Stockhausen. Silver Apples. Forbidden Planet. Before the development of what we think of as synthesizers, there was test and measurement equipment. Raw oscillators, filters and amplifiers intended for not musical but industrial purposes. At some point, experimental musicians realised that if you amplified the electric signals they put out, you could generate, process, and control audio signals.
It was Bob Moog and Don Buchla who took these raw building blocks and added musical control, and the rest is history. But for a certain subset of musicians, this original equipment is very much not history; it still holds plenty of potential for sonic experimentation.
