121/120

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In Just Intonation, 121/120 (the biyatisma) is a superparticular interval of around 14.4¢ which makes the difference between two undecimal neutral seconds of 11/10 and 12/11. Temperaments in which 121/120 is tempered out include 15, 22, 29, 31, 46, 53 EDOs and others; in such systems, 11/10 and 12/11 are equated. This is in contrast 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. Along with being the difference between 11/10 and 12/11, 121/120 is the difference between 11/8 and 15/11, so that tempering out 121/120 allows for the dyadic triad which has intervals of 11/8, 11/8, and 16/15 (biyatismic triad).

See: Gallery of Just Intervals