However, the RCA Mark II Sound Synthesizer in 1957 was still indirectly controlled via punch-tape system similar to piano rolls, a kind of mechanical sequencer.
Also, in earlier electronic music, artists used sound-on-film technology to generate sound waves as well as control sequences of notes.
To avoid the monotony of endlessly repeated sequences, pioneering electronic musicians like Chris Franke of Tangerine Dream and Michael Hoenig would manipulate these switches in real time during performance, adding and dropping notes and beats from a sequence.
Good examples of all these techniques can be heard on the Phaedra, Rubycon, Ricochet, and Encore albums of Tangerine Dream, as well as on Departure from the Northern Wasteland by Michael Hoenig.
By synchronizing two sequencers, and manipulating them individually, swirling polyrhythmic phasing patterns (as introduced in minimalist music by Steve Reich) can be set up.
It's easily identified by its vertical column of 8 square white buttons that light up to indicate the active step(s).