Septimal tritone
A septimal tritone is a tritone that involves the factor seven.
There are two that are inverses. The lesser septimal tritone is the musical interval with ratio 7:5. The greater septimal tritone, is an interval with ratio 10:7. They are also known as the sub-fifth and super-fourth, or subminor fifth and supermajor fourth, respectively.
The 7:5 interval is equal to a 6:5 minor third plus a 7:6 subminor third.
The 10:7 interval is equal to a 5:4 major third plus an 8:7 supermajor second, or a 9:7 supermajor third plus a 10:9 major second.
The difference between these two is the septimal sixth tone .
12 equal temperament and 22 equal temperament do not distinguish between these tritones; 19 equal temperament does distinguish them but doesn't match them closely. 31 equal temperament and 41 equal temperament both distinguish between and closely match them.
The lesser septimal tritone is the most consonant tritone when measured by combination tones, harmonic entropy, and period length.
Depending on the temperament used, "the" tritone, defined as three whole tones, may be identified as either a lesser septimal tritone, a greater septimal tritone, neither, or both.
