Show HN: Just intonation keyboard – play music without knowing music
This is a keyboard in just intonation. It can play the notes a piano can. The big difference from a piano is that all the notes become consonant. At least, when you want to play a dissonant chord, you are clearly opting in to it because it's clear which notes are dissonant to each other. You won't bump into a dissonant note by mistake.

You can play without knowing any music theory. Hit arbitrary notes with the rhythm you want, and the pitches will work. Not understanding the buttons is fine. Even rolling your elbow around your keyboard is fine.

If you are a musician and press the wrong key while playing a song, it will still fit. It will sound like you made an intelligent, conscious choice to play another note, even though you know in your heart it was an accident. Beginner jazz musicians rejoice.

It's not an AI making choices for you; it's just a very elegant interface. What makes this possible is several new discoveries in psychoacoustics about how harmony works. While a piano lays out notes in pitch space, this keyboard is able to lay out notes in consonance space. When you play random notes, they tend to be "close together" on the physical keyboard. Distance on the keyboard maps well to distance in consonance space, so those random notes are close together in consonance space and sound good together.

According to Miles Davis, a "wrong" note becomes correct in the right context. If you try to play a wrong note, the purple buttons you press will automatically land you in the right context, even if you don't know what that context is yourself. So you can stumble your way through an improv and the keyboard will offer the right notes without needing you to think about it.

Harmonic consonance of chords can be read directly off the numbers in the keyboard, which implies that these numbers are a good language to think about music with. It doesn't take years of training, just reading the rules. The key harmony insight that you can do on this keyboard, and not on a piano, is to add frequencies linearly (like 400 Hz + 300 Hz). The reason this matters is that linear combinations of frequencies are a major factor of harmony, in lattice tones. So to see how dissonant or consonant a chord is, you want to check how distant it is from a sum or arithmetic progression. On a piano, to do the same, you'd have to memorize fractional approximations of 2^(N/12), then add and subtract these fractions, which is very difficult. For example, how far is 6/5 + 4/3 from 5/2? Hard to say! But if denominators are cleared, it's easy to compare 36 40 45: they're off by 1 from an arithmetic progression. This also applies to overlapping notes, not just chords. Having all the keys accessible on a piano is very convenient, but this translation layer of 2^(N/12) approximation + fractional arithmetic makes it hard to see harmony beyond the pairwise ratios.

The subset of playable songs is different from a piano, which means that songs in your existing piano repertoire will snip off some notes. Hardware for thumb keys would fix this, so you could play your existing piano songs in full, plus other songs a piano can't play. I don't have such hardware so I haven't implemented this. The other way is to have two keyboards and a partner.

The remaining issue is that there is no sheet music in just intonation. Unfortunately, I have had no success in finding piano sheet music in a common, interpretable format. So while I do have a converter from 12 equal temperament to just intonation, there are no input files to use it with...