Neutral third

A neutral third is a musical interval wider than a minor third  play  but narrower than a major third  play , named by Alois Hába. Three distinct intervals may be termed neutral thirds:

These intervals are all within about 12 cents and are difficult for most people to distinguish by ear. Neutral thirds are roughly a quarter tone sharp from 12 equal temperament minor thirds and a quarter tone flat from 12-ET major thirds. In just intonation, as well as in tunings such as 31-ET, 41-ET, or 72-ET, which more closely approximate just intonation, the intervals are closer together.