Carrier

In modulation-based synthesis such as FM, oscillators take on two roles, and the carrier is the one you actually hear. Its pitch tracks the notes you play and sets the fundamental of the sound, while a second oscillator, the modulator, is applied to it to reshape its tone. In frequency modulation the modulator rapidly varies the carrier's frequency, generating new harmonics called sidebands whose spacing and intensity depend on the frequency ratio between the two oscillators and the amount of modulation. The carrier-to-modulator ratio is the central creative control: simple whole-number ratios yield harmonic, musical tones like electric pianos and bells, while non-integer ratios produce clangorous, metallic timbres well suited to percussion.