Modulation: Wobble Everything

A perfectly steady tone is boring. Nothing in nature holds perfectly still. Singers wobble their pitch slightly. Violinists rock their wrist on the string. Guitar amps from the 1950s had a literal pulsing light bulb inside that made the volume throb.

This wobbling is modulation: using one signal to control another. And the thing doing the controlling is an LFO - a Low Frequency Oscillator. It's an oscillator just like the one making your sound, except it's too slow to hear. Instead of making a tone, it makes a movement.

Enable LFO 1 below. Listen. Then enable LFO 2 on a different target and let them interfere with each other. Things get strange quickly.

Machine 6

Waveform

Pitch

Freq 261.6 Hz

261.6

Volume

Volume -5.8 dB

LFO 1

Target

Shape

Rate 5.3 Hz

Depth 30%

LFO 2

Target

Shape

Rate 5.0 Hz

Depth 30%

What does modulation look like?

A plain tone is a wave that never changes. Modulation means using a slow invisible wave (the LFO) to push and pull something about the audible wave. The two most common targets are amplitude (volume) and frequency (pitch).

No modulation

Steady amplitude, steady pitch. A test tone.

Amplitude modulation (tremolo)

Volume rises and falls. The wave swells and shrinks.

Frequency modulation (vibrato)

Pitch wobbles up and down. The wave squeezes and stretches.

Vibrato: wobbling the pitch

Singers do this naturally. Their vocal cords oscillate slightly above and below the target note. Violinists do it by rocking their wrist on the string. It adds warmth and expression.

A completely steady pitch sounds robotic. Even a tiny wobble makes it feel alive.

Try it: Set LFO 1 to target Pitch, sine wave, rate around 5 Hz, depth around 15%. That is classic vibrato.

Tremolo: wobbling the volume

The sound pulses louder and softer. Old Fender guitar amps had a circuit that did this - it literally varied the signal level using the glow of a light bulb hitting a photoresistor. The faster the bulb pulsed, the faster the tremolo.

Fender labelled the tremolo effect on their amps as "vibrato" and the vibrato arm on their guitars as "tremolo bar." Both wrong. They have known about this for decades and never fixed it. The entire guitar industry now uses the wrong words because of one company's label printer in 1956.

LFO waveform shapes

Sine gives smooth, organic wobble - the most natural sounding. Square snaps between two values with no in-between, like a switch being flicked. Sawtooth ramps in one direction then snaps back. Triangle is like sine but with sharper corners, a bit more mechanical.

Layering two LFOs

Natural vibrato is never a perfect sine wave. It is messy. The messiness is the beauty.

Try it: Set both LFOs to target Pitch, one at 3 Hz and one at 7 Hz, both sine, moderate depth. The two wobbles interfere and create complex, unpredictable-feeling movement.

Into FM synthesis territory

When the LFO rate gets fast enough, modulation stops being "expression" and starts creating entirely new timbres. The pitch moves so rapidly it fuses into a different kind of sound - a texture, a buzz, almost a new instrument.

Try it: Crank LFO 1 depth to 100% and rate to maximum. This is FM synthesis territory. The Yamaha DX7 worked this way. Every phone ringtone from 1998 to 2005 was generated like this.

Why it matters

Modulation is the secret to making synthesisers sound alive. A static waveform at a fixed frequency is a test tone. Add a little wobble and suddenly it breathes.

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