Phase Modulation (PM) synthesis is another type of synthesis via signal modulation. As in Frequency Modulation (FM), a carrier wave is modulated by another oscillator. If in FM the frequency of the carrier vawe is driven by the amplitude of the driver wave, in PM the phase of the carrier wave is driven by the amplitude of the driver wave. This means that the  waveform of the carrier signal is shifted forwards or backwards in time in response to the modulating signal. As the phase of the carrier waveform changes, the resulting sound can exhibit various forms of spectral complexity, including harmonically rich or inharmonic timbres. PM synthesis is often used to create metallic sounds, plucked string instruments, and other sounds that require a percussive or transient character.

Both techniques allows to synthesis a wide range of sound. In practice, by assuming the carrier wave is a sinusoidal function, PM is more efficient than FM with respect to computationoal complexity, and it requires fewer parameters to control. In FM synthesis, the ratio between the modulating frequency and carrier frequency must be carefully adjusted to create a specific sound. In contrast, PM synthesis only requires the modulation index to be adjusted. This makes it easier to use for sound designers and musicians who may not have a deep understanding of the complex math involved in FM synthesis.
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