Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top.
Bbaug9 is Bb, D, F#, Ab and C — Bb7 with the fifth raised and the natural ninth added on top.
It sounds bright, tense and slightly unreal. Raising the fifth leaves no semitone in the lower half of the chord, which is where the whole-tone flavour comes from.

| Bb | D | F# | Ab | C |
|---|---|---|---|---|
| 1 | 3 | ♯5 | ♭7 | 9 |
Altered dominant — dominant pull with a whole-tone colour.
Also written Bb9#5, Bb+9 or Bb9(#5). The same chord either way; which spelling you meet depends on who wrote the chart.
Root, third and seventh. The third and seventh, the guide tones, are what make the chord major, minor or dominant, so the fifth can go: it says nothing the symbol needs.
Three notes means a spare string, which is the real point. Put a tension on it.
Bbaug9 has 8 of them, on the middle four strings, the bottom four strings, the top four strings, strings 5-3-2-1 and strings 6-4-3-2, from open position up to the 13th — all in one inversion, so the bass note never moves. The one to learn first is the Bb shape at the nut, which is the easiest grip here.
Start with xx6778 — no barre. 1 of the 7 shapes here sits in open position. 4 of the 7 need a barre. Together they cover the neck from the 1st fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x10112 | open position | Bb, root position | F# | barred |
| 434334 | 3rd fret | Ab, 3rd inversion | Ab | barred |
| 65657x | 5th fret | Bb, root position | F# | all fretted |
| 6x6778 | 6th fret | Bb, root position | C | all fretted |
| xx6778 | 6th fret | Ab, 3rd inversion | C | all fretted |
| 10-11-10-11-11-10 | 10th fret | D, 1st inversion | D | barred |
| x-13-12-13-13-14 | 12th fret | Bb, root position | F# | barred |
The same notes rebuilt from scratch give 14 rootless and 1 open string voicings, each on its own page.
Tensions. A shell of Bbaug9, root, third and seventh, leaves a string free, and the tones that belong over it are the #11 (E).
Bbaug9 is a dominant with its tension raised, so it still points at Eb — harder than a plain seventh does, because the altered tones sit a semitone from where they are going.
Voice by voice, Bbaug9 → Eb. 3 voices move by a semitone, and one note is common to both chords.
| 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 |
Every note of Bbaug9 is in Bb whole tone.
Change one note of Bbaug9 and you have Bbalt (the ninth becomes a flat ninth), Bbaug7 (drop the ninth), Bb9 (the sharp fifth becomes a fifth) or Bb9b5 (the sharp fifth becomes a flat fifth).
Bbaug9 is an altered chord — a dominant seventh with its fifth or ninth moved. Altered dominant chords on every root.
On Bbaug9’s sound and use this page follows Mark Levine, The Jazz Theory Book (Sher Music, 1995). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.