LFO (Low-Frequency Oscillator)

An LFO, or low-frequency oscillator, is usually a control signal rather than a tone you listen to directly. It repeatedly raises and lowers a chosen parameter, adding motion to a synthesizer or effect.

Destination, rate and depth

The destination is what moves. Modulating pitch can create vibrato; modulating loudness can create amplitude tremolo; modulating a filter's cutoff changes brightness. A pan destination moves the sound through the stereo field.

The rate says how quickly the cycle repeats, in hertz or in note values synchronized to a tempo. The depth says how far the parameter moves. A small depth may add subtle life, while a large one creates an obvious effect.

Shape and timing

A smooth sine or triangle shape gives a back-and-forth movement. A square shape jumps between values. Some instruments also offer random modulation. An LFO may run freely or restart when a note begins, which changes how repeated notes behave.

Unlike a typical ADSR envelope, which follows a note's onset and release, an LFO normally cycles. The distinction is about use, not a rigid speed limit: some LFOs can run fast enough to enter the audible range and create more complex modulation effects.