The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped.
Bbaug7 is Bb, D, F# and Ab — Bb7 with the fifth raised a semitone.
It sounds strained and chromatic. The raised fifth is heard as a ♭13 sitting a semitone above where it is going, so the chord pushes harder than a plain dominant.

| Bb | D | F# | Ab |
|---|---|---|---|
| 1 | 3 | ♯5 | ♭7 |
Altered dominant — the pull of a 7, sharpened.
Also written Bb7#5, Bb+7 or Bb7(#5). The same chord either way; which spelling you meet depends on who wrote the chart.
The same operation one voice further down: the third voice from the top falls an octave and becomes the bass.
That leaves a bigger hole under the top three notes, so a string gets skipped: the muted string in the middle is the shape, not a mistake.
Bbaug7 has 9 of them, on strings 5-3-2-1 and strings 6-4-3-2, from open position up to the 13th — every inversion the chord has: Bb in the bass, D in the bass, F# in the bass and Ab in the bass. The one to learn first is the Bb shape at the nut.
5 of them sit on strings 5-3-2-1, so you can run the inversions up one set without changing strings — which is the whole reason to learn them as a family rather than as separate grips.
Start with 656x7x — low, at the 5th fret. None of the shapes for Bbaug7 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. None of them needs a barre. Together they cover the neck from the 1st fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x14132 | 1st fret | Bb, root position | F# | all fretted |
| 656x7x | 5th fret | Bb, root position | F# | all fretted |
| 6x677x | 6th fret | Bb, root position | F# | all fretted |
| x-x-8-11-9-10 | 8th fret | Bb, root position | D | all fretted |
| x-13-12-13-x-14 | 12th fret | Bb, root position | F# | all fretted |
The same notes rebuilt from scratch give 3 shell, 13 drop 2 and 3 open string voicings, each on its own page.
Tensions. A shell of Bbaug7, root, third and seventh, leaves a string free, and the tones that belong over it are the b9 (Cb), the 9 (C), the #9 (C#) and the #11 (E).
Bbaug7 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, Bbaug7 → Eb. 3 voices move by a semitone, and one note is common to both chords.
| In Bbaug7 | 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 |
Every note of Bbaug7 is in Bb whole tone and Bb altered.
Change one note of Bbaug7 and you have Bbmaj7#5 (the flat seventh becomes a major seventh), Bb7 (the sharp fifth becomes a fifth), Bb7b5 (the sharp fifth becomes a flat fifth), Bbalt (add the flat ninth), Bbaug (drop the flat seventh) or Bbaug9 (add the ninth).
Bbaug7 is an altered chord — a dominant seventh with its fifth or ninth moved. Altered dominant chords on every root.
On Bbaug7’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.