2.5 subgroup: Difference between revisions

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== MOS scales ==
== MOS scales ==
As it is a [[rank-2]] system, stacking 5/4 with octave-reduction can produce [[MOS scale]]s, just like how Pythagorean tuning famously produces a version of the pentatonic, diatonic and chromatic scales. An important structural feature of the 2.5 subgroup is that [[5/4]]<sub>3</sub> = [[125/64]], which is only a diesis ([[128/125]]) short of an octave. This means that the cube root of 2, or the familiar [[3edo]]/[[12edo]] major third, is a decent approximation of 5/4. It also means that most small MOSes generated by the 2.5 subgroup are of the form 3L ''x''s, and are extremely [[hard]] (high L:s ratio) which makes them difficult to use.
As it is a [[rank-2]] system, stacking 5/4 with octave-reduction can produce [[MOS scale]]s, just like how Pythagorean tuning famously produces a version of the pentatonic, diatonic and chromatic scales. An important structural feature of the 2.5 subgroup is that [[5/4]]<sub>3</sub> = [[125/64]], which is only a diesis ([[128/125]]) short of an octave. This means that the cube root of 2, or the familiar [[3edo]]/[[12edo]] major third, is a decent approximation of 5/4. It also means that most small MOSes generated by the 2.5 subgroup are of the form 3L ''x''s, and are extremely [[hard]] (high L:s ratio) which makes them difficult to use. It takes all the way up to a 31-tone MOS (28L 3s) to break out of the 3L ''x''s chain, which corresponds to how [[31edo]] is the smallest EDO to have an approximation of 5/4 in-between just 5/4 and the cube root of 3.


The non-trivial MOS scales that are produced are: [[1L 2s]], [[3L 1s]], [[3L 4s]], [[3L 7s]], [[3L 10s]], [[3L 13s]], [[3L 16s]], [[3L 19s]], [[3L 22s]], [[3L 25s]], [[28L 3s]], [[28L 31s]], [[59L 28s]], [[59L 87s]], etc.
The non-trivial MOS scales that are produced are: [[1L 2s]], [[3L 1s]], [[3L 4s]], [[3L 7s]], [[3L 10s]], [[3L 13s]], [[3L 16s]], [[3L 19s]], [[3L 22s]], [[3L 25s]], [[28L 3s]], [[28L 31s]], [[59L 28s]], [[59L 87s]], etc.