618edo
| ← 617edo | 618edo | 619edo → |
618 equal divisions of the octave (abbreviated 618edo or 618ed2), also called 618-tone equal temperament (618tet) or 618 equal temperament (618et) when viewed under a regular temperament perspective, is the tuning system that divides the octave into 618 equal parts of about 1.94 ¢ each. Each step represents a frequency ratio of 21/618, or the 618th root of 2.
618edo is consistent to the 7-odd-limit, but harmonic 3 is about halfway between its steps. Nonetheless, as every other step of 1236edo, 618edo is excellent in approximating harmonics 5, 7, 9, 11, 13, and 17, making it suitable for a 2.9.5.7.11.13.17 subgroup interpretation, where the equal temperament notably tempers out 2601/2600, 4096/4095, 5832/5831, 6656/6655, 9801/9800, and 10648/10647. With a reasonable approximation of 19, it further tempers out 2926/2925, 5985/5984, and 6175/6174.
Odd harmonics
| Harmonic | 3 | 5 | 7 | 9 | 11 | 13 | 15 | 17 | 19 | 21 | 23 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Error | absolute (¢) | +0.958 | +0.094 | +0.106 | -0.027 | +0.138 | +0.249 | -0.890 | -0.101 | -0.426 | -0.878 | +0.852 |
| relative (%) | +49 | +5 | +5 | -1 | +7 | +13 | -46 | -5 | -22 | -45 | +44 | |
| Steps (reduced) |
980 (362) |
1435 (199) |
1735 (499) |
1959 (105) |
2138 (284) |
2287 (433) |
2414 (560) |
2526 (54) |
2625 (153) |
2714 (242) |
2796 (324) | |
Subsets and supersets
Since 618 factors into 2 × 3 × 103, 618edo has subset edos 2, 3, 6, 103, 206, and 309. 1236edo, which doubles it, provides a good correction for harmonic 3.