What Is Phase Modulation?

Phase Modulation (PM) is a synthesis technique where one signal modulates the phase of another oscillator — rather than its frequency. To your ears, it can sound very similar to Frequency Modulation (FM), especially at audio rates.

In practice, PM is most commonly found in digital synths and software because it’s easier to implement and keeps tuning more stable than traditional FM. That makes it great for clean, controllable harmonic content — or extreme metallic chaos if you want it.

PM vs FM

• FM: Modulates frequency directly. Can create tuning drift or instability, especially in analog gear.
• PM: Modulates phase, but produces similar harmonic results — typically with better tracking in digital systems.
• At audio rates, both techniques can sound almost identical.

Phase Distortion (Casio CZ style)

Casio’s CZ-series synths took a different approach called Phase Distortion (PD). Instead of using a second oscillator for modulation, PD warps the internal phase of a waveform using a lookup table or curve — reshaping time itself inside the oscillator.

This technique lets a sine wave behave like a saw, square, or other complex waveform, depending on the distortion curve. It’s not technically FM or PM, but it lands in the same sonic ballpark with a totally different internal mechanism.

PM vs PD

• Phase Modulation: Uses one oscillator to modulate another’s phase.
• Phase Distortion: Warps the shape of a waveform’s phase curve internally — no external modulator needed.

The result? Both techniques create rich, evolving harmonics — but PD is shape-based, while PM is modulator-based. If you’ve ever played a CZ-series synth, that squishy, rubbery digital timbre is pure PD magic.

Patch Tips

• In PM, use sine waves for clean harmonic tones — then try modulating with more complex shapes.
• Try chaining multiple PM stages for wild overtones and motion.
• Explore envelope-based PM depth for pluck, growl, or formant-like animation.
• In software, find PD-style waveforms for easy Casio-inspired patches without extra oscillators.

PM and PD are both tools for carving complex sounds from simple ingredients. Whether you're patching audio-rate PM in modular or shaping time curves digitally, these techniques are where digital synthesis gets fun.