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234 Chapter 22 ES2
Linear Frequency Modulation
The principle of linear frequency modulation (FM) synthesis was developed in the late
sixties and early seventies by John Chowning. It’s such a flexible and powerful method
of tone generation that synthesizers were developed, based solely on the idea of FM
synthesis. The most popular FM synthesizer ever built is Yamaha’s DX7. FM synthesis is
also found in other models of the Yamaha DX range and some Yamaha E-Pianos. In the
discipline of pure FM synthesis, the ES2 can’t be compared with these synthesizers, but
it can certainly achieve some of their signature sounds.
Note: The DX7 featured six oscillators (called operators) per voice, with each controlled
by a separate envelope generator. It’s bell-like, synthetic electric piano sounds became
de rigeur in popular music, especially in soul ballads (Whitney Houston and others).
Between the Sine setting (when the sine symbol is selected) and the FM symbol of the
Oscillator 1 knob, a range is available which allows stepless control over the amount of
frequency modulation. This parameter is also available as a modulation address.
Note: Osc1Wave is optimized for subtle FM sounds, utilizing lower FM intensity
amounts. For more extreme FM modulations, the Router offers the Osc1WaveB target.
See the “Modulation Targets”, on page 254.
The frequency of Oscillator 1 can be modulated by the output signal of Oscillator 2.
Whenever it outputs a positive voltage, the frequency of Oscillator 1 will increase.
Whenever it is negative, its frequency will decrease.
The effect is similar to an LFO modulation, being used to create a vibrato (a periodic
modulation of the frequency) or a slow siren effect. In comparison to an LFO, Oscillator
2 does not oscillate slowly. In the audio domain, it oscillates a little faster than Oscillator
1 itself. Thus, Oscillator 1’s oscillation also accelerates and slows down within a single
phase, resulting in a distortion of the basic sine shape of Oscillator 1. This sine wave
distortion has the side benefit of a number of new harmonics becoming audible.