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Pianos, harpsichords and organs are suited for microtonal music insofar as the strings/pipes can, within limits, be tuned to anything desired.

In the case of harpsichords and organs, the probablity that tuning issues arise is even slightly higher than average since there is often "old" music (baroque and older, from the pre-well-tempered age) being played on them.

For electronic instruments (syntheszers), there is, in theory, absolute freedom for the pitches anyway - not in practice, though. But nowadays, many synthesizers have a built-in retuning functionality. A broad overview over the microtonal capacities of synthesizers can be found on www.microtonal-synthesis.com.

A side-remark: Synthesizers, even without retuning functionality, often have a special functionality that is principally also suited for microtonality: the modulation wheel. An impressive example of how to make microtonal music with the modulation wheel can be found here. This is, however, not a particularly easy way to do it...

Strategies for more than 12 tones per octave

A potential source for troubles is the traditional keyboard design, which is optimized for diatonic scales and 12 tones per octave.

For microtonal music with not more than 12 tones per octave, this is not such a problem - fingerings for non-standard scales can be learned. But it becomes a problem if you need more than 12 tones per octave, or even want a non-octave tuning, such as Wendy Carlos or Bohlen-Pierce.

There exist several solutions for this problem:

1) 12 Note Octave Scales

(Terminology from www.microtonal-synthesis.com)
Use several keyboards whose keys are slightly detuned against each other.

Advantages are that the keyboard layout keeps the familiar property that 12 key steps span one octave, and the pitches typically need only minor retuning. This is not unimportant for acoustical instruments, where we usually have physical limits to the amount a pitch can be retuned. For this reason, this approach is widely used, especially in the field of contemporary classical music.

The disadvantage is, of course, that you need several keyboards. In the case of acoustic pianos, this means in practice that the maximal number of pitches per octave you can obtain is limited - to the number of pianos you can put on the stage together... "Arc-en-ciel" by Ivan Wyschnegradsky, for example, a piece in 72edo, is written for six (!) pianos, and "Limited approximations" by Georg Friedrich Haas, in 72edo as well, needs the same number of pianos and moreover a whole orchestra...

Electronic keyboards sometimes have the possibility to play in "split" mode, i.e. the upper and the lower half of the keyboard can send to different midi channels. Some keyboards offer up to 4 split areas. In this case, you need only one keyboard - but you still have the disadvantage of having to jump between the areas.

12 note octave scales piano tuning instructions for 17edo
12 note octave scales piano tuning instructions for 19edo
12 note octave scales piano tuning instructions for 22edo
12 note octave scales piano tuning instructions for 24edo
12 note octave scales piano tuning instructions for 41edo

2) Full Keyboard Scales

(Terminology from www.microtonal-synthesis.com)
Tune each key of the keyboard to a different pitch. The pitches of the keys keep the property of being arranged in ascending order - but the octave pattern will be different, and there are larger amounts of retuning required.

Some synthesizers support this, but not all (see, again, www.microtonal-synthesis.com).
Synthesizers supporting only 12 note octave scales can be brought to support full keyboard scales with the help of the Midi Integrator software, or the alt-tuner software.

A possible "full keyboard scales" piano tuning for 22edo, mapping two keyboard octaves to one acoustic octave, is decribed in Paul Erlich's paper on 22edo, on page 11.

In the case of acoustical instruments such as pianos, tuning full keyboard scales may even require major changes in construction. It has been done, however, e.g. on the 16th tone (96edo) piano.

3) Dynamic Tunings

Some instruments allows their tuning to be changed "on the fly", allowing access to more than 12 notes, although not all at once. The main advantage is that the keyboard layout keeps the familiar property that 12 key steps span one octave. The main disadvantages is that certain melodies will be unplayable, such as a rapid passage using more than 12 notes.

For example, the Turkish kanun is a diatonic instrument like a hammer dulcimer, but plucked, not struck. Each set of strings has a set of mandals, a tiny lever which when flipped changes the length of the string and microtonally changes the pitch. It's analogous to the sharpening levers on the celtic harp, but there are mote than one lever per string, and they sharpen considerably less than a semitone.

The easiest way to experiment with dynamic tunings is with midi keyboards and software. Scala and Lil' Miss Scale Oven have limited dynamic tuning ability. Alt-tuner allows retuning of individual notes (choosing among various ratios or among various EDO degrees), modulating to different keys (either by a specific interval, or to a specific note, or to the current bass note), and switching to completely different tunings. All this can be done via keyswitches, foot pedals, the mod wheel, or any control that generates a midi signal. These midi signals can come from any midi device, such as a 2nd keyboard, or even the computer's QWERTY keyboard. Technique-wise, using keyswitches would be similar to using mandals or sharpening levers, and using footpedals would be similar to using the classical harp's pedals.

4) Get an alternative keyboard!

This is actually quite an old idea, since in historical tunings of the pre-well-tempered area, there was a demand for differing between flats and sharps.

www.denzilwraight.com has some beautiful examples of historical harpsichords with up to 24 keys per octave.
A list of existing church organs all over the world with split semitone keys can be found on Ibo Ortgies' homepage.

In modern times, the idea of generalized keyboards has come up again. Generalized keyboards can host the same fingering for multiple tunings. See, for example:

Wikipedia article isomorphic keyboards
Wikipedia article on generalized keyboards
Wikipedia article on Bosanquet
Wikipedia article on harmonic table note layouts
Wikipedia article on the Wicki-Hayden note layout
Wikipedia article on Janko

For electronic music, there is meanwhile a number of generalized keyboards that are available or are soon to be available, see followng list.

