D#7(#5,b9)

Construction

Built from these intervals: 1-3-#5-b7-b9.

The #5 replaces the natural 5 with an augmented interval that pulls upward. The b9 sits a half step above the root, adding dark, dissonant tension that pulls downward. 7(#5,b9) is 7#5 with an added b9. An alteration is a chord tone raised or lowered by a half step from its natural position. Here the two alterations move in opposite directions -- the #5 reaches up while the b9 presses down -- creating contrary motion (voices spreading apart) that distinguishes this chord from the other three double-altered dominants.

Harmonic Function

In Roman numeral analysis (uppercase = major, lowercase = minor), this is one of four double-altered dominants -- chords that combine two alterations on a dom7 foundation. The four are 7(b5,b9), 7(b5,#9), 7(#5,b9), and 7(#5,#9). This one pairs the only raised fifth with a lowered ninth:

• V7(#5,b9) in minor -- altered dominant resolving to i. The #5 is enharmonically the b3 of the target minor chord (same pitch, different name), so it holds as a common tone (a note shared between chords). The b9 resolves down a half step to the 5th.
• V7(#5,b9) in major -- the #5 resolves up a half step to the 3rd of I, the b9 resolves down a half step to the 5th of I. Contrary motion: the two altered tones spread apart into the tonic.
• V7(#5,b9) as altered scale chord -- pairs with the altered scale (seventh mode of melodic minor, containing all possible dominant alterations), which includes both #5 and b9

Character

Bright yet dark. The #5 stretches upward with augmented brightness while the b9 pulls downward with minor-key shadow -- contradictory forces coexisting in a single harmony. This contrary motion is the chord's defining quality: it expands outward rather than compressing inward, creating a wider registral spread at the moment of resolution. Compare to 7(b5,b9): that chord funnels both alterations in the same downward direction, while 7(#5,b9) spreads its tension in two directions at once.

Related Sounds

These chords share the dominant core -- each modifies one or two elements:

• 7#5 (1-3-#5-b7) -- parent chord, augmented dominant brightness without the b9's darkness
• 7b9 (1-3-5-b7-b9) -- natural 5, dark ninth without augmented brightness
• 7(b5,b9) (1-3-b5-b7-b9) -- lowered fifth instead of raised, both alterations compress inward rather than spreading
• 7(#5,#9) (1-3-#5-b7-#9) -- same #5 but raised ninth instead, aggressive rather than dark, with two common tones to i7
• Pairs with the altered scale (seventh mode of melodic minor), which contains both #5 and b9

Voice Leading

Voice leading tracks how individual notes move from one chord to the next. The #5 resolves upward and the b9 resolves downward, both by half step -- voices spreading outward from the chord.

• V7(#5,b9) to I: The #5 moves up a half step to the 3rd of I. The b9 moves down a half step to the 5th of I. The 3 rises a half step to the root. Two altered tones spread apart into the tonic chord.
• V7(#5,b9) to i: The #5 (enharmonically the b3 of i) holds as a common tone. The b9 drops a half step to the 5th of i, and the 3 rises a half step to the root. The #5 becoming the b3 of i is a uniquely smooth connection to minor.
• iiø7 (half-diminished -- minor 7th with a b5) to V7(#5,b9) to i: The contrary motion of the V chord creates an outward-spreading resolution. The b9 of V arrives from the b5 of ii, then resolves down a half step to the 5th of i.

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

Practice Seeds

Contrary motion. Play V7(#5,b9) and resolve to I. Listen for the #5 moving up while the b9 moves down at the same time -- that outward spreading is what sets this chord apart from the other double-altered dominants.

Common tone to minor. Play V7(#5,b9) resolving to i, and listen for the #5 holding as the b3 of the target chord. This enharmonic common tone (same pitch, different name in each chord) is why the chord connects so naturally to minor.

Altered scale connection. Play 7(#5,b9), then the altered scale (seventh mode of melodic minor) from the same root. Both the #5 and b9 are scale tones -- hearing the scale inside the chord links harmony to melody.

Compare #5 pairs. Play 7(#5,b9) then 7(#5,#9) on the same root. Same augmented fifth, different ninths. The b9 adds shadow; the #9 adds aggression. The fifth stays bright in both -- only the ninth changes the mood.