The smaller of the two diatonic intervals which encompass 6 degrees of the of the diatonic scale. The minor-6th is composed of 3 tones (i.e., whole-tones) and 2 diatonic semitones, and is one chromatic semitone smaller than the major-6th.
____ minor-6th _____ | | C D E F G A B C s t t t s m2 M2 M2 M2 m2 minor-6th = 3t + 2s = 3(t-s) + 5s = 3(M2) + 2(m2) = 3(+1) + 5(m2)
Thus, the minor-6th contains 3 chromatic semitones and 5 diatonic semitones (or equivalently, 3 augmented-primes and 5 minor-2nds). In 12-edo, the minor-6th encompasses 8 equal semitones.
Narrowing the minor-6th by one more chromatic semitone results in the diminished-6th.