Inverse | neutral third |
---|---|

Name | |

Other names | - |

Abbreviation | n6 |

Size | |

Semitones | ~8½ |

Interval class | ~3½ |

Just interval | 18:11^{[1]} or 13:8^{[2]} |

Cents | |

12-Tone equal temperament | N/A |

24-Tone equal temperament | 850 |

Just intonation | 853 or 841 |

A **neutral sixth** is a musical interval wider than a minor sixth ^{ⓘ} but narrower than a major sixth ^{ⓘ}. Three distinct intervals may be termed neutral sixths:

- The
*undecimal neutral sixth*has a ratio of 18:11 between the frequencies of the two tones, or about 852.59 cents.^{ⓘ} - A
*tridecimal neutral sixth*has a ratio of 13:8 between the frequencies of the two tones, or about 840.53 cents.^{[3]}This is the smallest neutral sixth, and occurs infrequently in music, as little music utilizes the 13th harmonic.^{ⓘ} - An
*equal-tempered neutral sixth*is 850 cents, a hair narrower than the 18:11 ratio. It is an equal-tempered quarter tone exactly halfway between the equal-tempered minor and major sixths, and half of an equal-tempered perfect eleventh (octave plus fourth).^{ⓘ}

These intervals are all within about 12 cents of each other and are difficult for most people to distinguish. Neutral sixths are roughly a quarter tone sharp from 12 equal temperament (12-ET) minor sixths and a quarter tone flat from 12-ET major sixths. 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.

A neutral sixth can be formed by subtracting a neutral second from a minor seventh. Based on its positioning in the harmonic series, the undecimal neutral sixth implies a root one minor seventh above the higher of the two notes.

The pitch ratio 13:8 (840.53 cents) is the ratio of the thirteenth harmonic and is notated in Ben Johnston's system as A^{13}♭. In 24-ET is approximated by A. This note is often corrected to a just or Pythagorean ratio on the natural horn, but the pure thirteenth harmonic was used in pieces including Britten's *Serenade for tenor, horn and strings*.^{[4]}