C#madd9 is C#, E, G# and D#. It adds the to without adding a 7th. includes the flat 7th as well.
The and are a half step apart. Let both notes ring over a held minor chord. Rock writers often use that close interval.
Also written C#m(add9), C#min(add9) or C#-add9.
A folk-rock phrase in a minor mode can come home through E and B to C#madd9. The ♭VII’s third is the ninth of the i, so it holds over and colours the landing.
Listen for: A half step down to the ♭VII’s third, which then holds as the ninth. On the plain minor chord it falls a whole step to the root.
Heard in“John Barleycorn”
In which keys. Every note of C#madd9 belongs to C# minor, E major, Ab minor and B major.
Contains C#madd9 and adds fourth, flat thirteenth and flat seventh.
Contains C#madd9 and adds fourth, sixth and flat seventh.
Contains C#madd9 and adds fourth, flat thirteenth and major seventh.
Contains C#madd9 and adds fourth, sixth and major seventh.
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.