Way back in the early 1920s, when Léon Theremin worked at the Physico-Technical Institute in St. Petersburg, Russia, he noticed that when he moved his body in or out of an electromagnetic field produced by a radio frequency oscillating circuit, he changed its frequency [source: Harrison]. The human body has a certain natural capacitance (the ability to hold an electrical charge). What Theremin observed when he used his body to disrupt the oscillator’s electromagnetic field was the effect of this capacitance. Maybe because he was a musician and a cellist by hobby, Theremin began pondering how to exploit capacitance to create a new musical instrument.
In a 1989 interview with Olivia Mattis, Theremin said, "I conceived of an instrument that would create sound without using any mechanical energy, like the conductor of an orchestra" [source: Mattis]. What Theremin dreamed up was an electronic instrument with two primary circuits: a pitch circuit and a volume circuit. The pitch circuit used two tuned (radio frequency) oscillators: a fixed oscillator and a variable oscillator. The fixed oscillator generated waves at a static frequency. The variable oscillator was capable of producing a range of frequencies and was connected to a vertical antenna. Through a process called heterodyning, signals from the fixed and variable oscillators were mixed together. The frequency of one oscillator was subtracted from the other. The difference was amplified and, finally, output as an audible musical tone.
The second circuit (the volume circuit) controlled the level of the tone generated by the pitch circuit. Much like in the pitch circuit, it used an oscillator connected to an antenna. Disrupting the electromagnetic field around this antenna raises or lowered the volume of the music tone generated by the pitch circuit.
Today, hackers and musical tinkerers of all kinds use these same principles to create all manner of Theremins and Theremin-like devices. Since a simple fluttering of fingers is all it takes to make noise on a Theremin, it seems like the Theremin would be a cinch to play. Find out why many enthusiasts consider the Theremin the world's most difficult instrument in the next section.