Synthesis FM

Patented by the engineer John Chowning in 1973 with CCRMA of Stanford, the synthesis FM is a sound process of synthesis which uses the Frequency modulation (FM for frequency modulation ). The patent was repurchased thereafter by Yamaha which used it in the synthetizer DX7. The principal interest of the synthesis FM is that with only two Oscillateur S, it makes it possible to generate a its container a great number of partial.

Mathematical expression

Let us consider the case of a sinusoid modulated in frequency by another sinsuoide. That is to say $f\_\; \{p\}$ the frequency of carrying, $f\_\; \{m\}$ the frequency of the modulating sinusoid and $I\_\; \{m\}$ the index of modulation. The output signal $y\; (T)$ is expressed in the form.

$y\; (T)\; =\; \backslash \; sin\; (2\; \backslash \; pi\; f\_\; \{p\}\; t+I\_\; \{m\}\; \backslash \; sin\; (2\; \backslash \; pi\; f\_\; \{m\}\; T))$

Advantages/Disadvantage

This synthesis can give very natural sounds (stories for example) and extremely varied. It has however as a disadvantage of being much more unstable than the additive sound Synthèse, in the sense that a light modification of a parameter of the modulation (carrier frequency, frequency of modulation or index of modulation) can change the distribution of the harmonics completely, or the stamp of its product. That can also be perceived as an advantage, because the synthesis FM can then be used to produce new sounds of synthesis.

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