OneTaskBy Tim King · Updated
Online Theremin
Play Pitch and Volume with Your Mouse or Finger, Free
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How the Online Theremin works
This online theremin plays pitch and volume from one pad. Press on the pad and move. Left to right sweeps the pitch smoothly with no keys or steps, up to the top of the pad is loud and down at the bottom is silent, and lifting off stops the note. Faint lines mark every semitone and brighter ones every C so you can find your way, the readout shows the nearest note and how many cents sharp or flat you are, and vibrato adds the wobble that gives a theremin its voice. On a phone or tablet it is played with a finger, which is closer to the real thing than a mouse.
Online theremin: how a theremin works
The theremin, invented by Leon Theremin in 1920, is played without being touched. Two antennas set up electric fields; the player's right hand near the vertical antenna raises the pitch and the left hand near the horizontal loop lowers the volume. Because there are no frets, keys or stops, every note has to be found by ear, and a player sings the pitch in their head and steers the hand to it. That is what makes it the hardest simple instrument there is, and why the sound slides and wavers the way it does. This page keeps the two-axis idea and swaps the antennas for a pad.
Playing it
The trick, as with the real instrument, is to lead with the volume hand. Come onto the pad near the bottom where it is quiet, slide sideways to the note you want, then move up to bring the volume in. Moving between notes with the volume up gives the classic swoop; dipping low between them gives something closer to separate notes. Glide sets how quickly the pitch follows the pointer: zero tracks instantly, a hundred milliseconds or more smooths a shaky hand into a slow portamento.
Range and pitch lines
Octaves across the pad sets how much pitch is packed into the width. Two octaves is a good balance between range and control; one octave makes every semitone wide enough to hit reliably, four turns the pad into a siren. Lowest note sets where the left edge sits, from C2 in the bass up to A2. Pitch is mapped logarithmically so every semitone is the same width regardless of where it falls, which is how the ear hears it too.
Voice and vibrato
A real theremin produces something between a sine and a triangle, warm with a few harmonics, so Sine is the closest and Triangle a little brighter. Sawtooth is not theremin-like but makes an expressive lead. Vibrato modulates the pitch with a low frequency oscillator; five hertz at around twenty cents is what a thereminist's hand naturally does, and it hides small tuning errors as well as adding life to a held note. Set the depth to zero for a bare tone when practising intonation.
FAQ
Why does the note keep sliding when I want a clean jump?
Because a theremin has no steps; the pitch is wherever the hand is. To jump, drop to the bottom of the pad so the volume goes to nothing, move sideways, and come back up. Setting Glide to zero also removes the smoothing between pointer positions.
Can I play it with a touchscreen?
Yes, and it works better than a mouse because a finger gives you the same free two-axis motion as a hand near an antenna. The pad captures the touch so the page does not scroll while you play.
How do I know which note I am playing?
The readout under the pad names the nearest note and shows the offset in cents, and the brighter vertical lines on the pad mark every C. The note frequency table on this site lists what every line corresponds to if you want to mark a scale.
Does it use my microphone or camera?
No. The real instrument senses your hands with electric fields; this one only reads the pointer position, and nothing on the page uses the microphone, the camera or the network. Sound is generated by the browser's audio engine on your machine.
Why does it sound different from the recordings I know?
Classic theremin recordings run the instrument through a valve amplifier and a lot of room, and a skilled player shapes every note with the volume hand. Add vibrato around five hertz, use the sine voice, and practise the swell-in-then-slide motion, and the character comes through; the rest is hours of practice, as it is on the real thing.
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