Operators are the primary sources of sound for the [fm-synth]. Usually, each operator is an oscillator that produces sound just like a [traditional-oscillator-based-synthesizer]. However, the basis of FM synthesis comes from the fact that operators modulate the frequency of other operators. By configuring the amounts and routing of operators' modulation via the [modulation-matrix] and varying the amounts of modulation over time, a huge variety of different sounds and timbres can be produced.