The theremin is an electronic musical instrument controlled without physical contact by the thereminist (performer).
It is named after its inventor, Léon Theremin, who patented the device in 1928.
The instrument’s controlling section usually consists of two metal antennas that sense the relative position of the thereminist’s hands and control oscillators for frequency with one hand and amplitude (volume) with the other. The electric signals from the theremin are amplified and sent to a loudspeaker.
The sound of the instrument is often associated with eerie situations. Thus, the theremin has been used in movie soundtracks such as Miklós Rózsa’s Spellbound and The Lost Weekend, Bernard Herrmann’s The Day the Earth Stood Still, and Justin Hurwitz’s First Man, as well as in theme songs for television shows such as the ITV drama Midsomer Murders.
The theremin is also used in concert music (especially avant-garde and 20th- and 21st-century new music), and in popular music genres such as rock.
The theremin was the product of Soviet government-sponsored research into proximity sensors. The instrument was invented by a young Russian physicist named Lev Sergeyevich Termen (known in the West as Léon Theremin) in October 1920 after the outbreak of the Russian Civil War.
After a lengthy tour of Europe, during which time he demonstrated his invention to packed houses, Theremin moved to the United States, where he patented his invention in 1928. Subsequently, Theremin granted commercial production rights to RCA.
Although the RCA Thereminvox (released immediately following the Stock Market Crash of 1929) was not a commercial success, it fascinated audiences in America and abroad. Clara Rockmore, a well-known thereminist, toured to wide acclaim, performing a classical repertoire in concert halls around the United States, often sharing the bill with Paul Robeson.
During the 1930s, Lucie Bigelow Rosen was also taken with the theremin and together with her husband Walter Bigelow Rosen provided both financial and artistic support to the development and popularisation of the instrument.
In 1938, Theremin left the United States, though the circumstances related to his departure are in dispute. Many accounts claim he was taken from his New York City apartment by NKVD agents (preceding the KGB), taken back to the Soviet Union, and made to work in a sharashka laboratory prison camp at Magadan, Siberia. He reappeared 30 years later.
In his 2000 biography of the inventor, Theremin: Ether Music and Espionage, Albert Glinsky suggested he had fled to escape crushing personal debts and was then caught up in Stalin’s political purges. In any case, Theremin did not return to the United States until 1991.
After a flurry of interest in America following the end of the Second World War, the theremin soon fell into disuse with serious musicians, mainly because newer electronic instruments were introduced that were easier to play.
However, a niche interest in the theremin persisted, mostly among electronics enthusiasts and kit-building hobbyists. One of these electronics enthusiasts, Robert Moog, began building theremins in the 1950s, while he was a high-school student. Moog subsequently published a number of articles about building theremins, and sold theremin kits that were intended to be assembled by the customer. Moog credited what he learned from the experience as leading directly to his groundbreaking synthesizer, the Moog.
Since the release of the film Theremin: An Electronic Odyssey in 1993, the instrument has enjoyed a resurgence in interest and has become more widely used by contemporary musicians. Even though many theremin sounds can be approximated on many modern synthesizers, some musicians continue to appreciate the expressiveness, novelty, and uniqueness of using an actual theremin. The film itself has garnered excellent reviews.
Both theremin instruments and kits are available. The Open Theremin, open hardware, and open software project were developed by swiss micro engineer Urz Gaudenz, using the original heterodyne oscillator architecture for an authentic playing experience, combined with Arduino. Using a few extra components a MIDI interface can be added to the Open Theremin, enabling a player to use their Theremin to control different instrument sounds.
Some inexpensive theremins may only have pitch control and may be harder to play accurately because of a relatively non-linear relationship between the distance of the hand and resultant pitch, as well as a relatively short span of hand-to-antenna distance for producing the available range of pitch.
The theremin is distinguished among musical instruments in that it is played without physical contact. The thereminist stands in front of the instrument and moves his or her hands in the proximity of two metal antennas.
