As recounted in IEEE Spectrum’s March 1985 design case history [PDF]of the C64 by Tekla S. Perry and Paul Wallich, MOS originally intended just to make a new graphics chip and a new sound chip. The idea was to sell them as components to microcomputer manufacturers. But those chips turned out to be so good that MOS decided to make its own computer.
Creation of the sound chip fell to a young engineer called Robert Yannes. He was the perfect choice for the job, motivated by a long-standing interest in electronic sound. Although there were some advanced microcomputer-controlled synthesizers available, including the Super Sound board designed for use with the Cosmac VIP system, the built-in sound generation tech in home computers was relatively crude. Yannes had higher ambitions. “I’d worked with synthesizers, and I wanted a chip that was a music synthesizer,” Yannes told Spectrum in 1985. His big advantage was that MOS had a manufacturing fab on-site. This allowed for cheap and fast experimentation and testing: “The actual design only took about four or five months,” said Yannes.