MOS Technology SID

The MOS Technology 6581/8580 SID (Sound Interface Device) is the built-in Programmable Sound Generator chip of Commodore's CBM-II, Commodore 64, Commodore 128 and Commodore MAX Machine home computers. It was one of the first sound chips of its kind to be included in a home computer prior to the digital sound revolution.

Together with the VIC-II graphics chip, the SID was instrumental in making the C64 the best-selling computer in history, and is partly credited for initiating the demoscene.

The SID has U.S. Patent 4,677,890, which was filed on February 27, 1983, and issued on July 7, 1987. The patent expired on July 7, 2004.

The SID was devised by engineer Robert "Bob" Yannes, who later co-founded the Ensoniq digital synthesizer company. Yannes headed a team that included himself, two technicians and a CAD operator, who designed and completed the chip in five months, in the latter half of 1981. Yannes was inspired by previous work in the synthesizer industry and was not impressed by the current state of computer sound chips. Instead, he wanted a high-quality instrument chip, which is the reason why the SID has features like the envelope generator, previously not found in home computer sound chips.

I thought the sound chips on the market, including those in the Atari computers, were primitive and obviously had been designed by people who knew nothing about music.

Emphasis during chip design was on high-precision frequency control, and the SID was originally designed to have 32 independent voices, sharing a common oscillator. However these features could not be finished in time, so instead the mask work for a certain working oscillator was simply replicated three times across the chip's surface, creating three voices each with its own oscillator. Another feature that was not incorporated in the final design was a frequency look-up table for the most common musical notes, a feature that was dropped because of space limitations. The support for an audio input pin was a feature Yannes added without asking, which in theory would have allowed the chip to be used as a simple effect processor. The masks were produced in 7-micrometer technology to gain a high yield; the state of the art at the time was 6-micrometer technologies.

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