therochord

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1 I

2 ii

3 iii

4 IV

5 V

6 vi

7 vii°

Chord modifiers (Hold + Chord)

Q Major

W Minor

E 7

R ♯

A Maj 7

S Min 7

D Dim 7

F ♭

Z Maj 6

X Min 6

C ø

V Aug 7

How to play therochord

therochord turns your number keys and mouse into a unique chordal accompaniment / theremin-style lead instrument. By Vic Wong, February 2026. The code is here: github

Mouse theremin: Click anywhere on the screen to activate the theremin. Drag up and down to change pitch. If you are on a mobile device, you can press and hold the yellow button and move your phone up and down for the same effect. The root (green) and diatonic (white) notes are highlighted on the right vertical bar.
Play Chords: Press 1-7 to play diatonic triad chords in the selected key. Hold to sustain the chord.
Modify: Hold a modifier key (like e for Dominant 7th) while playing to change the chord quality.
Transpose: Use the root ♯ and ♭ buttons to transpose the current chord.
Voice Leading: Tries to move notes as little as possible between chords for a smooth sound. This can be toggled on and off.
Change key: Use the dropdown to change key signatures, or hold Enter and press + or - to shift the key up or down a semitone.

Note: the numerical keypad doesn't have minor 6 and minor 7 chord modifier buttons. You can alternatively access these chords by holding the - key along with the / key (minor 7) or 8 key (minor 6). If your numerical keypad has a delete/backspace key, this can also be used as a minor 7.