121/120
| Interval information |
undecimal seconds comma
Lologu comma
reduced
(Shannon, [math]\sqrt{nd}[/math])
In just intonation, 121/120, otherwise known as the biyatisma, or undecimal seconds comma, is a superparticular interval of around 14.4 cents which makes the difference between two undecimal neutral seconds of 11/10 and 12/11, between 11/8 and 15/11, and also the difference between 6/5 and two 12/11's.
Temperaments
Tempering out this comma in the 11-limit gives the rank-4 biyatismic temperament (→ Rank-4 temperament #Biyatismic (121/120)). Tempering it out in the 2.3.5.11 subgroup gives the rank-3 protomere temperament. See biyatismic clan for extensions of protomere. In such systems, 11/10 and 12/11 are equated, enabling biyatismic chords. This is similar to the more familiar tempering out of 81/80, which results in meantone and other temperaments, in which 10/9 is equated with 9/8. Equal temperaments in which 121/120 is tempered out include 15, 22, 29, 31, 46, 53 and others.
Etymology
The biyatisma was presumably named by Gene Ward Smith in 2010 since it seems this wiki was the place where it made its first appearance[1]. The name seems to come from maqam bayati, which features a neutral second. It is yet to be found out why it is spelt with an "i" instead of an "a".