RMI began producing the 300 Series Electra-piano in 1967. As with earlier instruments, the Electra-piano featured an oscillator for each key. It uses an LC oscillator to generate the sound, as it produced a stable frequency that was not prone to drift. The signal is then run through a series of filters in order to produce an envelope resembling that of a piano. The Electra-piano also had an "organ mode" that allowed each note to sustain indefinitely instead of decay like a piano, and an "accenter" that added a percussion effect to the start of each note being played.