History
The technique of the digital implementation of frequency modulation, which was developed by John Chowning (Chowning 1973, cited in Dodge and Jerse, p. 115) at Stanford University in 1967-68, was patented in 1975 and later licensed to Yamaha.
The implementation commercialized by Yamaha (US Patent 4018121 Apr 1977 or U.S. Patent 4,018,121) is actually based on phase modulation.
FM synthesis can create both harmonic and inharmonic sounds. FM synthesis using analog oscillators may result in pitch instability, but FM synthesis (using the frequency stable phase modulation variant) can be implemented digitally. As a result, FM synthesis was the basis of some of the early generations of digital synthesizers from Yamaha, with Yamaha's flagship DX7 synthesizer being ubiquitous throughout the 1980s. Yamaha had patented its hardware implementation of FM, allowing it to nearly monopolize the market for that technology. Casio developed a related form of synthesis called phase distortion synthesis, used in its CZ series of synthesizers. It had a similar (but slightly differently derived) sound quality to the DX series.
Don Buchla implemented FM on his instruments in the mid-1960s, prior to Yamaha's patent. His 158, 258 and 259 dual oscillator modules had a specific FM control voltage input, and the model 208 (Music Easel) had a modulation oscillator hard-wired to allow FM as well as AM of the primary oscillator. These early applications used analog oscillators.
With the expiration of the Stanford University FM patent in 1995, digital FM synthesis is now part of the synthesis repertoire of most modern digital synthesizers, usually in conjunction with additive, subtractive and sometimes sampling techniques. The FM synthesis patent brought Stanford $20 million dollars before it expired, making it (in 1994) "the second most lucrative licensing agreement in Stanford's history".
Stanford University are currently working on a new FMHD synthesis protocol with improved sound generation properties, and a real-time property modelling editor, that allows the user to encapsulate Karplus-Strong and other physical modelling aspects with relative ease.
Read more about this topic: Frequency Modulation Synthesis
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