Cadd9 Chord

The major triad is C-E-G. Add D to make C-E-G-D. 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.

D is the ninth. Try C-E-G-D as a broken chord, then leave the D out to hear exactly what it adds.

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 Cadd9. If another instrument supplies the bass, its note determines the full ensemble's lowest note; Chord Inversions explains how to write that.

No. Cadd9 has the four notes above and no seventh. C9 includes a minor seventh as well as the ninth. You can hear the difference by adding that seventh to Cadd9 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 Cadd9, the third E remains. Play the triad, add D, and then remove E. 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 C major triad, add D, 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.