540/539
Interval information |
reduced
(Shannon, [math]\sqrt{nd}[/math])
540/539, the swetisma, is an unnoticeable comma in the 11-limit, equal to (15/11)/(7/6)2 or to (12/11)(15/14)/(7/6). In terms of commas, it is (99/98)/(121/120), (225/224)/(385/384), and (243/242)/(441/440).
Temperaments
Tempering out any two of 99/98, 121/120 and 540/539 will result in the third of the three being tempered, resulting in the rank-3 temperament big brother. More generally, tempering out 540/539 leads to swetismic temperaments and enables swetismic chords.
See Rank-4 temperament #Swetismic (540/539) for the rank-4 swetismic temperament. See Swetismic temperaments for a collection of rank-3 temperaments where it is tempered out.
Etymology
The swetisma was named by Manuel Op de Coul no later than 2004, after the Dutch ethnomusicologist Wouter Swets[1].