What is LFO?
LFO or Low-frequency oscillation is an electronic frequency which is usually below 20 Hz or at the bottom of the audio range. So, the human ear cannot hear it. It creates a rhythmic pulse or sweep and is often used to modulate synthesizers, delay lines, and other audio equipment to create effects used in the production of electronic music. What’s more, the abbreviation LFO often refers to low-frequency oscillators themselves. Nearly all synthesizers have at least one LFO or a digital equivalent. Moreover, an LFO or a modulation generator does not necessarily deliver a periodic signal but can also be a one-shot type such an envelope generator started by a keypress event.
Modular synths of the 1960s and 70s first introduced low-frequency oscillation as a concept. This effect was often accidental, so there were a lot 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 instruments, such as samplers and software synthesizers, have included LFOs to increase their sound alteration capabilities.
Generating Waveforms and Modulation
LFO is useful for producing a repeating control signal for a wide variety of purposes. It can generate a variety of useful waveforms, including sine, triangle, square, ramp-up, and ramp-down. The most useful ones have an upper-frequency limit above 100 Hz and a lower limit below 1 Hz. It may or may not have voltage control over its frequency or other wave parameters. Therefore, an LFO with voltage control over the frequency is sometimes referred to as a “VCLFO”. Simply stated, LFO is an oscillator producing these waveforms at a very low frequency or pitch. Producers use these slowly vibrating, generally subsonic waves (0 – 20 Hz or so) to modulate or change a parameter in a synth, sampler, or effects processor.
One common application is modulating the pitch of an audio oscillator with an LFO; this results in vibrato. Also, when you add it to the control input of a VCO it produces the effect known as vibrato. If the volume of an audio oscillator is modulated with an LFO, the result is tremolo. Therefore, if you add it to the control signal of a VCA, it produces tremolo. Just about any time you see a “modulation” control on a device, it is controlling an LFO. Therefore, you can use it to change some parameter periodically.
On most synthesizers and sound modules, LFOs feature several controllable parameters. These parameters often include a variety of different waveforms like rate control, routing options, a tempo sync feature, and an option to control how much the LFO will modulate the audio signal. It 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”.
In modern music
Electronic musicians use LFO for a variety of applications. For example, it can add simple vibrato or tremolo to a melody. A more complex application would be triggering gate envelopes or controlling the rate of arpeggiation.
Dubstep and drum and bass are forms of electronic music that employ frequent use of LFOs, often synchronized to the tempo of the track, for bass sounds that have a “wobble” effect. For example, by modulating the cutoff frequency of a low-pass filter to create a distinctive opening-and-closing effect. Due to the popularization of these genres, producers started using this wobble in other forms of electronic dance music such as house music. Producers also commonly use the LFO in future bass music to enhance synthesizers, along with side-chain.
Differences between LFO rates also account for several commonly heard effects in modern music. For example, you can use a very low rate to modulate a filter’s cutoff frequency. It then provides 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. Finally, another important use of LFO is in the movie industry for various sound effects in films.