A manufacturer of electronic instruments in the late '60s and '70s. RMI stood for "Rocky Mount Instruments" after its location in Rocky Mount, North Carolina USA. It was owned by the venerable Allen Organ Company and was originally opened as an R&D office.
Their best known product was their line of electric pianos and related instruments, which unlike competing products from Rhodes, Wurlitzer, and Hohner, were fully electronic. The pianos were fully polyphonic, with a voice circuit for each key consisting of a fixed-frequency oscillator, an envelope generator and a VCA. Fixed filter circuits provided a small set of timbres including piano, harpsichord, and guitar/lute sounds, which could be selected in any combination.
The intriguing feature of the pianos (known as Electra-Pianos, with some models being denoted as Rock-Si-Chords) was the "organ mode", in which the envelope release time was changed to a very long value. Progressive rock keyboardists in the '70s found that this was ideal for running through distortion and phaser effects to produce very un-pianolike sounds. The model 368 was a favorite of Tony Banks who had his modified with built-in effects.
RMI manufactured several digital synthesizers that were ahead of their time. The Keyboard Computer I and II models were basically early digital wavetable synthesizers which contained multiple 1/2-cycle samples that could be selected via front panel switches; additional waveforms could be fed in via a punch-card reader on the front panel, with pre-programmed cards being available from dealers. The Harmonic Synthesizer contained two additive waveform generators that were each capable of 16 harmonics, and the mix was completely controllable via banks of sliders on the panel. Unfortunately, the Harmonic Synthesizer was so different from contemporary products that performers couldn't figure out what to do with it, and RMI's marketing was minimal, so few were sold. Jean-Michel Jarre used a Harmonic Synthesizer extensively on his early albums. That being said, the Keyboard Computer models achieved mild success, being used by Todd Rundgren, Rick Wakeman, and a few others.
RMI ceased operations in 1982 as its piano and combo organ products were supplanted by the more advanced polyphonic synths that appeared in the late '70s. The parent company, Allen Organ, is still in business and has been a pioneer in incorporating digital circuitry into large church and theater organs, based in part on work done by RMI.