Twelve TheoryMath + Music Playground

Explore interactive music theory and music by numbers through Free Play, Math Mode, Chord Game, the Note Stage, Circle Counting, the Triad Chart, Church Modes, Harmonic Cone, the Harmonics Quiz, Frequency Chart, Harmonic Wave, Waveforms, Harmonic Polygons, Tuning String, Sheet Music, Musical Circles, and Ear Training.

Free play
Keyboard view
Number-pad pianoHold multiple keypad numbers to play them together.

Computer keyboard1–90 or * = 10− = 11= = 12O = octave downP = octave upEnter = next

Press and hold a number to hear it.

Play scale from
Instrument
Tuning

Just tuning uses pure major-scale ratios around one selected key. Equal temperament unlocks every key.

Two-octave rangeShown octave · O/P
Grid

Hold a pad to sustain it and release to stop. Hold multiple pads to hear the tones together.

How to build a major scale

Odd tonic: 3 consecutive odds → 4 consecutive evens → tonic

Even tonic: 3 consecutive evens → 4 consecutive odds → tonic

From 1: 1–3–5–6–8–10–12–1From 2: 2–4–6–7–9–11–1–2
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