Minor second

The musical interval of a half step, semitone, or minor second is the relationship between the leading tone and the first note (the root or tonic) in a major scale. It is the inversion of the Major seventh.

It can be produced by starting on a high note and playing the second below or by starting on a low note and playing the second above.

A minor second in just intonation corresponds to a pitch ratio of 16/15 or 1:1.0666, or various other ratios, while in an equal tempered tuning it is a ratio of 1:2^1/12 (approximately 1.059), or 100 cents, 11.731 centss flat of 16:15.

The minor second is considered the most dissonant interval after the tritone.