Theremin
The theremin is an electronic musical instrument controlled without physical contact by the performer. It is named after its inventor, Leon Theremin, who patented the device in 1928.
The instrument's controlling section usually consists of two metal antennas that function not as radio antennas but rather as position sensors. Each antenna forms one half of a capacitor with each of the thereminist's hands as the other half of the capacitor. These antennas capacitively sense the relative position of the hands and control oscillators for frequency with one hand, and amplitude 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.
History
The theremin was the product of Soviet government-sponsored research into proximity sensors. The instrument was invented in October 1920 by the Russian physicist Lev Sergeyevich Termen, known in the West as Leon Theremin. 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 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 bass-baritone Paul Robeson. Joseph Whiteley performed under the stage name Musaire and his 1930 RCA Theremin can be seen, played and heard at the Musical Museum, Brentford, England.
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, 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.
Both theremin instruments and kits are available. The Open Theremin, an open hardware and open software project, was developed by Swiss microengineer Urz Gaudenz, using the original heterodyne oscillator architecture for a good 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.
The theremin's singular operation method has been praised for providing an accessible route to music-making for people with disabilities.
Operating principles
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 their hands in the proximity of two metal antennas. While commonly called antennas, they are not used as radio antennae for receiving or broadcasting radio waves, but rather act as plates of capacitors. The distance from one antenna determines frequency, and the distance from the other controls amplitude. 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.
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 has significant body capacitance, and thus can be treated as the grounded plate of a variable capacitor in an L-C 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 linearisation 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 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 two or three 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 radio frequency 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 may use two pairs of heterodyne oscillators, for both pitch and volume.
Performance technique
Important in theremin articulation is the use of the volume control antenna. Unlike touched instruments, where simply halting play or damping a resonator in the traditional sense silences the instrument, the thereminist must "play the rests, as well as the notes", as Clara Rockmore observed.If the pitch hand is moved between notes, without first lowering the volume hand, the result is a "swooping" sound akin to a swanee whistle or a glissando played on the violin. Small flutters of the pitch hand can be used to produce a vibrato effect. To produce distinct notes requires a pecking action with the volume hand to mute the volume while the pitch hand moves between positions.
In 2004, thereminist Carolina Eyck invented a new and precise way to play the theremin, called the "8 finger position technique". For every octave there is a fixed arm position, and for notes within the octave fixed positions of the fingers, allowing very fast transitions between adjacent notes. With this technique the player is able to tune the theremin to their hand and rely on their finger positions, rather than correcting notes after they are audible.
Although volume technique is less developed than pitch technique, some thereminists have worked to extend it, especially Pamelia Kurstin with her "walking bass" technique and Rupert Chappelle.
The critic Harold C. Schonberg described the sound of the theremin as " cello lost in a dense fog, crying because it does not know how to get home".