Low-frequency oscillation (LFO) is a term used in the field of audio signal processing to refer to periodic, cyclic variations in a signal with a frequency below 20 Hz. This type of oscillation is often used to modulate synthesizers, effects units and other audio equipment in order to create a wide variety of sounds and effects. LFOs can also be used to modulate the frequency of an oscillator, allowing for the creation of vibrato, tremolo and other modulation effects.