A#9b5

Construction

Built from these intervals: 1-3-b5-b7-9.

The 3 and b7 form the tritone (the interval of six half steps) at the chord's core. The b5 replaces the natural 5, creating a second tritone between 1 and b5 -- an alteration (a chord tone lowered by a half step from its natural position) that doubles the instability. The 9 adds smoothness on top. 9b5 is 7b5 with an added 9. Five of the six whole tone scale pitches are present (1, 9, 3, b5, b7), giving the chord a floating, impressionistic character.

Harmonic Function

In Roman numeral analysis (uppercase = major, lowercase = minor):

• V9b5 -- altered dominant resolving to I, the b5 and 9 working together to create a sophisticated dominant color with chromatic tension.
• bII9b5 -- tritone substitution (replacing a V chord with a dominant whose root is a tritone away) with added warmth from the 9, softening the starkness of the plain bII7b5 approach.
• Whole tone dominant -- with five of six whole tone pitches present, this chord strongly implies the whole tone scale and its symmetrical, directionless quality.

Character

Floating and sophisticated. As a member of the altered dominant family, the 9 smooths the raw chromatic tension of 7b5, while the whole tone implications create a dreamy, impressionistic quality. Compare to 9#5: both are altered dominant 9th chords, but 9b5 compresses inward (the b5 lowers, creating diminished tension) while 9#5 stretches outward (the #5 raises, creating augmented brightness). This chord slides chromatically with elegance -- tension that shimmers rather than bites.

Related Sounds

These chords share the dominant core -- each changes the 5th or adds a different extension:

• 7b5 (1-3-b5-b7) -- the parent chord, without the 9th's smoothing effect; more stark tritone substitution sound
• 9 (1-3-5-b7-9) -- natural 5, standard dominant 9th without the chromatic edge
• 9#5 (1-3-#5-b7-9) -- #5 instead of b5, augmented brightness rather than diminished tension
• 7(b5,b9) (1-3-b5-b7-b9) -- b9 instead of natural 9, darker and more tense
• Pairs with the whole tone scale, which shares five of six notes with this chord

Voice Leading

Voice leading tracks how individual notes move from one chord to the next. The 9 adds an extra voice that can anchor or move by step, making the chromatic resolution smoother than the parent 7b5.

• V9b5 to I: The 3 moves up a half step to the root of I. The b5 moves down a half step to the root of I (or to the 3 in an open voicing). The b7 moves down a half step to the 3 of I. The 9 descends by step to the 5 of I. Nearly every voice has stepwise or chromatic motion.
• bII9b5 to Imaj7: Tritone substitution. The root of bII descends a half step to the root of I. The 3 of bII descends a half step to the 3 of I. The b5 of bII holds as the 5 of I (common tone). The b7 of bII ascends a half step to the root of I.
• ii7 to V9b5 to I: The 5 of ii is common with the 9 of V9b5, then descends by step to the 5 of I. The bass walks down by fifth while inner voices move chromatically.

These movements apply in any key -- the intervals are the same regardless of root.

Practice Seeds

Whole tone connection. Play 9b5, then the whole tone scale from the same root. Hear the scale inside the chord -- five of six pitches align, explaining the floating quality. This is the chord-scale relationship that gives 9b5 its impressionistic color.

Tritone sub with color. Compare bII7b5 to I versus bII9b5 to I. Hear how the 9 adds warmth and sophistication to the tritone substitution without losing its chromatic power.

Altered dominant comparison. Play 9, 9b5, and 9#5 on the same root. Distinguish the three dominant 9th colors -- natural 5, b5, #5 -- and how each alteration reshapes the chord's character from grounded to sliding to reaching.

Floating color. Use 9b5 over a static bass note, letting it linger without strong resolution. Experience its floating, whole-tone quality when used for color rather than strict dominant function -- this is its impressionistic side.