Synthesis · glossary
LFO
Also called low frequency oscillator, modulation, wobble
An LFO (low-frequency oscillator) is a slow repeating wave, usually under 20 Hz, that a synth uses to move one of its own settings up and down on a loop: pitch for vibrato, volume for tremolo, or filter cutoff for a wah or wobble.
An LFO makes much the same wave shapes as a synth’s main oscillator, only too slowly to hear as a pitch, usually somewhere between one cycle every ten seconds (0.1 Hz) and about 20 cycles a second. You never hear the LFO itself. You hear what it does to the setting it is connected to.
The target decides the effect:
| Target | What you hear |
|---|---|
| Pitch | Vibrato: the note wavers |
| Volume | Tremolo: the note pulses |
| Filter cutoff | A wah, a slow sweep or a wobble bass |
| Pulse width | A shimmering, chorus-like tone |
| Pan | The sound moves side to side |
Two controls set the movement. Rate (or speed) is how many cycles happen each second. On pitch, about 5 to 6 Hz sounds like a singer’s vibrato; on a pad’s filter, 0.1 Hz gives one slow sweep every ten seconds. Depth (or amount) is how far the target travels on each cycle. Many synths can sync the rate to tempo as a note value, so a wobble stays locked to the beat: one cycle per eighth note at 120 BPM is 4 Hz. The LFO’s shape matters too. A sine or triangle glides back and forth, a square flips between two values, a saw ramps and jumps back, and a random shape (often called sample and hold) jumps to a new value each cycle.
The difference from an envelope is timing. An envelope runs once per note, while an LFO keeps cycling for as long as the sound plays.
In Gelato Synth, the LFO page has one LFO with a target (pitch, filter, FM, shape or volume), a shape, a speed and an amount. What an LFO does on a synth has settings for vibrato, tremolo and wobble bass, and how synthesizers work shows where the LFO sits next to the envelopes.
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