How to use it
This is a virtual theremin. Press the mouse button on the large pad, or touch it, and drag. Moving right raises the pitch and moving up makes the sound louder. Release and the sound fades out. There are no keys or frets: every position gives a pitch, which makes the real instrument expressive and hard to play in tune.
The sound stays off until your first press on the pad (or first press of Space), because browsers only allow audio after a user action. If you hear nothing, check the Mute button, the volume slider and the volume of your device. The very bottom of the pad is silent. Start with a slow slide at a steady height, then try to land on a note you can hear in your head. To play a tune without hunting for the exact spot, turn on Snap to scale.
Controls
- Pad: drag with a mouse or finger. Vertical lines mark notes and carry their names.
- Keyboard: Tab to the pad. Left and right arrows change pitch by a semitone (Shift: an octave), up and down change volume. Space holds the note until you press it again. Esc stops everything.
- Range: the lowest note (C2 to C5) and the width of the pad in octaves (2 to 5). The top note is limited to C8.
- Snap to scale: off, chromatic, major, minor or major pentatonic, with a root note. Glide sets how long the pitch slides to each snapped note.
- Vibrato: rate in hertz and depth in cents.
- Tone: four built-in waveforms (sine, classic, triangle, soft saw) and an optional echo.
- Replay: records your last phrase (up to 30 seconds) and loops it (a tap shorter than half a second does not replace an earlier phrase), with the dot and trail moving by themselves. Press Stop replay, or touch the pad, to take over.
- Volume and Mute: master volume and an instant mute. The readout shows the note, its cents from the nearest equal-tempered note, its frequency and the level.
How it works
The real theremin is played without touching it. Inside are two radio-frequency oscillators, far above the range of hearing. One has a fixed frequency. The frequency of the other depends on a resonant circuit that includes the pitch antenna, a metal rod. Your hand and body act as the second plate of a capacitor, so the nearer your hand is to the antenna, the larger the capacitance becomes. A resonant circuit oscillates at:
More capacitance means a lower frequency. The two radio signals are mixed, and their difference, the beat frequency, is audible and gets amplified:
For example, 300,000 Hz and 299,560 Hz give an audible 440 Hz. A second circuit with a loop-shaped volume antenna controls an amplifier: bringing the hand towards the loop lowers the loudness. Pitch changes steeply near the pitch antenna, so players learn the instrument by ear.
This page does not simulate the electronics. It turns the position of the playing point straight into a frequency using musical logic. With x from 0 (left) to 1 (right), the note number is m = mlow + 12 · octaves · x, and the frequency is:
Here m = 69 is the A above middle C at 440 Hz and each step of 1 is a semitone. Because each octave doubles the frequency, equal distances on the pad are equal musical intervals. Cents measure the gap between frequencies: 1200 · log2(f2/f1). One oscillator makes the sound, a slow oscillator wobbles its pitch for vibrato, and a short delay line makes the echo.
The instrument was invented by the Russian physicist Lev Termen, known in the West as Leon Theremin, in the early 1920s, and a US patent followed in 1928. It is one of the earliest electronic instruments and the best known one played without contact. It has been used in film music and recordings.
Things to try
- Slide slowly across one octave at a constant height and listen to the even steps.
- Choose Major with root C and compare Glide at 0 and 200 ms.
- Pick Pentatonic with root A and improvise.
- Set the vibrato to 6 Hz and 30 cents, then raise the depth to 100 cents for a siren-like sound.
- Narrow the pad to two octaves and see how much easier it is to land on a note.
- Play a short phrase, press Replay and play along over it with the echo switched on.
Frequently asked questions
Is this a real theremin?
No. The sound is synthesised in your browser from the position of your pointer. There is no antenna or capacitance, but the playing idea is the same: continuous pitch and volume, no keys.
Why is there no sound?
Check that the button says Mute (not Unmute), that the volume slider is above zero and that you are not at the very bottom of the pad. Audio starts only after your first press on the pad or on Space.
Why is the pitch scale logarithmic?
We hear equal frequency ratios as equal intervals. An octave is always a doubling, so each octave gets the same width on the pad.
Why does the readout show cents?
Without snapping you are rarely exactly on a note. Cents show how far above or below the nearest note you are; the value is 0 when snapped.
Are my settings saved?
Yes, in your browser’s local storage on your device. Your recorded phrase is not stored or sent anywhere.