Father–3 equivalence continuum/Godtone's approach
The augmented–chromatic equivalence continuum is a continuum of 5-limit temperaments which equates a number of 128/125's (augmented commas) with the chroma, 25/24. As such, it represents the continuum of all 5-limit temperaments supported by 3edo.
This formulation has a specific reason: 128/125 is significantly smaller than 25/24, so that it makes sense to equate some number of 128/125's with 25/24, but because 25/24 = (25/16)/(3/2), this has the consequence of clearly relating the n in (128/125)n = 25/24 with how many 5/4's are used to reach 3/2 (when octave-reduced):
If n = 0, then it takes no 128/125's to reach 25/24, implying 25/24's size is 0 (so that it's tempered out), meaning that 3/2 is reached via (5/4)2.
For integer n > 0, we always reach 25/24 via (25/16)/(128/125)n because of (128/125)n ~ 25/24 by definition, meaning that we reach 3/2 at 3n + 2 generators of ~5/4, octave-reduced.
The just value of n is log(25/24) / log(128/125) = 1.72125… where n = 2 corresponds to the Würschmidt comma.
| n | Temperament | Comma | |
|---|---|---|---|
| Ratio | Monzo | ||
| −2 | Smate (14 & 17c) | 2048/1875 | [11 -1 -4⟩ |
| −1 | Father (5 & 8) | 16/15 | [4 -1 -1⟩ |
| 0 | Dicot (7 & 10) | 25/24 | [-3 -1 2⟩ |
| 1 | Magic (19 & 22) | 3125/3072 | [-10 -1 5⟩ |
| 2 | Würschmidt (31 & 34) | 393216/390625 | [17 1 -8⟩ |
| 3 | Magus (43 & 46) | 50331648/48828125 | [24 1 -11⟩ |
| 4 | Supermagus (55 & 58) | 6442450944/6103515625 | [31 1 -14⟩ |
| 5 | Ultramagus (67 & 70) | 824633720832/762939453125 | [38 1 -17⟩ |
| … | … | … | … |
| ∞ | Augmented (12 & 15) | 128/125 | [-7 0 3⟩ |
| n | Temperament | Comma | |
|---|---|---|---|
| Ratio | Monzo | ||
| -1/2 | Yo (2c & 5c) | 10/9 | [1 -2 1⟩ |
| 1/2 | Wesley (26 & 29) | 78125/73728 | [13 2 -7⟩ |
| 3/2 | Ditonic (50 & 53) | 1220703125/1207959552 | [-27 -2 13⟩ |
| 5/2 | Novamajor** (77 & 80) | 19791209299968/19073486328125 | [41 2 -19⟩ |
| 7/2 | 3 & 101 | (36 digits) | [55 2 -25⟩ |
* This corresponds to the denominator of 2 implying that 3 must be reached in a half-integer number of ~5/4's.
** Note that "novamajor" (User:Godtone's name) is also called "isnes"; both names are based on the size of the generator being around 405 cents, but "isnes" was discovered as a point in the continuum while "novamajor" was discovered as one temperament in the fifth-chroma temperaments.
If we approximate the JIP with increasing accuracy, (that is, using n a rational that is an increasingly good approximation of 1.72125...) we find these high-accuracy temperaments:
| n | Temperament | Comma | |
|---|---|---|---|
| Ratio | Monzo | ||
| 5/3 | Mutt (84 & 87) | mutt comma | [-44 -3 21⟩ |
| 7/4 | 3 & 118 | (42 digits) | [61 4 -29⟩ |
The simplest of these is mutt which has interesting properties discussed there. In regards to mutt, the fact that the denominator of n is a multiple of 3 tells us that it has a 1\3 period because it's contained in 3edo. The fact that the numerator is 5 tells us that 25/24 is split into 5 parts. From (128/125)n = 25/24 we can thus deduce that each part is thus equal to ~cbrt(128/125) = (128/125)1/3, so that ~5/4 is found at 1\3 minus a third of a diesis, so that ~125/64 is found at thrice that.
The 3 & 118 microtemperament is at n = 7/4. Its generator is approximately 397 ¢ so that four generators reaches 5/2, corresponding to the denominator of 4. The number of generators of ~(5/2)1/4 needed to find prime 3 is thus four times the result of plugging n = 7/4 into 3n + 2 , which is 3(7/4) + 2 = 21/4 + 8/4 = 29/4, that is, 29 generators.
Also note that at n = −2⁄3, we find the exotemperament tempering out 32/27.