(The information gathered below is courtesy of wikipedia)The theremin is one of the earliest electronic instruments, and was invented by Russian inventor Leon Theremin in 1919. On the left is an image of Theremin himself playing his instrument.
The instrument is composed of 2 radio frequency oscillators and 2 metal antennae, one controlling the frequency (pitch) and the other controlling the amplitude (volume). The electronic signals are fed into an amplifier, completing the instrument. Of note, this is the first musical instrument where the performer does not physically touch the instrument. The distance between the performer's hands and the antennae control the pitch and volume. The sound quality of the theremin is eerie and alien-like.
The theremin operates on the heterodyne principle. The instrument uses 2 radio frequency oscillators, one emitting a fixed frequency, and the other a variable frequency. The circuitry of the instrument is such that the performer's (right) hand acts as ground of a variable capacitor in an LC circuit. The variable frequency generated by the performer is mixed with the fixed frequency emitted by one of the frequency oscillators to generate a beat frequency which is in the audible range. This signal is then fed to the amplifier.
Volume control is accomplished with the performer's (left) hand acting as ground for another variable capacitor, which takes the place of a variable resistor usually used to control volume in audio equipment.
