This layout is a natural mapping to harmony. Click this to play Debussy’s Passepied.
press a purple key to change the harmony. These green text links will play sound. (Make sure your sound is on. If you’re on mobile, you will have to tap once before it’ll let you play, and make sure the Silent Mode switch is off.)
The biggest difference from a piano is that you can play all the notes together (volume warning). This is a unique set of notes. As a consequence, random keys harmonize with each other, and even rolling your elbow over the keyboard or sweeping your mouse will sound pleasant. If you hold 3 notes and don’t hear the 3rd note, then your keyboard can only handle 2 keys at a time, which is unfortunately common. In that case, use the mouse and keyboard simultaneously. On mobile, horizontal view will make the buttons bigger.
The pitch of a green key is its number. The purple numbers multiply all the pitches, and purple numbers on the left (7/6) are more exotic than ones on the right (1/2).
Computer keyboards don’t have enough thumb keys for this instrument. With those thumb keys, this instrument would be able to play everything a piano can. This is from research on harmony, described in a later section. The principle is that harmonic pitches in a region can be multiples of at most 2 fundamentals, and are more consonant if there’s only 1 fundamental. The green keys have all the relevant multiples of a fundamental, and thumb keys would enable two fundamentals. In practice, 1 fundamental is enough to play the consonant chords and most of the moderately dissonant chords. The extra fundamental is for things like embedded tritones and minor-major chords.
The fundamental captures the harmonic context, very similar to what tonality is. There’s a logical pattern to the green keys that accords with consonance, described at this link. This combination of fundamental and pattern creates a wonderful map: the distance between keys on the keyboard represents how dissonant they are with each other. Purple keys increase distance.
In improv and composition, this distance frees you to think about harmony rather than calculate intervals, since you can tell without calculation or memorization what the consonance will be and which notes will work. This is even more helpful for beginners, who may not know the correct intervals; the keyboard reveals them.
With these numbers, you can read consonance without memorizing chords, even for complex chords like stacked and secondary chords. Broadly, a chord is consonant if it has small numbers in its reduced fractions. For example, 8 6 is consonant because 8/6 = 4/3 has small numbers. 4 7 is dissonant because 4/7 has the large number 7. A further condition for consonance is that linear combinations of numbers should be either exactly at 0 or far from 0. So ratios close to 1 are dissonant (like 15 16). Arithmetic sequences are consonant when exact (12 16 20, 12-16=16-20) and dissonant when inexact (12 15 20). Sums are consonant when exact (6 10 16, 6+10=16) and dissonant when inexact (6 10 15).
The specific harmony insight that this instrument enables is these linear combinations. For example, if you want to compare a minor chord and major chord, they have the same semitones, hence the same pairwise ratios: 4:5:6. However, you know that in the major chord, these are in an arithmetic progression and hence are consonant, while the minor c
