Harmonisma
| Ratio | 10648/10647 |
| Factorization | 23 × 3-2 × 7-1 × 113 × 13-2 |
| Monzo | [3 -2 0 -1 3 -2⟩ |
| Size in cents | 0.16259536¢ |
| Name | harmonisma |
| Color name | 3uu1o3r-2, Thuthutrilo-aru comma |
| FJS name | [math]\text{m}{-2}^{11,11,11}_{7,13,13}[/math] |
| Special properties | superparticular, reduced |
| Tenney height (log2 nd) | 26.7565 |
| Weil height (log2 max(n, d)) | 26.7566 |
| Wilson height (sopfr (nd)) | 78 |
| Harmonic entropy (Shannon, [math]\sqrt{nd}[/math]) |
~1.19846 bits |
| Comma size | unnoticeable |
| open this interval in xen-calc | |
10648/10647, the harmonisma, is a no-5's 13-limit unnoticeable comma of about 0.1626 cents. It is equal to (16/13 × 11/9)/(14/11 × 13/11). In terms of other commas, it is (352/351)/(364/363), (3025/3024)/(4225/4224), (4096/4095)/(6656/6655), or (9801/9800)/(123201/123200).
Temperaments
Tempering out this comma in the full 13-limit gives the rank-5 harmonismic temperament. Equal temperaments where this comma is tempered with very high accuracy, such as 764edo, will have an interval corresponding to a "sharp fifth" of (ideally) 706.7 to 706.9 cents, corresponding to the range of fifths from 13/11 × 14/11 (→ 182/121) on the lower end and 11/9 × 16/13 (→ 176/117) on the higher end, and this interval is not mapped to 3/2. However, such temperaments are generally very precise, so 224edo, 270edo and 311edo offer slightly more manageable tunings. For less accurate temperaments still, 10648/10647 is notable as a comma of parapyth.
The harmonisma, 10648/10647, plays a striking role in George Secor's 29-tone high tolerance temperament of 1975, the first temperament in the High Tolerance Temperament family. In this tuning, the fifth at 703.579 cents produces an augmented second (+9 fifths) at a just 63/52 (9/8 × 14/13), or a diminished seventh (-9 fifths) at 104/63, which exceeds three 13/11 thirds by a harmonisma. The 63/52 exceeds the Pythagorean augmented second, 19683/16384 (a 32805/32768 schisma larger than 6/5), by the secorian comma, 28672/28431. Likewise 104/63 is narrower than the Pythagorean 32768/19683 by 28672/28431.
The secorian comma is made up of (896/891 × 352/351) or in other words (352/351 × 364/363 × 352/351), and is thus a harmonisma smaller than (352/351)3. In 29-HTT, each 13/11 is thus a third of a harmonisma or 0.054 cents wider than just. Secor's HTT fifth of 703.579 cents, or precisely (504/13)1/9 or wide by 1/9 of a secorian comma, would thus need to be 1/9 harmonisma larger at 703.597 cents to produce a just 13/11, a temperament of the fifth by (352/351)1/3.
Another manifestation of the harmonisma in 29-HTT is the tuning of 11/9 at 347.353 cents, a third of a harmonisma narrow. Here 7/4 is just, with the spacing between the relevant chains of fifths in a subset of 29-HTT which served as a prototype for parapyth temperament at 58.090 cents, as compared with the 91/88 spacing which would produce a just 7/4 if the regular major sixth were at a just 22/13. But it is a third of a harmonisma narrow, and the spacing consequently a third of a harmonisma greater.
As it happens, the difference between 11/9 and 13/11 is 121/117, a harmonisma greater than 91/88 (e.g. 22/13 vs. 7/4). Since the tempered 13/11 is a third of a harmonisma greater than just, and the spacing a third of a harmonisma greater than 91/88, this leaves 1/3 of the harmonisma difference between 91/88 and 121/117 unaccounted for, the amount by which 11/9 is narrow.
In parapyth, generally, the spacing can represent four ratios, whose differences show the four commas tempered out: 33/32 (53.273¢) and 91/88 (58.036¢) at 364/363 (4.763¢) apart ; 91/88 and 121/117 at 10648/10647 (0.163¢) apart; 121/117 and 28/27 (62.961¢) at 364/363 (4.763¢) apart; and the smallest and largest intervals among these represented by the parapyth spacing, 33/32 and 28/27 at 896/891 (9.688¢) apart. Thus 896/891 = (352/351 × 364/363), and also (364/363 × 10648/10647 × 364/363). A difference of 352/351 (4.925¢) or (364/363 x 10648/10647) occurs between 121/117 and 33/32, and between 28/27 and 91/88.
Here, for example 33/32 is 4/3 vs. 11/8; 91/88 is 22/13 vs. 7/4; 121/117 is 13/11 vs. 11/9; and 28/27 is 9/8 vs. 7/6.
Subgroup: 2.3.5.7.11.13
| [⟨ | 1 | 0 | 0 | 0 | 1 | 3 | ], |
| ⟨ | 0 | 1 | 0 | 0 | 0 | -1 | ], |
| ⟨ | 0 | 0 | 1 | 0 | 0 | 0 | ], |
| ⟨ | 0 | 0 | 0 | 1 | 1 | 1 | ], |
| ⟨ | 0 | 0 | 0 | 0 | -2 | -3 | ]] |
- mapping generators: ~2, ~3, ~5, ~7, ~44/39
Optimal ET sequence: 41, 46, 58, 80, 87, 103, 121, 149, 161, 183, 190, 224, 270, 494, 684, 764, 954, 1178, 1236, 1448, 1506, 2190, 2684, 4190, 4771, 6691, 6961, 7455, 9645, 17100
Etymology
The harmonisma was named by Margo Schulter in 2002 in honor of the harmoniai of Kathleen Schlesinger.