List of available generalized keyboards

No. of keys
Terpstra keyboard
Cortex design
2-dimensional, hexagonal
2-dimensional, hexagonal
Tonal Plexus U-PLEX, Tonal Plexus TPX2, Tonal Plexus TPX2s
Hπ Instruments
2-dimensional, rectangular
Tonal Plexus TPX4
Hπ Instruments
2-dimensional, rectangular
Tonal Plexus TPX6, Tonal Plexus TPX6s
Hπ Instruments
2-dimensional, rectangular
Hπ Instruments
Various (hexagonal, rectangular, 1-dimensional et al.) XXX
C-Thru Music
2-dimensional, hexagonal
C-Thru Music
2-dimensional, hexagonal
Opal Chameleon, Opal Gekko
2-dimensional, hexagonal
Monome 64
2-dimensional, rectangular
Monome 128
2-dimensional, rectangular
Monome 256
2-dimensional, rectangular
Lippens Keyboard


Daskin 5
Daskin Manufacturing
Janko (2-dimensional)
Daskin 6
Daskin Manufacturing
Vertical keyboard (Elaine Walker)
Elaine Walker
1-dimensional, 2 tiers of keys (black/white), with customizable black/white pattern
61, 76 or 88
Metatonal Keyboard
Metatonal Music (Ron Sword)
1-dimensional, 2 tiers of keys (black/white), with customizable black/white pattern

ZB2 Z-Board
Starr Labs
2-dimensional, rectangular
Microzone U-648
Starr Labs
2-dimensional, hexagonal
Microzone U-990
Starr Labs
2-dimensional, hexagonal
Dualo Du-Touch
2-dimensional, hexagonal

A special class of microtonal midi controllers are "keyless" ones:
Continuum Fingerboard
Haken Audio
R2M Ribbon Controller
Roger Linn Design
SoundPlane A
Madrona Labs

Pad controllers:

[[http://global.novationmusic.com/midi-controll%E2%80%A6/launchpad-pro|Novation Launchpad Pro]]
Behringer CMD LC-1


Alternative Keyboards group (on Google groups)
John Starrett on Completely Generalized Keyboards - https://www.facebook.com/notes/john-starrett/completely-generalized-keyboard/426265927629

DIY links

Monome Gridkit - Monome DIY kit slashes price of pre-built one.

TouchKeys Kickstarter Campaign - https://www.kickstarter.com/.../touchkeys-multi-touch...
TouchKeys Website - http://www.eecs.qmul.ac.uk/~andrewm/touchkeys.html
There's a mapping in the TouchKeys software which splits each key into multiple regions specifically for microtonal music.
Here's a video demo using it to play Turkish maqam music - https://www.youtube.com/watch?v=-QcYgslHq9k...
You don´t need even need keyboard - http://youtu.be/CHWVeQd0bYs?list=UUad1IRAVR2klHEtNoS4TsaA

Touch Screens in general:
Here's an article discussing available touch screen technologies per 2010 - http://www.eizoglobal.com/.../basic_understanding_of.../
Some more overview - http://www.elotouch.com/Products/detech2.asp
Wikipedia - http://en.m.wikipedia.org/wiki/Touchscreen#Technologies
Finally this one - http://www.cammaxlimited.co.uk/what-are-the-different.../
Multitouch Interaction Research - http://cs.nyu.edu/~jhan/ftirtouch/

Touch Screen Approaches:
You could make something like this yourself (costs 15.000 dollars) - http://youtu.be/UP9zt_JbrHI
Acoustic Touch Demo - http://youtu.be/ZoAslMiukAQ
Peau Productions sells affordable custom size infrared frames for diy solutions - http://youtu.be/C-R8PmaIy-w
IR frames are pretty cool - http://youtu.be/ZOYDERT-p_g

Gesture Based Controllers:
You can use Kinect to make a "virtual keyboard" that only exists in "kinect space" - http://youtu.be/ZqtrH5nQjFc
Airpiano - http://www.airpiano.de

Apple Magic Trackpad:
What about the Apple Magic Trackpad? - http://youtu.be/m9KdWuOTpMQ
String a number of Trackpads together with this - http://store.apple.com/.../H3443ZM/A/twelve-south-magicwand
Add a keyboard layout layer using something like this - http://www.amazon.com/Mobee-Technology.../dp/B005M1777G...
The software is already there for one Trackpad, so why not for more than one? - http://createdigitalmusic.com/.../track-master-makes.../

Mechanical Keyboard Switches:
DIY Isomorphic Keyboard Project 1 - http://youtu.be/KfjEYu79J-4
DIY Isomorphic Keyboard Project 2 - http://t.walyou.com/all/diy-isomorphic-keyboard#1
DIY Isomorphic Keyboard Project 3 - http://mods-n-hacks.wonderhowto.com/.../diy-illuminated.../
Mechanical Keyboard Switches Guide 1 - http://www.daskeyboard.com/blog/mechanical-keyboard-guide/
Mechanical Keyboard Switches Guide 2 - http://deskthority.net/wiki/Cherry_MX

Lemur Canvas Object lets you script custom widgets with full multitouch support - https://liine.net/en/products/lemur/

Livid DIY platform for MIDI control surfaces - http://lividinstruments.com/products/builder/
Madrona Labs DIY - http://madronalabs.com/DIY
Midi boutique makes parts for Hπ Instruments - http://www.midiboutique.com
DIY Keyboard Wiki - http://diykeyboard.wikidot.com

Other MIDI controllers:

Keyboard Concepts

New Keyboard (Johannes Kotschy)