Frequency Modulation synthesizers use the same technology as FM radio to produce sound. They are considered much more complex to program than subtractive synthesis Instead of using oscillators and LFOs as in subtractive synthesis, an FM synthesizer uses multiple operators. The primary difference between operators and oscillators is in the way they are used. In the case of the Yamaha DX series, the operators used are simple sine waves. At a basic level, an operator called a carrier serves as the sound source for the synthesizer. An operator called a modulator functions like an LFO to modulate the signal of the carrier. Unlike an LFO, a modulator oscillates at a very high frequency; higher than the frequency of the carrier. At harmonic intervals (frequency multiples of 2) the modulation signal produces changes in the timbre (quality of sound) of the carrier. Using multiples operators creates even more complex sounds.
