The principles of beat frequency or heterodyning oscillators were discovered by chance during the first decades of the twentieth century by radio engineers experimenting with radio vacuum tubes. Heterodyning effect 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 (approximately 20 Hz to 20,000 Hz). the musical potential of the effect was noted by several engineers and designers including Maurice Martenot, Nikolay Obukhov, Armand Givelet and Leon (or Lev) Sergeivitch Termen the 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 and finally freeing the performer from the keyboard and fixed intonation.

Termen’s first machine, built in the USSR in 1917 was christened the “Theremin” (after himself) or the “Aetherophone” (sound from the ‘ether’) and was the first instrument to exploit the heterodyning principle. The original Theremin used a foot pedal to control the volume and a switch mechanism to alter the pitch. This prototype evolved into a production model Theremin in 1920, this was a unique design, resembling a gramaphone cabinet on 4 legs with a protruding metal antenae and a metal loop. The instrument was played by moving the hands around the metal loop for volume and around the antenae for pitch. The output was a monophonic continuous tone modulated by the performer. The timbre of the instrument was fixed and resembled a violin string sound. The sound was produced directly by the heterodyning combination of two radio-frequency oscillators: one operating at a fixed frequency of 170,000 Hz, the other with a variable frequency between 168,000 and 170,000 Hz. the frequency of the second oscillator being determined by the proximity of the musician’s hand to the pitch antenna. The difference of the fixed and variable radio frequencies results in an audible beat frequency between 0 and 2,000 Hz. The audible sound came from the oscillators, later models adding an amplifier and large triangular loudspeaker. This Theremin model was first shown to the public at the Moscow Industrial Fair in 1920 and was witnessed by Lenin who requested lessons on the instrument. Lenin later commissioned 600 models of the Theremin to be built and toured around the Soviet Union.

Lev Sergeivitch Termen playing the “Theremin”

Termen left the Soviet Union in 1927 for the United States where he was granted a patent for the Theremin in 1928. The Theremin was marketed and distributed in the USA by RCA during the 1930’s and continues, in a transistorised form, to be manufactured by Robert Moog’s ‘Big Briar’company.

The heterodyning vacuum tube oscillator became the standard method of producing electronic sound until the advent of the transistor in the 1960’s and was widely used by electronic musical instrument designs of the period. The Theremin became known in the USA as a home instrument and featured in many film soundtracks of the 1940-50’s, it also appeared in several pop records of the 1960’s but never overcame it’s novelty appeal and was used for effect rather than a ‘serious instrument’, most recordings employ the Theremin as a substitute string instrument rather than exploiting the microtonal and pitch characteristics of the instrument. Leon Sergeivitch Termen went on to develop variations on the original Theremin which included the “Terpsitone”, The “Rhythmicon”, the “keyboard Theremin” and the “Electronic Cello”.The “Keyboard Theremin”(1930)