Low-Frequency Oscillator

A slow oscillator makes no sound of its own, yet keeps the timbre in motion.

Related

ModulationTimbreMoog modular synthesizerModern

The question

A low-frequency oscillator makes no sound, yet almost every synth gives it a knob. What does it do, and why does slow motion bring a timbre alive?

How it works

An LFO runs below audio, usually from a fraction of a hertz to twenty hertz. It never reaches the ear directly; it pushes another parameter. To pitch it is vibrato, to level tremolo, to cutoff a wobble, to pan movement, to pulse width PWM. Rate sets speed, depth sets amount, and shape decides whether motion is smooth, stepped or random. A fade-in delay lets a long note settle first.

Settings and what you hear

Zero point one to two hertz suits slow drift and breathing. Four to seven hertz approaches the vibrato of a voice or a violin. Tempo-synced quarters or eighths give a rhythmic sway. A small depth is barely there, a large one exaggerated. Sine feels natural, square steps, and random shapes unsettle.

What to listen for

Hear a sustained pad and ask whether the tone is opening and closing rather than the level rising and falling. Then hear long strings and decide whether the wobble is pitch or level. Finally raise the rate from 0.3 Hz to 6 Hz and hear it turn from breath to tension to obvious vibrato.

Common misconceptions

That an LFO means vibrato, when it can push level, filter and pan; that faster is more expressive, when too fast only creates tension; that an LFO cannot change pitch, when pitch modulation is vibrato.

Sources

• Gordon Reid, Sound On Sound Synth Secrets — LFO routing checked, not quoted
• Curtis Roads, The Computer Music Tutorial — low-frequency modulation checked, not quoted

Used for fact-checking only; all prose is original.