Of two companies that in the mid-‘70s designed and sold analog integrated circuits used to design synthesizers (the other was Curtis Electromusic). SSM's origins are rather obscure and even its acronym stands for different things depending on what old documentation one looks at -- Solid State Music Technology, Solid State Microtechnolgy for Music, and Solid State Microelectronics have all been seen. The company originated out of a early-1970s informal group of Silicon Valley computer hobbyists who formed an organization called the Homebrew Computer Club. A number of personal computer manufacturers, including Apple, grew out of this club.
SSM's first products were computer boards for the now-obsolete S-100 bus standard, including some boards intended for music applications. As Dave Rossum told the story in a 1981 interview with Polyphony magazine, an engineer named Ron Dow had come to E-mu Systems looking for funding to develop a voltage controlled amplifier on a chip. However, the proposed design would not have been compatible with the modular synthesizers that E-mu was selling at the time, so they turned Dow down. Dow then went to SSM and they agreed to fund the project and market it. The result was the first synthesizer-specific integrated circuit, the SSM 2000 VCA. The following year, Dow came back with an idea for an improved design that eliminated E-mu's objections; at this point E-mu became involved with SSM in the design, and the result was the SSM 2010.
E-mu became both a co-creator and a customer for SSM's circuits, incorporating the ICs into their modulars; Rossum consulted with Dow and SSM on the designs. Shortly after, E-mu consulted with Oberheim on their first (non-SEM) polyphonic synth designs using the SSM ICs, but no Oberheim synths ever ended up using SSM chips. SSM chips were used in many late-‘70s and early-‘80s polyphonic analog synths, including the Korg models of the day, the Voyetra 8, and the rev 1 and 2 Prophet-5s. Connoisseurs of such things consider the SSM chips to produce a “thicker” and “ballsier” sound than the Curtis design, but the SSMs had some reliability problems and by 1985 most designers that were still specifying these types of ICs had switched to Curtis. SSM went through several changes of hands starting in the late 1980s. It is now a division of Analog Devices. Most of the classic SSM synth-specific designs are long out of production, but AD does still produce some of the VCA circuits and matched transistor arrays.