15/13: Difference between revisions

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In [[13-limit]] [[just intonation]], '''15/13''', the '''tridecimal semifourth''' is an interval measuring about 247.7¢. In the language of [[Margo Schulter]], 15/13 is an instance of an [[interseptimal]] interval, as it falls in an ambiguous zone between two septimal extremes – namely the large major second [[8/7]] and the small minor third [[7/6]]. (15/13)×([[13/10]]) = [[3/2]], which implies that 15/13 and 13/10 make a 3/2 perfect fifth. Thus you can make a [[List of root-3rd-P5 triads in JI|root-3rd-P5]] triad that goes 26:30:39, with a 15/13 ''inframinor third'' up from the root. When being used as type of second, it is given the name ''ultramajor second'' as it is even sharper than 8/7 which is often called a "supermajor second".  
In [[13-limit]] [[just intonation]], '''15/13''', the '''tridecimal semifourth''' is an interval measuring about 247.7¢. In the language of [[Margo Schulter]], 15/13 is an instance of an [[interseptimal]] interval, as it falls in an ambiguous zone between two septimal extremes – namely the large major second [[8/7]] and the small minor third [[7/6]]. (15/13)×([[13/10]]) = [[3/2]], which implies that 15/13 and 13/10 make a 3/2 perfect fifth. Thus you can make a [[List of root-3rd-P5 triads in JI|root-3rd-P5]] triad that goes 26:30:39, with a 15/13 ''inframinor third'' up from the root. When being used as type of second, it is given the name ''ultramajor second'' as it is even sharper than 8/7 which is often called a "supermajor second".  
== Approximation ==
== Approximation ==
{{Interval_Edo_Approximation | 15/13}}
{{Interval edo approximation|15/13}}
== See also ==
== See also ==
* [[26/15]] – its [[octave complement]]
* [[26/15]] – its [[octave complement]]

Revision as of 13:12, 3 November 2025

Interval information
Ratio 15/13
Factorization 3 × 5 × 13-1
Monzo [0 1 1 0 0 -1
Size in cents 247.7411¢
Name tridecimal semifourth
Color name 3uy2, thuyo 2nd
FJS name [math]\displaystyle{ \text{A2}^{5}_{13} }[/math]
Special properties reduced
Tenney norm (log2 nd) 7.60733
Weil norm (log2 max(n, d)) 7.81378
Wilson norm (sopfr(nd)) 21

[sound info]
Open this interval in xen-calc

In 13-limit just intonation, 15/13, the tridecimal semifourth is an interval measuring about 247.7¢. In the language of Margo Schulter, 15/13 is an instance of an interseptimal interval, as it falls in an ambiguous zone between two septimal extremes – namely the large major second 8/7 and the small minor third 7/6. (15/13)×(13/10) = 3/2, which implies that 15/13 and 13/10 make a 3/2 perfect fifth. Thus you can make a root-3rd-P5 triad that goes 26:30:39, with a 15/13 inframinor third up from the root. When being used as type of second, it is given the name ultramajor second as it is even sharper than 8/7 which is often called a "supermajor second".

Approximation

Edo approximations for 15/13 (247.74 ¢)
≤ 80edo, relative error ≤ 10%
Edo Step size Cents (¢) Absolute error (¢) Relative error (%)
5 1\5 240.00 -7.74 -3.23
10 2\10 240.00 -7.74 -6.45
15 3\15 240.00 -7.74 -9.68
19 4\19 252.63 +4.89 +7.74
24 5\24 250.00 +2.26 +4.52
29 6\29 248.28 +0.53 +1.29
34 7\34 247.06 -0.68 -1.93
39 8\39 246.15 -1.59 -5.16
44 9\44 245.45 -2.29 -8.38
48 10\48 250.00 +2.26 +9.04
53 11\53 249.06 +1.32 +5.81
58 12\58 248.28 +0.53 +2.58
63 13\63 247.62 -0.12 -0.64
68 14\68 247.06 -0.68 -3.87
73 15\73 246.58 -1.17 -7.09

See also