43 tone equal temperament
43edo divides the octave into 43 equal parts of 27.907 cents each. It is strongly associated with meantone temperament, particularly 1/5 comma meantone, being a good tuning system in the 5, 7, 11, and 13-limit. The version of 11-limit meantone is the one tempering out 99/98, 176/175 and 441/440 sometimes called Huygens. 43-equal has the first good 13-limit meantone available as an equal division of the octave. The baroque, french, ironically hearing and speech impaired acoustician Joseph Sauveur based his system on 43 equal tones to the octave, calling them "merides". Further information: http://tonalsoft.com/enc/m/meride.aspx
In the 13-limit, we get two versions of meantone equivalent in 43et, one, meridetone, tempering out 78/77, the other, grosstone, 144/143. Meridetone has generator mapping <0 1 4 10 18 27|, and grosstone <0 1 4 10 18 -16|; 43 supplies the optimal patent val for meridetone.
The 43 patent val <43 68 100 121 149 159| maps 5 to 100 steps, allowing the divison of 5 into 20 equal parts, leading to jerome temperament, an interesting higher-limit system for which 43 supplies the optimal patent val in the 7, 11, 13, 17, 19 and 23 limits. It also provides the optimal patent val for 11- and 13-limit amavil temperament, which is not a meantone temperament. Thuja temperament is also a possibility, in which five generators, (~11/8)^5 = ~5/1, with MOS of 15 and 28.
Although not consistent, it performs quite decently in very high limits. It has unambiguous mappings for all prime harmonics up to 64, with the sole exceptions of 23 and, perhaps, 41. The mappings for composite harmonics can then be derived from those for the primes, giving an almost-complete version of mode 32 of the harmonic series, although the aforementioned lack of consistency will give some unusual results. Indeed, the step size of 43edo is very close to the septimal comma (64:63), while two steps is close to 32:31, and four steps to 16:15.
|Degrees||Cents value||Approximate 13-limit Ratios||ups and downs notation|
|1||27.907||^1, d2||up unison, dim 2nd||D^, Ebb|
|2||55.814||vA1, ^d2||downaug unison, updim 2nd||D#v, Ebb^|
|4||111.628||17/16, 16/15, 15/14||m2||minor 2nd||Eb|
|5||139.535||12/11, 13/12, 14/13||^m2||upminor 2nd||Eb^|
|7||195.349||9/8, 10/9||M2||major 2nd||E|
|9||251.163||15/13||vA2, ^d3||downaug 2nd, updim 3rd||E#v, Fb^|
|10||279.07||7/6, 13/11||vm3||downminor 3rd||Fv|
|12||334.884||17/14, 39/32||^m3||upminor 3rd||F^|
|13||362.791||11/9, 16/13||vM3||downmajor 3rd||F#v|
|15||418.605||9/7, 14/11||^M3||upmajor 3rd||F#^|
|16||446.512||13/10||vA3, ^d4||downaug 3rd, updim 4th||Fxv, Gb^|
|20||558.139||11/8, 18/13||vA4||downaug 4th||G#v|
|21||586.046||7/5||A4, vd5||aug 4th, downdim 5th||G#, Abv|
|22||613.953||10/7||^A4, d5||upaug 4th, dim 5th||G#^, Ab|
|23||641.86||16/11, 13/9||^d5||updim 5th||Ab^|
|27||753.488||20/13||vA5, ^d6||downaug 5th, updim 6th||A#v, Bbb^|
|28||781.395||14/9, 11/7||vm6||downminor 6th||Bbv|
|30||837.209||18/11, 13/8||^m6||upminor 6th||Bb^|
|34||948.837||26/15||vA6, ^d7||downaug 6th, updim 7th||B#v, Cb^|
|36||1004.651||16/9, 9/5||m7||minor 7th||C|
|38||1060.465||11/6, 24/13, 13/7||vM7||downmajor 7th||C#v|
|39||1088.372||15/8, 28/15||M7||major 7th||C#|
|41||1144.186||vA7, ^d8||downaug 7th, updim 8ve||Cxv, Db^|
|42||1172.093||A7, v8||aug 7th, down 8ve||Cx, Dv|
The distance from C to C# is 3 keys or frets or EDOsteps. Thus one up equals one third of a sharp. Chords can be named using ups and downs as C upminor, D downmajor seven, etc. See Ups and Downs Notation - Chord names in other EDOs.
Selected just intervals by error
The following table shows how some prominent just intervals are represented in 43edo (ordered by absolute error).
|Interval, complement||Error (abs., in cents)|
Notation of 43edo
Because 43edo is a meantone system, this makes it easier to adapt traditional Western notation to it than to some other tunings. A# and Bb are distinct and the distance between them is one meride. The whole tone is divided into seven merides so this means we can use "third-sharps", "two-thirds-sharps", "third-flats", and "two-thirds-flats" to reach the remaining notes between A and B; notes elsewhere on the scale can be notated similarly.
Alternatively, a red-note/blue-note system (similar to that proposed for sixth-tones/36edo) can be used. (This is a different use of color than Kite's color notation.) Now we have the following sequence of notes, each separated by one meride: A, red A, blue A#, A#, Bb, red Bb, blue B, B. (Note that there are red flats and blue sharps, but no red sharps or blue flats, because the latter are enharmonically equivalent to simpler notes: blue Bb is actually just A#, for instance).
The diatonic semitone is four steps, so for the region between B and C (or, E and F), we can use: B, Cb, red Cb/blue B# (they are enharmonic equivalents), B#, and C. All of the notes in 43edo therefore have unambiguous names except for two: red Cb/blue B#, and red Fb/blue E#. It might also be possible to design special symbols for those two notes (resembling a cross between the letters B and C in the former case, and E and F in the latter).
If red Cb and blue B# (and red Fb/Blue E#) are instead forced to be distinct, but the requirement that all notes be equally spaced is maintained, then we end up with a completely unambiguous red-note/blue-note notation for 45edo, which is another meantone (actually, a flattone) system.