In music, a ninth (from Latin nona : “the ninth”) is an interval that spans nine pitches of a diatonic , heptatonic scale (e.g. c – d ' ). In a narrower sense, ninth can also mean the ninth degree of the scale.
The major ninth (a) comprises fourteen, the minor ninth (b) thirteen semitone steps. In counterpoint and harmonic movement, nons are usually treated like seconds. In the functional harmony, the ninth v. a. in the dominant seventh chord , in the jazz harmonic as a fourth third above the root (c).
A psychoacoustic effect comes into play with the ninth. The harmony of a major or minor ninth with the root is perceived as less unpleasant than the harmony of a major or minor second with the root. Although actually dissonant, a chord is formed from the root note, a pure fifth and a major ninth (fifth note chord) almost perceived as consonant when in Pythagorean (without using the Pythagorean wolf fifth), pure (only applies to the chord based on the root of the scale) or equal mood is played.
In connection with the partial tone series , for example in organ registers , the 9th partial tone is referred to as a ninth. This ninth has a frequency ratio of 9: 8 to the next lower octave. The ninth has a special position within the partial tones. It is not only the 9th partial of the root, but also the 3rd partial of the 3rd partial ("fifth") of the root. This is also a reason for the low dissonance effect when the major ninth in a chord sounds together with the root and fifth in Pythagorean , pure or equal tuning.
- Johann Gottfried Walther : Musical Lexicon [...]. Wolffgang Deer, Leipzig 1732, p. 444 ("... the second increased by one octave)"