Inmusic, aninth is acompoundinterval consisting of anoctave plus asecond.

Like the second, the interval of a ninth is classified as adissonance incommon practicetonality. Since a ninth is an octave larger than a second, itssonority level is considered less dense.^[1]

Amajor ninth is a compound musical interval spanning 14semitones, or an octave plus 2 semitones. If transposed into a single octave, it becomes a major second or minor seventh. The major ninth is somewhat dissonant in sound.

Some commontransposing instruments sound a major ninth lower than written.These include thetenor saxophone, thebass clarinet, thebaritone/euphonium when written intreble clef, and thetrombone when written in treble clef (British brass band music).

When baritone/euphonium or trombone parts are written inbass clef ortenor clef they sound as written.

Aminor ninth (m9 or -9) is a compound musical interval spanning 13 semitones, or 1 semitone above an octave (thus it isenharmonically equivalent to an augmented octave). If transposed into a single octave, it becomes a minor second or major seventh. The minor ninth is rather dissonant in sound,^[2] and in European classical music, often appears as asuspension.Béla Bartók wrote a study in minor 9ths for piano. The fourthmovement (anintermezzo) ofRobert Schumann'sFaschingsschwank aus Wien is constructed to feature prominent notes of themelody a minor ninth above the accompaniment:

^{[citation needed]}Alexander Scriabin'sPiano Sonata No. 9, 'Black Mass' is based around the interval of a minor ninth, creating an uncomfortable and harsh sound.^{[citation needed]} Several ofIgor Stravinsky's works open with a striking gesture that includes the interval of a minor 9th, either as a chord:Les Noces(1923) andThreni(1958); or as an upward melodic leap:Capriccio for Piano and Orchestra(1929),Symphony in Three Movements(1946), andMovements for Piano and Orchestra(1960).

Anaugmented ninth is a compound musical interval spanning 15 semitones, or 3 semitones above an octave. Enharmonically equivalent to a compound minor third, if transposed into a single octave, it becomes a minor third or major sixth.

See:Dominant seventh sharp ninth chord.

Three types of ninth chords may be distinguished: dominant (9), major (M9), and minor (m9).^[3][4] They may easily be remembered as the chord quality of the seventh does not change with the addition of the secondscale degree,^[3] which is a major second in bothmajor and minor, thus:

0 4 7 t + 2 =dominant seventh + ninth = dominant ninth chord0 4 7 e + 2 =major seventh + ninth = major ninth chord0 3 7 t + 2 =minor seventh + ninth = minor ninth chord

The dominant ninth (V₉) is a dominant seventh plus a major or minor ninth.^[5]

• Augmented octave
• Augmented unison