Nexus comma
| Interval information |
nexisma nexuma
The nexus comma, otherwise known as the nexisma, or- in the earliest sources where this comma is named- the nexuma, is an 11-limit unnoticeable comma with a ratio of 1771561/1769472 and a value of approximately 2 cents. It is the sum of the schisma and the parimo, the difference between the rastma and the Alpharabian comma, and the amount by which a stack of three 128/121 Alpharabian diatonic semitones falls short of a 32/27 minor third. Tempering it out leads to the joining of the 11-limit and the 3-limit, a fact which, in light of the importance of both p-limits, lends itself to this temperament being dubbed the "nexus temperament"- the source of this comma's names. While the importance of the 3-limit is generally accepted (see Pythagorean tuning, circle of fifths, FJS, Helmholtz-Ellis notation), it can be derived mathematically that the 11-limit is an excellent basis for quartertones in terms of ratio simplicity, and the 11-limit can be shown to host a clear sequence of intervals in which every other member is the octave complement of what is effectively a stack of diatonic semitones (see Alpharabian tuning). For a list of temperaments that temper out the nexuma, see nexus family.