A 'ninth' may refer to:

 

· A harmonic or melodic interval of an octave and a second.

 

· The tone at the upper limit of such an interval.

 

· A type of chord that spans a ninth between its root and topmost note. There are both ninth chords and added ninth chords.

 

Major ninth.

 

Interval of a ninth

A ninth is a compound interval consisting of an octave plus a second, i.e., an interval between two pitches that are nine degrees of the diatonic scale apart: C-d, E-f, A-b, etc. A major ninth consists of seven whole steps, a minor ninth consists of six whole steps and a half step.

 

Added ninth chords

The added ninth is an added tone chord, as distinct from an extended chord. Remember that a ninth is a second plus an octave. When the second note of a scale is added to the major triad built on that scale's tonic note, it produces a chord made up of the first, second, third, and fifth notes. Normally, it would be called a "second chord", but, to avoid confusion with second inversions and with chords in which the second note actually replaces the third, it is referred to by its extended name – the "ninth". Because it is not an extended chord, this is made clear by using the prefix "added".

 

The second note can be added to minor triads as well as to majors. In both cases, added ninths are clear, strong chords – due to the relationship of the I, II, and V. In fact the added ninth is often played without the third note. The minor added ninth features the most dissonant interval of all – the one semitone minor second – between the 2nd/9th note and the flatted third. Yet, used creatively, this interval can produce simple chords of startling beauty, especially on the guitar.

 

Ninth chords

A ninth chord is an extended chord, consisting of a seventh chord to which has been added a ninth. Ninth chords are therefore five-note chords (octave + seventh + ninth). They come in three varieties – dominant, major, and minor ninth – made by adding the extra note to the four-note dominant seventh, major seventh, and minor seventh. All the ninths consist of four intervals of a third stacked on top of one another, so they can be thought of as two triads, the top one anchored to the top note of the bottom one. The sound produced by varying the five notes in a ninth chord depends on which notes are omitted or doubled, and on how the notes are spaced.

 

Altered ninth chords

Within the structure of a ninth chord each of the four notes above the root (3rd, 5th, 7th, and 9th) may be altered: the 3rd note may be either major or minor in relation to the root; the 5th may be diminished, perfect, or augmented; the 7th may be diminished, minor, or major; and the 9th may be minor, major, augmented. A simple mathematical calculation shows that these permutations can be produce 27 different ninth chords.

 

These chords can be grouped into the three families of dominants, minors, and majors. The dominant family offers the greatest number of altered ninths. They can be divided into those that feature only one altered note (the 5th or 9th) and those that feature two altered notes (the 5th and the 9th).

 

When the 9th note is altered, the chord is named according to the four-note sevenths chord that forms its foundation. The altered ninth is written after this as either -9 or +9. The term "minor ninth" and "major ninth" are generally reserved for ninth chords built on minor sevenths and major sevenths.

 

The 6th note of a scale can also be included in these ninth chords, However, if the 5th replaces the 7th, the chord is called a "six nine" chord, and, if the 6th, 7th, and 9th are all present, the chord is called a thirteenth.