Amplitude Modulation

What Is Amplitude Modulation?

Amplitude Modulation (AM) is when the **loudness** (amplitude) of a signal is modulated by another signal. That modulator could be slow, like an LFO, or fast, like another oscillator.

The result can range from a soft tremolo to totally new waveforms with strange harmonics and motion. You’re not changing the pitch – you’re shaping how much of the sound you hear, and how fast it changes.

How It Works

  • A VCA is used to control the amplitude of a sound source (like an oscillator).
  • You patch a second signal into the VCA’s control input – that’s the modulator.
  • The result: the main signal gets louder and quieter at the rate and shape of the modulator.

The Ambulance Analogy

Note: I saw this in a video and found it really helpful for understanding, I havent been able to find it since, If you do, please send me an email, I’d love to credit and link to it here.

Think of an ambulance driving past. The siren doesn’t change pitch right away – but it seems louder as it approaches, and quieter as it drives away. That shifting volume shape is the heart of AM – the change in distance is like the modulating signal, warping the amplitude of the sound over time.

Low-Rate vs Audio-Rate AM

  • Low-rate AM (LFO): Think tremolo – a slow pulsing or wobble in volume.
  • Audio-rate AM: Produces new frequencies – often metallic, complex, or hollow. Especially interesting when using non-sine waveforms.

AM vs FM

  • AM: Modulates volume – the shape of the loudness.
  • FM: Modulates pitch – the shape of the frequency itself.

AM often sounds cleaner and more controlled than FM. It’s great for dynamic textures and rhythmic motion, or weird digital harmonics when used at high speeds.

Patch Tips

  • Use an LFO into a VCA to create classic tremolo – triangle and sine work well.
  • Try an oscillator modulating another oscillator’s VCA for rich, growling motion.
  • Use envelopes as modulators for amplitude shaping over time (this is technically AM too).
  • Experiment with ring modulators – they’re a form of AM with a twist (typically no carrier signal bleed).

AM is one of the simplest ways to bring your patches to life – and one of the easiest to explore. Whether you’re pulsing a pad or sculpting alien timbres, it’s a key tool in the modulation toolkit.

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