Contributions to http://xenharmonic.wikispaces.com/ are licensed under a Creative Commons Attribution Share-Alike Non-Commercial 3.0 License.

Portions not contributed by visitors are Copyright 2018 Tangient LLC

TES: The largest network of teachers in the world

Portions not contributed by visitors are Copyright 2018 Tangient LLC

TES: The largest network of teachers in the world

Loading...

The interval 64/63, called

septimal commaorArchytas' commaor (in German)Leipziger Komma, is a superparticular ratio which equates 9/8 and 8/7 if tempered out and has the eighth square number as a numerator. It also equates 7/4 with 16/9, so that the just dominant seventh chord, 1-5/4-3/2-16/9, and the otonal tetrad, 1-5/4-3/2-7/4, are equated to the same chord when 64/63 is tempered out. Equal divisions of the octave tempering out 64/63 include 12, 15, 22, 27, 37, 49 and 59.The Archytas comma is a 7-limit comma with monzo | 6 -2 0 -1 >. It is

27.264092 cents in size.

It is similar to the Didymus or syntonic comma, 81/80, in that when it is tempered out it makes a stack of four fifths equal a major third (octave equivalent). In the case of 81/80, however, the major third is 5/4, while with the Archytas comma, the major third is 9/7. (Note that Porcupine, which tempers out 64/63, uses a minor tone as a generator and generally is considered to have 5/4 major thirds, so it doesn't depend on this equivalency.)

If you are using 9/7 major thirds, this also implies that the major third is split into two equal steps that represent both 9/8 and 8/7: If a stack of four fifths gets you to (octave-equivalent) 9/7, and a stack of two fifths gets you to 9/8, then the difference must be (9/7)/(9/8) = 8/7. The 8/7 and 9/8 intervals are equal, however, as a result of the generation process.

http://en.wikipedia.org/wiki/Septimal_comma