Alterations

altered extensions (e.g., b9, #11) are most common on dominant seventh chords
for the V (including secondary V) chord, choose b9 and/or b13 (aka b6)
in a chorale voicing, use b9 in place of 9; b13 in place of 5 or 6
for V chords resolving to minor chords, this is almost mandatory
for other chords, alterations are optional
for dominant seventh chords that occur in other contexts, choose #11 (aka #4)
#9 may also sound good in some cases (sounds like b3, so it creates a bluesy sound)
#11 can be used in conjunction with any of these (9, b9, #9, 5, 6, or b13)
#11 can also be used on major seventh chords
less commonly, #5 may also be used on major sevenths

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