Abadd9 Chord

The major triad is A flat-C-E flat. Add B flat to make A flat-C-E flat-B flat. A ninth is the same pitch class as a second, counted an octave higher from the root. In the displayed chord, that higher placement leaves the triad clearly audible underneath.

B flat is the added ninth. The C natural must stay, because without the third you no longer have an add9 chord.

The root position and three inversions contain the same four note names:

Move the lowest note up an octave to hear each change. The order and bass shift, but the chord remains Abadd9. If another instrument supplies the bass, its note determines the full ensemble's lowest note; Chord Inversions explains how to write that.

No. Abadd9 has the four notes above and no seventh. Ab9 includes a minor seventh as well as the ninth. You can hear the difference by adding that seventh to Abadd9 while the other notes stay put. The plain 9 symbol implies a seventh; “add9” explicitly asks for the ninth without it. Add9 Chord compares the formulas across roots.

A sus2 chord replaces the third with a second. In Abadd9, the third C remains. Play the triad, add B flat, and then remove C. That last change moves you toward the suspended sound; it does not merely change the octave. The Suspended Second Chord explains the replacement.

Play the Ab major triad, add B flat, then return to the triad. Repeat with the added note an octave lower. The notes have the same names, but their spacing changes which part catches your ear. Keep the third present so the exercise remains about add9.