Editing Frequency modulation synthesis (section)

==== Free use of FM after the patent expiration ====
With the expiration of the Stanford University FM patent in 1995, digital FM synthesis can now be implemented freely by other manufacturers. The FM synthesis patent brought Stanford $20&nbsp;million before it expired, making it (in 1994) "the second most lucrative licensing agreement in Stanford's history".<ref>Stanford University News Service (06/07/94), [http://news.stanford.edu/pr/94/940607Arc4222.html Music synthesis approaches sound quality of real instruments]</ref>

Today, FM is mostly found in software-based synths such as [[Native Instruments]]' FM8 or [[Image-Line]]'s [[Sytrus]] plug-ins, but it has also been incorporated into the synthesis repertoire of some modern digital synthesizers, usually coexisting as an option alongside other methods of synthesis such as [[subtractive synthesis|subtractive]], [[sample-based synthesis]], [[additive synthesis]], and other techniques. The degree of complexity of the FM in such hardware synths may vary from simple 2-operator FM, to the highly flexible 6-operator engines of the [[Korg Kronos]] and [[Alesis Fusion]], to creation of FM in extensively modular engines such as those in the latest synthesisers by [[Kurzweil Music Systems]].{{Citation needed|date=July 2019}}