Harp
Introduction
Harps are instruments that have multiple strings perpendicular to the sound board, plucked by the player's hands. Each string corresponds to one pitch, which in the case of lever and pedal harps, may be modified by the lever or pedal mechanism to get more than one pitch. In the case of the pedal harp, the strings are tuned to a diatonic scale, and depressing a pedal (of which one is available for each note of the diatonic scale), depressing a pedal rotates a set of discs with pins set to stop the corresponding strings (in all octaves) so as to raise their pitch by a chromatic semitone (including allowance for the resulting slight increase in string tension). The double-acting pedal harp extends this concept to have two sets of string-stopping discs, actuated by successive further depressions of the corresponding pedal, which can be locked at either of its depressed positions; the strings are tuned to all flats, and the first depressed position of a pedal raises the pitch of the strings to achieve the corresponding natural notes, while the second depressed position of the pedal raises the pitch further to achieve the corresponding sharp notes. The modern double-acting harp also has two lowest C and D strings and one highest G string to which this mechanism does not apply, so these strings are tuned to whichever pitches are required for the music being played.
The problem for microtonalists
Unfortunately, the above design in its standard implementation is wedded to 12edo — the value of the chromatic semitone is fixed, and a standard pedal harp has no provision for adjusting the position of the string stops, nor for partial action of the string stops attempting to move a pedal to an intermediate position does not produce an in-between note, but instead produces a buzz or a fearsome rattle (depending upon how hard the string was plucked) as the string hits the pins on the incompletely turned disc. The only microtonal tuning systems that can make efficient use of pedal harps to get in-between notes are multiples of 12edo, with multiple harps tuned to different rings of 12edo, as done by Ivan Wyschnegradsky with pianos. Although no recording is known of actual harp use in this way, Norokusi has written a composition in 24edo, rendered by soft synthesizers, that uses this technique (see below); in principle, it could be transcribed and then played on a full set of acoustic instruments, including two harps with the orchestra. Thus, microtonality on most harps (unless using multiple harps) is limited to whatever can be achieved by retuning the available 7 strings per octave. See the music section below for examples of obtaining microtones by retuning individual strings and retuning two or more harps offset by one step within a multiple of 12edo.
Demonstration of harp string buzz
A solution that does not yet exist
An instrument called a "fluid harp" exists that has sliders to enable continuously-variable pitch variation on each string, as demonstrated in Fluid Harp – Adjustable Microtonal Harp (2017), but it is actually a zither and produces a very different tonal quality from a harp; as such, it belongs to a page about zithers, and is not further covered here. In principle, such a mechanism — or better yet, a pedal-actuated slider mechanism — could be applied to an actual harp, but so far, none have been built.
One solution: (some) lever harps
Lever harps have one lever for each string to tighten and/or stop the string to raise the pitch by a chromatic semitone (one disadvantage being that the levers do not have enough range to go all the way from a flat to a sharp). On a subset of lever harps, it is possible to achieve in-between notes as well as portamento and vibrato by moving levers to intermediate positions; on a subset of these harps (including the Harp-E), the levers have enough friction to stay in an intermediate position after being moved there. Since the levers operate independently, changing all of the notes in a pitch class requires changing the positions of all of the corresponding levers, and this will require too much time to achieve in a rapidly modulating passage.
Demonstration
- Levers AND bends! (2024)
Another solution: manual string stopping
Another possible solution is to wear a metal cylinder on one finger and use it to stop pairs of adjacent strings. This enables any amount of pitch bend (potentially while plucking these and nearby strings with other fingers on the same hand), and can be used on any harp, although it only applies to one pair of strings at a time for each metal tube (conceivably, one could wear a metal tube on one finger on each hand to do this with two pairs of strings). See the music section below for examples of manual string stopping.
Yet another solution: more strings
The cross-strung harp or chromatic double harp foregoes changing the pitch of strings to get accidentals and instead has more strings — usually one row of 7 strings per octave tuned to a diatonic scale of the natural notes and one row of 5 strings per octave tuned to a pentatonic scale of the sharp/flat notes. (A few have been made that instead have twin whole-tone scales.) Since the strings are only tuned using the normal tuning mechanism (unless one stops the strings with a metal tube as above), it is in principle possible to tune the strings to sound in a 12 notes per octave subset of tuning systems other than 12edo, including complete tuning systems having less than 12 notes per octave.
The triple harp (including the Welsh version) has even more strings, with 2 outer rows of 7 strings each normally tuned to the natural notes and a middle row normally tuned to the flat/sharp notes as indicated above. Again, since the strings are only tuned using the normal tuning mechanism (unless one stops the strings with a metal tube as above), it is in principle possible to tune the strings to sound in a 19 notes per octave subset of tuning systems other than 12edo, as well as complete tuning systems of up to 19 notes per octave, including 19edo.
Unfortunately, no music or other demonstration appears to be available at this time for these types of harps.
Music
Despite the general unfriendliness of the predominant harp design towards microtonality, some microtonal music has been composed, played (or rendered as a proof of concept), and recorded. For some of this music, the method of obtaining microtones was not described; this music is in "Unspecified method of obtaining microtones" at the end; if the method is discovered, it should be moved to one of the other sections (or a new section created, as appropriate).
Manual string stopping
- KHEÍRŌN opus 53, Nocturne pour harpe – Caroline Lizotte (Juliette Duguay, harpiste) (2026) (uses the metal tube on finger technique)
Retuned individual strings
- Ma manière de chat (1979) (from video comments: some strings are tuned down by a quarter-tone)
- Microtonal Semi-improvisation on Harpsicle/Folk Harp! (2019) (the harp is tuned to 1/1, 9/8, 5/4, 4/3, 3/2, 14/9, 7/4)
Retuned multiple harps
- Norokusi (both examples using dual harps tuned apart by 1\24, rendered by soft synthesizer, but in principle playable on acoustic instruments)
Unspecified method of obtaining microtones
- Étrennes (1992), from Catherine Michel En Récital (by analogy with Ma manière de chat, may be using retuning of individual strings, but not confirmed)