SAMPLED

Synthesis and sound design · updated 2026-08-16

PULSE WIDTH MODULATION

Sweeping the duty cycle of a square wave. The harmonic content shifts as it moves, which is why one oscillator can sound like two.

Close-up of a Eurorack modular synthesizer: oscillator, filter and envelope modules wired together with patch cables, showing the signal path these synthesis terms describe.
Synthesis and sound design — Close-up of a Eurorack modular synthesizer: oscillator, filter and envelope modules wired together with patch cables, showing the signal path these synthesis terms describe.

Photo: Eurorack Modular Synthesizer Closeup (opens in a new tab) by Nir Yaniv (opens in a new tab), via Wikimedia Commons — CC BY-SA 4.0 (opens in a new tab)

Key takeaways

  • Sweeping the duty cycle of a square wave.
  • The harmonic content shifts as it moves, which is why one oscillator can sound like two.
  • Modulating that width slowly with an LFO produces the shimmering motion characteristic of vintage string and pad sounds.
  • One oscillator, a slow LFO on pulse width, a slight chorus — that is a Juno-style pad in three steps.
  • Watch out: setting pulse width at an extreme and leaving it there.

Quick checklist

  • Can you define pulse width modulation in one sentence without looking?
  • Can you point at pulse width modulation in a real session, mix or contract?
  • Have you tried the practical move above at least once?
  • Would you catch the common mistake before it costs you a take?
  • Have you opened one of the primary sources below rather than a forum thread?

PULSE WIDTH MODULATION IN DEPTH

Pulse width sets the duty cycle of a square wave, changing its harmonic content from hollow and nasal at extreme settings to full at 50%. Modulating that width slowly with an LFO produces the shimmering motion characteristic of vintage string and pad sounds.

How it works in practice

One oscillator, a slow LFO on pulse width, a slight chorus — that is a Juno-style pad in three steps.

The mistake people make

Setting pulse width at an extreme and leaving it there. Static narrow pulses read as thin; the motion is the point.

WHERE PULSE WIDTH MODULATION SITS

Pulse width modulation belongs to synthesis and sound design in the Sampled music glossary. How synths make sound, in the order the signal actually travels.

TEST YOURSELF

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3 quick questions on pulse width modulation. Answers are marked instantly — nothing is sent anywhere.

  1. 1. Which statement best describes pulse width modulation?

  2. 2. What is the mistake people most often make with pulse width modulation?

  3. 3. In practice, which of these applies to pulse width modulation?

Ready for the full thing? Take the 25-question terminology test and get a certificate with your name and score.

SOURCES AND CITATIONS

Free, primary references for pulse width modulation — standards bodies, manufacturers, government offices and university course material. Each one lists the line of this entry it backs up.

  • Stanford CCRMA — DSP texts (opens in a new tab)

    University research centre · Stanford CCRMA

    “Sweeping the duty cycle of a square wave.”— the claim this source supports

    Why it counts: The CCRMA course material derives this from first principles, so you can check the maths behind the plain-English version above.

  • Open Music Theory (opens in a new tab)

    Open textbook · Open Music Theory

    “The harmonic content shifts as it moves, which is why one oscillator can sound like two.”— the claim this source supports

    Why it counts: An openly licensed university textbook, so the definition can be checked against a citable academic source.

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