Pulse Width Modulation

What Is PWM?

PWM stands for Pulse Width Modulation. It’s a technique where the shape of a pulse wave is modulated over time – making the waveform narrower or wider without changing its frequency.

To the ear, this creates movement and animation. It’s a classic way to add life to a static square wave, and it’s a signature sound in subtractive synths, string machines, and vintage polysynths.

How It Works

  • A pulse wave is just a square wave with adjustable width – meaning how long it stays high vs low during each cycle.
  • At 50%, it’s a classic square wave. But if you shift the pulse width, it becomes asymmetrical and takes on a different harmonic profile.
  • By modulating that width with an LFO, envelope, or other CV source, you get a constantly shifting tone.

Why It Sounds So Good

Changing the pulse width affects the harmonic content of the waveform – subtly or dramatically. It’s like rotating the sound inside-out. This creates rich chorusing, wobble, and that “alive” feeling that analog synths are known for.

Common Use Cases

  • Static PWM: Manually dial in a sweet spot – sounds thicker than a plain square wave.
  • LFO into PWM: Classic animation. Great for pads, strings, and retro synth voices.
  • Envelope into PWM: Add expression – widen or narrow the wave as part of the sound’s shape.

Pro Tips

  • Don’t overdo modulation depth – subtle PWM often sounds more musical than extreme shifts.
  • Try PWM on multiple detuned oscillators – you get a thick, swirling character that rivals chorus FX.
  • Send PWM into a filter and modulate both for layered movement.

It’s a simple trick – but it makes a square wave come alive. PWM is one of those features that always feels worth it, whether you’re building fat basses, lush pads, or vintage leads.

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