• Info
• History of FM
• Sound Basics
• FM & Vibrato
• Unit Generators
• Simple FM Theory
• Modeling Timbres
• Amplitude Envelope
• FM Parameters
• Bibliography
• Acknowledgements
• Future Bessie

SIMPLE FM THEORY

Schematic Diagram: Simple FM

The diagram at the right is a schematic representation of SIMPLE FM. As you can see, simple FM involves only two unit generators (or operators for those who remember Yamaha DX7 jargon). Each unit generator generates a sinewave.

The only variables essential for simple FM are: F(c) (frequency of the carrier waveform) F(m): (frequency of the modulator waveform) and Index: percentage of delta F as related to F(m) .

(It turns out that it's easier to track delta F as it relates to the Modulator Frequency. By dividing delta F by F(m), we arrive at a ratio value which is easier to understand, remember and predict the results of for FM synthesis.) Increasing the Index will generate a sound with more frequencies in it (a ‘wider’ spectral bandwidth). Notice that as you increase the Index, sounds appear both on the high end and on the low end of the sound… the total musical tone color, or timbre, is easily changed by changing the Index. An Index value of 0 (zero) will mean there’s no FM synthesis going on at all… so you hear only the sinewave of the carrier unit generator (UG).

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