LFO
A low frequency oscillator used to cyclically modulate sound parameters such as pitch or volume.
What it means
LFO stands for low frequency oscillator. It is a signal generator whose frequency usually lies below the audible range, often between 0.1 and 20 hertz. Unlike an audio oscillator, an LFO does not produce an audible tone of its own but a periodic control signal.
This control signal is routed to a sound parameter on a synthesizer or effects unit and modulates it cyclically, typically as a sine, triangle or square wave.
Musical use
When an LFO is routed to pitch, it produces vibrato; when it modulates volume, it produces tremolo; when it controls a filter's cutoff frequency, it produces a rhythmic movement of timbre often heard in electronic dance music. LFOs have been a basic building block of sound synthesis since the analogue synthesizers of the 1960s and 1970s and are found today in virtually every software and hardware instrument.
An LFO should be distinguished from an envelope generator, which also shapes a parameter over time but follows a one-off contour rather than repeating periodically.
Performance practice
On a synthesizer, try routing the same LFO to pitch, volume and filter in turn to compare the different sonic effects directly. Also vary the LFO speed to hear the transition from a slow wobble to a fast, rhythmic flutter.