The distance from one antenna determines frequency (pitch), and the distance from the other controls amplitude (volume). Higher notes are played by moving the hand closer to the pitch antenna. Louder notes are played by moving the hand away from the volume antenna.
Most frequently, the right-hand controls the pitch, and the left controls the volume, although some performers reverse this arrangement. Some low-cost theremins use a conventional, knob operated volume control and have only the pitch antenna. While commonly called antennas, they are not used for receiving or broadcasting radio waves but act as plates of capacitors.
The theremin uses the heterodyne principle to generate an audio signal. The instrument’s pitch circuitry includes two radio frequency oscillators set below 500 kHz to minimize radio interference. One oscillator operates at a fixed frequency. The frequency of the other oscillator is almost identical and is controlled by the performer’s distance from the pitch control antenna.
The performer’s hand acts as the grounded plate (the performer’s body being the connection to ground) of a variable capacitor in an L-C (inductance-capacitance) circuit, which is part of the oscillator and determines its frequency. In the simplest designs, the antenna is directly coupled to the tuned circuit of the oscillator, and the ‘pitch field‘, that is the change of note with distance, is highly nonlinear, as the capacitance change with distance is far greater near the antenna. In such systems, when the antenna is removed, the oscillator moves up in frequency.
To partly linearise the pitch field, the antenna may be wired in series with an inductor to form a series tuned circuit, resonating with the parallel combination of the antenna’s intrinsic capacitance and the capacitance of the player’s hand in proximity to the antenna.
This series tuned circuit is then connected in parallel with the parallel tuned circuit of the variable pitch oscillator. With the antenna circuit disconnected, the oscillator is tuned to a frequency slightly higher than the stand-alone resonant frequency of the antenna circuit.
At that frequency, the antenna and its linearization coil present an inductive impedance; and when connected, behaves as an inductor in parallel with the oscillator. Thus, connecting the antenna and linearising coil raises the oscillation frequency.
Close to the resonant frequency of the antenna circuit, the effective inductance is small, and the effect on the oscillator is greatest; farther from it, the effective inductance is larger, and fractional change on the oscillator is reduced.
When the hand is distant from the antenna, the resonant frequency of the antenna series circuit is at its highest; i.e., it is closest to the free-running frequency of the oscillator, and small changes in antenna capacitance have the greatest effect. Under this condition, the effective inductance in the tank circuit is at its minimum and the oscillation frequency is at its maximum.
The steepening rate of change of shunt impedance with hand position compensates for the reduced influence of the hand being further away. With careful tuning, a near-linear region of pitch field can be created over the central 2 or 3 octaves of operation. Using optimized pitch field linearisation, circuits can be made where a change in capacitance between the performer and the instrument in the order of 0.01 picofarads produces a full octave of frequency shift.
The mixer produces the audio-range difference between the frequencies of the two oscillators at each moment, which is the tone that is then wave-shaped and amplified and sent to a loudspeaker.
To control volume, the performer’s other hand acts as the grounded plate of another variable capacitor. As in the tone circuit, the distance between the performer’s hand and the volume control antenna determines the capacitance and hence natural resonant frequency of an LC circuit inductively coupled to another fixed LC oscillator circuit operating at a slightly higher resonant frequency. When a hand approaches the antenna, the natural frequency of that circuit is lowered by the extra capacitance, which detunes the oscillator and lowers its resonant plate current.
In the earliest theremins, the RF plate current of the oscillator is picked up by another winding and used to power the filament of another diode-connected triode, which thus acts as a variable conductance element changing the output amplitude.
The harmonic timbre of the output, not being a pure tone, was an important feature of the theremin. Theremin’s original design included audio frequency series/parallel LC formant filters as well as a 3-winding variable-saturation transformer to control or induce harmonics in the audio output.
Modern circuit designs often simplify this circuit and avoid the complexity of two heterodyne oscillators by having a single pitch oscillator, akin to the original theremin’s volume circuit.
This approach is usually less stable and cannot generate the low frequencies that a heterodyne oscillator can. Better designs (e.g., Moog, Theremax) may use two pairs of heterodyne oscillators, for both pitch and volume.