampler

Sampler (musical instrument)

A sampler is an electronic musical instrument similar in some respects to a synthesizer but, instead of generating sounds, it uses recordings of sounds that are loaded or recorded into it by the user and then played back by means of a keyboard, sequencer or other triggering device to perform or...

s and software synthesizer

Software synthesizer

A software synthesizer, also known as a softsynth is a computer program or plug-in for digital audio generation. Computer software which can create sounds or music is not new, but advances in processing speed are allowing softsynths to accomplish the same tasks that previously required dedicated...

s, have included LFOs to increase their sound alteration capabilities.

Overview

The primary oscillator

Electronic oscillator

An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. They are widely used in innumerable electronic devices...

 circuits of a synthesizer

Synthesizer

A synthesizer is an electronic instrument capable of producing sounds by generating electrical signals of different frequencies. These electrical signals are played through a loudspeaker or set of headphones...

 are used to create the audio

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

 signals. An LFO is a secondary oscillator that operates at a significantly lower frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 (hence its name), typically below 20hz. This lower frequency or control signal is used to modulate

Modulation

In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...

 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

Sine wave

The sine wave or sinusoid is a mathematical function that describes a smooth repetitive oscillation. It occurs often in pure mathematics, as well as physics, signal processing, electrical engineering and many other fields...

, sawtooth

Sawtooth wave

The sawtooth wave is a kind of non-sinusoidal waveform. It is named a sawtooth based on its resemblance to the teeth on the blade of a saw....

, triangle

Triangle wave

A triangle wave is a non-sinusoidal waveform named for its triangular shape.Like a square wave, the triangle wave contains only odd harmonics...

 or square wave

Square wave

A square wave is a kind of non-sinusoidal waveform, most typically encountered in electronics and signal processing. An ideal square wave alternates regularly and instantaneously between two levels...

. Also like a standard oscillator, LFOs can incorporate any number of waveform types, including user-defined wavetables, rectified wave

Rectifier

A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...

s and random 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

Phase (waves)

Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

, stereo panning, filter

Audio filter

An audio filter is a frequency dependent amplifier circuit, working in the audio frequency range, 0 Hz to beyond 20 kHz. Many types of filters exist for applications including graphic equalizers, synthesizers, sound effects, CD players and virtual reality systems.Being a frequency dependent...

 frequency, or amplification. When routed to control pitch, an LFO creates vibrato

Vibrato

Vibrato 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 of two factors: the amount of pitch variation and the speed with which the pitch is varied .-Vibrato and...

. When an LFO modulates amplitude

Amplitude

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...

 (volume), it creates tremolo

Tremolo

Tremolo, or tremolando, is a musical term that describes various trembling effects, falling roughly into two types. The first is a rapid reiteration...

. On most synthesizers and sound modules, LFOs feature several controllable parameters, which often include a variety of different waveform

Waveform

Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...

s, a rate

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 control, routing options (as described above), a tempo

Tempo

In musical terminology, tempo is the speed or pace of a given piece. Tempo is a crucial element of any musical composition, as it can affect the mood and difficulty of a piece.-Measuring tempo:...

 sync

Synchronization

Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....

 feature, and an option to control how much the LFO will modulate the audio signal.

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

Noise gate

A Noise Gate or gate is an electronic device or software that is used to control the volume of an audio signal. In its most simple form, a noise gate allows a signal to pass through only when it is above a set threshold: the gate is 'open'. If the signal falls below the threshold no signal is...

 envelopes, or controlling the rate of arpeggiation

Arpeggio

An arpeggio is a musical technique where notes in a chord are played or sung in sequence, one after the other, rather than ringing out simultaneously...

.

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

Electronic filter

Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...

'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 would be for various sound effect

Sound effect

For the album by The Jam, see Sound Affects.Sound effects or audio effects are artificially created or enhanced sounds, or sound processes used to emphasize artistic or other content of films, television shows, live performance, animation, video games, music, or other media...

s used in films). Such effects are difficult to describe, and are more understandable when heard. Dubstep

Dubstep

Dubstep is a genre of electronic dance music that originated in south London, England. Its overall sound has been described as "tightly coiled productions with overwhelming bass lines and reverberant drum patterns, clipped samples, and occasional vocals"....

 is a form of electronic music that employs heavy use of LFOs for bass sounds that have a "generic wobble" effect.

Other notes

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