81/70

Interval information

Ratio	81/70
Factorization	2-1 × 34 × 5-1 × 7-1
Monzo	[-1 4 -1 -1⟩
Size in cents	252.6804¢
Name	septimal ultramajor second
Color name	rg2, rugu 2nd
FJS name	[math]\displaystyle{ \text{M2}_{5,7} }[/math]
Special properties	reduced
Tenney norm (log2 nd)	12.4691
Weil norm (log2 max(n, d))	12.6797
Wilson norm (sopfr(nd))	26
[sound info]
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81/70, the septimal ultramajor second is a 7-limit interseptimal ratio of about 253 cents. It is sharp of a major second 9/8 by a septimal quartertone 36/35, sharp of a supermajor second 8/7 by a syntonic comma 81/80, and flat of a subminor third 7/6 by a sensamagic comma 245/243.

Notice it is also flat of the just minor third 6/5 by a subminor second 28/27. For this fact it is useful in the sensamagic dominant chord where it functions as a dissonance yet to be resolved up to the minor third. The canou temperament targets this progression and uses it as one of the generators.

Approximation

It is near-perfectly approximated by 19edo (4\19), with an error of 0.05 cents, and hence equally well done by the enneadecal temperament.

See also

• 140/81 – its octave complement
• 35/27 – its fifth complement
• Gallery of just intervals