The principles of beat frequency (or heterodyning oscillators) were discovered by chance during the first decades of the 20th century by radio engineers experimenting with radio vacuum tubes. Heterodyning is created by two high radio-frequency sound waves of similar but varying frequency combining and creating a lower audible frequency, equal to the difference between the two radio frequencies.
The musical potential of the effect was noted by several engineers and designers including Leon (or Lev) Sergeivitch Termen, a Russian cellist and electronic engineer. One problem with utilising the heterodyning effect for musical purposes was that, as the body came near the vacuum tubes, the capacitance of the body caused variations in frequency. Leon Termen realised that, rather than being a problem, body capacitance could be used as a control mechanism for an instrument.
The Frenchman Maurice Martenot, also a cellist as well as a radio telegrapher, met Leon Termen in 1923. This meeting lead Martenot to develop a new instrument based on Termen's ideas. The first model of what was to become known as the ondes Martenot was patented on 2 April 1928 under the name Perfectionnements aux instruments de musique électriques (improvements to electronic music instruments). Martenot's aim was to produce a versatile electronic instrument that was immediately familiar to orchestral musicians.
The first versions bore little resemblance to the later production models: consisting of two table-mounted units controlled by a performer who manipulated a string attached to a finger ring (using the body's capacitance to control the sound characteristics in a manner very similar to the Theremin); this device was later incorporated as a fingerboard strip above the keyboard. Later versions used a standard keyboard.
The ondes Martenot's success was the Theramin's loss - although both used the vacuum tube oscillator as a sound source and were both monophonic, where the Theremin had a sliding scale and no fixed preset notes, the ondes Martenot had a keyboard and a strip control for glissando and vibrato, and an appearance that was familiar to any keyboard player. The instrument also had a bank of expression keys that allowed the player to change the timbre and character of the sounds. A later (1938) version of the instrument featured microtonal tuning as specified by the Hindu poet Rabindranath Tagore and the musician Alain Danielou.
The ondes Martenot was quickly accepted and a wide repertoire of works were written for the instrument, not only by Olivier Messiaen but also by composers such as Edgard Varèse, Darius Milhaud, Arthur Honegger, Maurice Jarre, André Jolivet and Charles Koechlin. 20 years after its invention, Martenot himself became a professor at the Paris Conservatoire, where he taught the ondes Martenot.
Drawn from articles by Simon Crab from 120 Years of Electronic Music, an ongoing web project. For further information and images, visit: www.obsolete.com/120_years/machines/martenot