Bbaug9 is Bb, D, F#, Ab and C. Start with and raise the 5th from to . You’ll also see this chord written Bb9♯5 or Bb9(♯5).
Hear what that one-note change does by comparing with Bbaug9.
Only the 5th changes: F rises a half step to F♯. The other notes stay in place.
When Bbaug9 resolves to , that can rise another half step to .
Also written Bb9#5, Bb+9 or Bb9(#5).

Bbaug9 is a dominant with its tension raised, so it still points at — harder than a plain seventh does. A plain dominant has two voices a semitone from home; an altered one has four, because every altered tone is also sitting a semitone from a note of Eb. More voices leaning the same way is all "more tension" means here.
In a phrase:→→
The ii–V–I of Eb.
Voice by voice, Bbaug9 → . 3 voices move by a semitone, and one note is common to both chords. Those semitones are what the ear follows; the rest is the chord rearranging itself underneath.
| In Bbaug9 | Moves | In Eb |
|---|---|---|
| Bb, the root | stays where it is | Bb, the fifth |
| D, the major third | rises a semitone | Eb, the root |
| F#, the sharp fifth | rises a semitone | G, the major third |
| Ab, the flat seventh | falls a semitone | G, the major third |
| C, the ninth | falls a whole tone | Bb, the fifth |
Contains Bbaug9 and adds flat fifth.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.