LFOs & Modulation

An envelope moves a sound once per note. But lots of musical motion is cyclic: a singer's vibrato, a surf-guitar throb, a dubstep wobble. For that, synths use a second oscillator that runs too slowly to hear (usually under 20 Hz) and is never sent to the speakers. Instead, its slow wave is wired to another control and wiggles it automatically. It's called a Low Frequency Oscillator, LFO.

An LFO only has three questions to answer:

• Rate: how fast it cycles (0.1 Hz slow sweep → 20 Hz rough flutter).
• Depth: how far it pushes the destination.
• Destination: which knob is it turning for you? This is the big one.

Same LFO, three destinations, three completely different effects. Power on and flip between them:

• LFO → Pitch = vibrato. The note wavers around its center.
• LFO → Volume = tremolo. Loudness pulses; pitch stays put.
• LFO → Filter = wobble. Brightness pumps, slow it to ~0.5 Hz for a cinematic sweep, or ~4 Hz with depth cranked for the bass-music wub.