31 Equal Temperament - Interval Size

Interval Size

Here are the sizes of some common intervals:

interval name size (steps) size (cents) midi just ratio just (cents) midi error
harmonic seventh 25 967.74 Play 7:4 968.83 Play −1.09
perfect fifth 18 696.77 Play 3:2 701.96 Play −5.19
greater septimal tritone 16 619.35 10:7 617.49 +1.87
lesser septimal tritone 15 580.65 Play 7:5 582.51 Play −1.86
undecimal tritone, 11th harmonic 14 541.94 Play 11:8 551.32 Play −9.38
perfect fourth 13 503.23 Play 4:3 498.04 Play +5.19
septimal narrow fourth 12 464.52 Play 21:16 470.78 play −6.26
tridecimal major third 12 464.52 Play 13:10 454.21 Play +10.31
septimal major third 11 425.81 Play 9:7 435.08 Play −9.27
undecimal major third 11 425.81 Play 14:11 417.51 Play +8.30
major third 10 387.10 Play 5:4 386.31 Play +0.79
tridecimal neutral third 9 348.39 Play 16:13 359.47 play −11.09
undecimal neutral third 9 348.39 Play 11:9 347.41 Play +0.98
minor third 8 309.68 Play 6:5 315.64 Play −5.96
septimal minor third 7 270.97 Play 7:6 266.87 Play +4.10
septimal whole tone 6 232.26 Play 8:7 231.17 Play +1.09
whole tone, major tone 5 193.55 Play 9:8 203.91 Play −10.36
whole tone, minor tone 5 193.55 Play 10:9 182.40 Play +11.15
greater undecimal neutral second 4 154.84 Play 11:10 165.00 −10.16
lesser undecimal neutral second 4 154.84 Play 12:11 150.64 Play +4.20
septimal diatonic semitone 3 116.13 Play 15:14 119.44 Play −3.31
diatonic semitone, just 3 116.13 Play 16:15 111.73 Play +4.40
septimal chromatic semitone 3 77.42 Play 21:20 84.47 Play −7.05
chromatic semitone, just 2 77.42 Play 25:24 70.67 Play +6.75
lesser diesis 1 38.71 Play 128:125 41.06 Play −2.35
undecimal diesis 1 38.71 Play 45:44 38.91 Play −0.20
septimal diesis 1 38.71 Play 49:48 35.70 Play +3.01

The 31 equal temperament has a very close fit to the 7:6, 8:7, and 7:5 ratios, which have no approximate fits in 12 equal temperament and only poor fits in 19 equal temperament. The composer Joel Mandelbaum (born 1932) used this tuning system specifically because of its good matches to the 7th and 11th partials in the harmonic series.

This tuning can be considered a meantone temperament. It has the necessary property that a chain of its four fifths is equivalent to its major third (the syntonic comma 81:80 is tempered out), which also means that it contains a "meantone" that falls between the sizes of 10:9 and 9:8 as the combination of one of each of its chromatic and diatonic semitones.

Read more about this topic:  31 Equal Temperament

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