In 1974, RMI produced the pioneering "Keyboard Computer" model keyboard instrument, the first portable digital sample player. It produced sounds from waveform model punch cards which were input and digitized into volatile memory, and used no magnetic tapes (in contrast to how Mellotron, Chamberlin, and Birotron created their sounds).
From 1974-76 RMI produced its only true synthesizer, the $3,000 RMI Harmonic Synthesizer,an instrument that was years ahead of its time (Yamaha's DX-7 was released in 1983, nine years later) but not widely used or understood. The 48-key dual mono, analog/digital hybrid synth featured two digital harmonic generators (16 harmonics each, with two sets of harmonic sliders), five presets, an LFO, arpeggiator, a VCF with mixable LP,BP and HP outputs, and AM and FM capability.
It was used most prominently by Jean Michel Jarre who played the RMI Harmonic Synthesizer on his Oxygène (1976) album as well as on many other albums that were to follow later. Stevie Wonder and Isaac Hayes were also rumoured to have this instrument in their rigs. In more recent times, the Harmonic Synthesizer was used by Richard D. James aka Aphex Twin and Stephen Parsick.
In 1979 RMI introduced the DK-20 (Digital Keyboard) as a replacement for the old analog 300 Series. This model was produced until 1982.