An isomorphic keyboard is a musical input device consisting of a two-dimensional grid of note-controlling elements (such as buttons or keys) on which any given sequence and/or combination of musical intervals has the “same shape” on the keyboard wherever it occurs – within a key, across keys, across octaves, and across tunings.
Isomorphic keyboards were developed by Bosanquet (1875), Janko (1882), Wicki (1896), Fokker (1951), Erv Wilson (1975-present) and Wesley (2001). The keyboards of Bosanquet and Erv Wilson are also known as generalized keyboards.
Isomorphic keyboards expose, through their geometry, two invariant properties of music theory:
- transpositional invariance, in which any given sequence and/or combination of musical intervals has the same shape when transposed to another key, and
- tuning invariance, in which any given sequence and/or combination of musical intervals has the same shape when played in another tuning of the same musical temperament.
Basis vectors 
A two-dimensional lattice is generated by two basis vectors, and so is a rank-2 regular temperament of Just Intonation. A keyboard lattice generated by two given musical intervals will be isomorphic in any rank-2 temperament that is also generated by those same two intervals. For example, an isomorphic keyboard generated by the octave and tempered perfect fifth will be isomorphic with both the syntonic and schismatic temperaments, which are both generated by those same two intervals.
Two primary benefits are claimed by the inventors and enthusiasts of isomorphic keyboards:
- Ease of teaching, learning, and playing
- isomorphic keyboards' provision of more than the usual 12 note-controlling elements per octave facilitate the performance of music that requires more than 12 notes per octave.
A third potential benefit of isomorphic keyboards, dynamic tonality, has recently been demonstrated, but its utility is not yet been proven. Using a continuous controller, a performer can vary the tuning of all notes in real time, while retaining invariant fingering on an isomorphic keyboard. Dynamic Tonality has the potential to enable new real-time tonal effects such as polyphonic tuning bends, new chord progressions, and temperament modulations, but the musical utility of these new effects has not yet been demonstrated.
Isomorphic keyboards can be compared and contrasted using metrics such as the thickness of an octave's swathe of buttons on the keyboard and the number of repetitions of a given note on the keyboard. Different isomorphic keyboards are suited for different uses. Within the syntonic temperament's broad tuning continuum, for example, the Fokker keyboard is well-suited to tunings of the syntonic temperament in which the tempered perfect fifth stays in a narrow range around 700 cents, whereas the Wicki keyboard is useful over the syntonic temperament's entire tuning range.
- Qwertonic – free UK site containing Java, Flash, and PC applications to enable users to play their alpha-numeric keyboard to sound 12 equal tempered pitches using Wicki/Janko layout.
- Relayer – a free application that enables musicians who play the AXiS-49, the QWERTY computer keyboard, or the Thummer, to play in a wide variety of isomorphic note layouts and tunings (even with a standard multitimbral synth).
- Musix – iPhone and iPad app. Musix is a fully customizable multiple-layout isomorphic musical keyboard.
- IsoKeys – Android app. IsoKeys is a free customizable isomorphic musical keyboard that supports several popular layouts.
- Hexiano – Android app. Hexiano is a free and open-source customizable isomorphic musical keyboard that supports several popular layouts.
|Wikimedia Commons has media related to: Isomorphic keyboard layouts|
- Balanced Keyboard A modified symmetrical layout of the standard keyboard. The website shows how to build your own.
- Demo, Demonstration of the advantages of the isometric keyboard (Janko version) by Paul Vandervoort, considered to be the world's foremost player of the device. Program: "Kitten on the Keys" by Zez Confrey; explanation of the Janko note arrangement and advantages over a standard keyboard; demonstration of musical passages which are difficult or impossible to play on a standard keyboard; "C#-Major Prelude" from the Well-Tempered Clavier by J.S. Bach; Boogie-woogie rendition of "Bye Bye Blackbird".
- Isomorphic Instruments at The Music Notation Project Wiki
- クロマトーン Inspiration 9:59 #1/11 played on the Chromatone (kuromatōn / クロマトーン), a Jankó-like isomorphic keyboard. The first in a series of 10 such "Chromatone Inspiration" videos.
See also 
- Keislar, D., History and Principles of Microtonal Keyboard Design, Report No. STAN-M-45, Center for Computer Research in Music and Acoustics, Stanford University, April 1988.
- Milne, A., Sethares, W.A. and Plamondon, J., Invariant Fingerings Across a Tuning Continuum, Computer Music Journal, Winter 2007, Vol. 31, No. 4, Pages 15-32.
- ThumMusic System.
- Wholetone Revolution.
- C-Thru Music.
- The Shape of Music.
- Milne, A., Sethares, W.A. and Plamondon, J., Tuning Continua and Keyboard Layouts, Journal of Mathematics and Music, Spring 2008.