Extensions and Alterations
A thirteenth chord is not a wall of numbers. It is the same stack of thirds you already know, carried further up, and you rarely play all of it anyway.
- 5 to 7 notes
- 9, 11, 13
- thirds all the way up
which styles use it
- Jazz
- Neo-soul
- Film music
- Bossa nova
In short
Once a chord has a seventh, the next thirds up are called the ninth, eleventh and thirteenth. They are the second, fourth and sixth degrees of the scale an octave higher, renamed to show that a seventh is underneath. An alteration raises or lowers one of those notes by a half step, which sharpens the colour and usually increases the pull.
Extensions are the difference between a chord that is correct and a chord that sounds like a record. They add width without adding volume.
How to build it
- Add a seventh first
The numbers above nine only mean what they mean if a seventh is in the chord. Without one you are writing an add chord instead.
- Count in thirds, not in scale steps
From the seventh, the next third up is the ninth, then the eleventh, then the thirteenth. On a keyboard that is every other key, continuing the same pattern you started with.
- Leave notes out
A full thirteenth chord has seven notes and you have ten fingers and a bass player. Keep the third and the seventh, add the extension you want to hear, and drop the rest.
Where you run into this
- In jazz and neo-soul, where ninths and thirteenths are the normal texture rather than decoration.
- On dominant chords heading somewhere, where altered notes sharpen the pull.
- In film scoring, where an eleventh over a major chord gives that suspended, open sound.
The alterations side by side
C7 with one note moved:
- C7b9, darker and more urgent
- C7#9, the gritty one, a major and minor third in the same chord
- C7#11, bright and floating
- C7b13, tense and heavy