Science Fair Project Encyclopedia
Low frequency oscillation
Low frequency oscillaton, often abbreviated to LFO, is a term that predominantly refers to an audio technique specifically used in the production of electronic music. In addition to the main oscillator(s) of a synthesizer, which is responsible for the creation of the audio signal itself, an LFO is an additional oscillator that operates at a comparatively lower frequency (hence its name), that modulates the audio signal, thus causing a difference to be heard in the signal without the actual introduction of another sound source. Low Frequency Oscillation as a concept was first introduced in the modular synths of the 1960s and 70s — often its effect was 'accidental'; such were the extensive capabilities of a modular synth operator to patch the instrument to create a vast array of different configurations. They have since appeared in some form on almost every synthesizer, and more recently other electronic instruments such as samplers have included them, to augment their capacity for sound alteration.
The principle behind low frequency oscillation as a means of modulating a signal, as opposed to adding to it, is that its frequency is lower than the audible frequency of the human ear (20Hz–20kHz) i.e., the frequency is low enough so that it isn't heard as a tone.
A low frequency oscillator can be routed to control a variety of different parameters, for example the frequency of the audio oscillator, the phase, panning, filter frequency, or the velocity of the syntheszier's output. On most synthesizers and sound modules, there are several different ways in which the user can alter the effect produced by the LFO. These may include a variety of different waveforms, a rate control, routing options (as described above), a tempo sync feature, and an option to control the amount by which the LFO will modulate the audio signal.
Electronic musicians use LFO for a variety of applications, ranging from adding simple vibrato or tremolo to a melody, to more complex applications such as triggering gate envelopes. Differences between LFO rates also account for a number of commonly heard effects in modern music - for instance, a very low rate can be used to modulate filter 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 effects used in films). However, these effects are difficult to describe, instead they are more understandable simply when heard.
The British electronic music group LFO take their name directly from the concept of low frequency oscillation, its properties doubtlessly influential in their music production.
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