The theremin is the only mainstream instrument you play by keeping your hands off it. A performer stands in front of a box with two metal rods and shapes melodies in thin air, and a change in electrical capacitance of roughly 0.01 picofarads between hand and rod can be enough to slide the pitch a full octave on a well-tuned model.
That hair-trigger sensitivity is why theremin performances look like sorcery on a phone screen, and why the instrument keeps turning up in short clips more than a century after its invention.
Two antennas, two jobs
A standard theremin has one upright rod and one horizontal loop. They are called antennas, but they never send or receive radio broadcasts. Each one acts as half of a capacitor, and the player’s hand, which is electrically grounded through the body, acts as the other half.
Usually the right hand works the vertical rod, which sets the pitch: the closer the hand, the higher the note. The left hand hovers over the loop, which sets the volume: bringing the hand nearer makes the sound quieter, and pulling it away makes it louder. Some players swap the arrangement, and cheap models replace the loop with an ordinary knob.
How a hand becomes a note
The trick is a technique called heterodyning. Inside the case sit two radio-frequency oscillators running below 500 kHz, far above anything a human ear can hear. One stays fixed. The other is tuned almost identically, but the player’s hand, by adding capacitance near the pitch rod, nudges its frequency.
A mixer then subtracts one frequency from the other. Two signals in the hundreds of kilohertz that differ by, say, 440 hertz produce a 440-hertz difference tone, the A above middle C. That difference is shaped, amplified and sent to a speaker. Move the hand a few centimeters and the gap between the oscillators changes, so the note glides.
The volume side uses a similar circuit. As the second hand approaches the loop, extra capacitance detunes a separate oscillator and reduces the current that drives the output, which quiets the sound.
Why it is so hard to play
With nothing to press, there are no frets, keys or fixed positions. Players must find each pitch by ear and muscle memory. The volume hand does the work a violinist’s bow or a pianist’s fingers would do: to separate two notes, the player briefly drops the volume while the pitch hand jumps, otherwise every change turns into a siren-like swoop. Clara Rockmore, the great concert thereminist of the 1930s, put it as playing “the rests, as well as the notes”.
In 2004 the German thereminist Carolina Eyck devised an “8 finger position technique,” which assigns a fixed arm position to each octave and fixed finger shapes to notes within it, letting players hit pitches before they sound rather than correcting them afterward.
A short timeline
- October 1920: Russian physicist Lev Termen, known abroad as Leon Theremin, builds the instrument while researching proximity sensors.
- 1928: He patents it in the United States and later licenses production to RCA.
- 1950s: High-school student Robert Moog starts building theremins, the experience he later credited with leading to the Moog synthesizer.
- 2019: 289 players in Kobe, Japan, set a Guinness record for the largest theremin ensemble, joined by three generations of the inventor’s family.
Hollywood made the sound shorthand for the uncanny, using it in scores such as Spellbound and The Day the Earth Stood Still. The critic Harold C. Schonberg compared its voice to “a cello lost in a dense fog, crying because it does not know how to get home”.
If you liked seeing physics turned into music, our story on a jazz solo played into a Rubens tube of dancing flames shows sound waves made visible, and our piece on the ancient Greek aulos and its leather face strap covers an instrument at the other end of musical history.
Modern kits keep the 1920 design alive. The Open Theremin project pairs the original two-oscillator layout with an Arduino board, and with a few extra parts it can send MIDI to trigger any synthesizer sound.
Further reading
Image: Philippe Smeyers, CC BY-SA 4.0 via Wikimedia Commons
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