minor-13th / min13 / m13 / flat-13 / -13
A diatonic interval which traverses 12 steps in a diatonic scale, and covers a pitch distance bounded by 13 nominals inclusively, an octave plus an minor-6th.
The minor-13th became a common feature of blues and jazz harmony, especially during the bebop period in the late 1940s, particularly as an "extension" on top of a dominant-7th chord.
The 13th is the largest interval normally recognized by name in traditional harmony, since the method of building a chord in 3rds results in the double-octave (15th) when going beyond this, and thus returns to the root chord-member.
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