24-TET Keys: Microtonal MIDI

Quarter tones on the piano board you already know. Morph 12-TET into 24-TET, play the notes between the notes by touch, and send them to GarageBand, Logic or AUM as MIDI.

Quarter tones on a keyboard you already know. 24-TET Keys is a microtonal keyboard for iPhone and iPad: play the notes between the notes with your fingers, hear them as you press them, and send them on as MIDI if you have somewhere to send them.

CAN YOU PLAY QUARTER TONES ON A PIANO? Not on an ordinary one, which is why quarter-tone pianos are rare instruments in a handful of cities. Here the piano board is the starting point. Naturals sit in a row, sharps ride above them, and the quarter tones grow into the gaps with an animated morph, so you can watch 24-TET come out of the notes you already play. Charles Ives wrote his Three Quarter-Tone Pieces for two pianos tuned a quarter tone apart.

WHAT DOES A QUARTER TONE SOUND LIKE? Press one. It makes sound out of the box, so you hear the interval instead of reading about it: polyphonic, played by touch, with glissando slides straight across the quarter tones. A quarter tone is half a semitone, 50 cents, the gap between two piano keys cut in two.

MICROTONAL CHORDS, NOT JUST SCALES Every finger is its own voice, so a neutral third holds its pitch inside a chord instead of dragging the other notes with it. That is the part quarter tones usually break.

LAYOUTS THAT MORPH INTO EACH OTHER This is an experimental collection of unusual keyboard layouts, and not a menu of separate boards: each is a point in one space, and any of them morphs into any other while you watch. The piano-derived board is one point. So is a domino board, where a key carries its natural below and its quarter tone above. So is a snake through the honeycomb. So is an isomorphic layout, where a chord shape is the same shape in every key, the property that makes hex boards worth learning. You can morph out of the piano you know straight into the honeycomb, the bridge between the two.

MICROTONAL MIDI KEYBOARD: SEND IT TO A DAW If you already make music and want quarter tones in it, this is the compact microtonal MIDI keyboard part. It sends over a virtual CoreMIDI source to GarageBand, Logic, AUM and other hosts, over USB, network MIDI or MIDI hardware. In poly mode each held note takes its own channel, so a quarter-tone chord arrives in tune; mono mode suits a single-channel instrument. Quarter tones travel as a pitch bend on the in-between notes.

WHAT IS 24-TET? 24-TET, also written 24 tone equal temperament and closely related to 24 EDO, cuts the octave into 24 equal steps instead of 12. Each step is a quarter tone. It is the tuning behind much modern microtonal and xenharmonic writing, and the usual way Western notation approximates Middle Eastern maqam. It is an equal temperament, not a Just Intonation system.

FAQ How do quarter tones work? They divide the semitone in half. 12-TET gives 12 equal steps per octave; 24-TET gives 24, so a new note lands exactly between every pair you already know. Which instruments can play quarter tones? Voices, fretless strings and many winds can bend to them; fixed-pitch keyboards usually cannot, which is what this app changes. Why don't we use quarter tones? Mostly because the instruments cannot play them. An ordinary piano has 12 keys per octave and no room for more. That is the limit this app removes. How do I make microtonal music with it? Play it as it is, or route the MIDI into your DAW and record the quarter tones onto a track like any other part. Can MIDI be microtonal? Yes. Each quarter tone travels as a pitch bend on the in-between notes, one voice per channel, so a chord stays in tune. Does it import Scala or .scl files? No. It plays 12-TET and 24-TET. Is it a tuner? No. It is a keyboard you play.

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Want a standalone instrument to just play? Try our companion app Fingerophone.