641edo
| ← 640edo | 641edo | 642edo → |
641 equal divisions of the octave (abbreviated 641edo or 641ed2), also called 641-tone equal temperament (641tet) or 641 equal temperament (641et) when viewed under a regular temperament perspective, is the tuning system that divides the octave into 641 equal parts of about 1.87 ¢ each. Each step represents a frequency ratio of 21/641, or the 641st root of 2.
Theory
641edo is only consistent to the 5-odd-limit. Since both harmonics 7 and 11 are about halfway between its steps, and since harmonic 5 is also off by more than a third step, it can be used as a dual-5 dual-7 dual-11 temperament. Alternatively, it can be used as a 2.3.5.13.17.19 subgroup temperament, as it is consistent in the no-7 no-11 19-odd-limit.
To start with, consider the 641d val ⟨641 1016 1488 1799 2217 2372] in the 13-limit, which tempers out 625/624, 2200/2197, 4459/4455, 14641/14625, and 19712/19683. The alternative 641df val, ⟨641 1016 1488 1799 2217 2371], tempers out 676/675, 1001/1000, 19712/19683, 31213/31104, and 983125/979776. The 641ce val, ⟨641 1016 1489 1800 2218 2372], tempers out 676/675, 1001/1000, 6144/6125, 10985/10976, and 85294/85184.
Odd harmonics
| Harmonic | 3 | 5 | 7 | 9 | 11 | 13 | 15 | 17 | 19 | 21 | 23 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Error | Absolute (¢) | +0.073 | -0.666 | +0.909 | +0.146 | -0.928 | +0.034 | -0.593 | -0.119 | +0.147 | -0.890 | +0.743 |
| Relative (%) | +3.9 | -35.6 | +48.5 | +7.8 | -49.6 | +1.8 | -31.7 | -6.4 | +7.8 | -47.5 | +39.7 | |
| Steps (reduced) |
1016 (375) |
1488 (206) |
1800 (518) |
2032 (109) |
2217 (294) |
2372 (449) |
2504 (581) |
2620 (56) |
2723 (159) |
2815 (251) |
2900 (336) | |
Subsets and supersets
641edo is the 116th prime edo. 1282edo, which doubles it, gives a good correction to the harmonics 7 and 11.
Regular temperament properties
| Subgroup | Comma list | Mapping | Optimal 8ve stretch (¢) |
Tuning error | |
|---|---|---|---|---|---|
| Absolute (¢) | Relative (%) | ||||
| 2.3 | [1016 -641⟩ | [⟨641 1016]] | −0.0231 | 0.0231 | 1.23 |
| 2.3.5 | [24 -21 4⟩, [-56 -13 33⟩ | [⟨641 1016 1488]] | +0.0803 | 0.1474 | 7.87 |
Rank-2 temperaments
| Periods per 8ve |
Generator* | Cents* | Associated ratio* |
Temperaments |
|---|---|---|---|---|
| 1 | 254\641 | 475.507 | 320/243 | Vulture |
* Octave-reduced form, reduced to the first half-octave, and minimal form in parentheses if distinct