Modulator

The modulator is the counterpart to the carrier in modulation-based synthesis. Rather than being heard on its own, it is applied to the carrier to reshape its sound. In frequency modulation, the modulator's output rapidly varies the carrier's frequency; the speed of that variation depends on the modulator's pitch and the intensity on its level, and together they determine which new harmonics, or sidebands, appear. Raising the modulator's level generally adds more and brighter harmonics, which is why an envelope on modulator amount produces the evolving brightness characteristic of FM electric pianos and bells. A modulator can itself be driven by yet another oscillator, and chaining several this way is how complex FM instruments build their intricate, animated timbres.