Chord Extensions
A chord extension is adding an extra interval to an existing chord, e.g., C (C, E, G) C7 (C, E, G and Bb) or Cm (C, Eb, G) Cm6 (C, Eb, G and A). There are also extension intervals which are placed into the next octave, e.g., 9. The ninth is the same note as the 2nd except it is usually found in a chord an octave higher, e.g., C9 (C, E, G and D)
A list of all commonly used extensions and their respective lower octaves is shown in the following diagrams. Each of these intervals can be considered as major intervals, unless otherwise indicated with sharp or flat signs, except the 7th which is always a minor seventh. If used, the major seventh is indicated as a maj7. The most common alteration of the extensions and their respective lower octaves are listed here.
b9 = minor 2nd + octave (only used on Dom7b9 chords)
#9 = augmented 2nd (minor 3rd) + octave (only used on Dom7#9 chords)
#11 = augmented 4th + octave (mostly used on Maj7(#11) or Dom7(#11)chords)
b13 = minor 6th (augmented 5th) + octave (mostly used on Dom7b13 chords)
Extensions are normally used to add some extra color to a chord to make it sound more interesting. They are more commonly played by chord instruments like guitar or keyboard or melody/solo instruments.
As a Bass player they have to be used more carefully and sparse because the bass instrument is the lowest and should establish the foundation of a chord which is the root note mainly. Extension notes are good to use as passing notes.
