What does "(add 9)" mean when written on sheet music?

add a 9th interval to your chord

What does that mean? Or rather, how do I achieve that?

Take the ninth note of the scale and add it to the root.
For example, the ninth of a C note or chord is the next D up the keyboard.

ok, thanks.

Yes…just to clarify lefteh’s great response-whatever the chord is (if its being spelled by letter as in a lead sheet, or if it’s by degree number in more theoretical instances), take the root of that chord, then determine the 9th degree-it’s one octave up plus 1 whole step (Octave plus a Major 2nd to be exact).

In some degrees of the scale it creates an augmented interval on “top”, which enhances the chord color as in various 7th chords (9th chords are an extension of the 7th chord in a sense). Used a lot in Jazz and in Romantic-era “classical music.” On a tonic or root chord (the root of the key the song’s in), it creates a feeling of suspension when it is unresolved (when it doesn’t resolve back to the tonic).

It’s interesting to compare (add9) to (add2) or (sus2) chords. There might be a significant difference. I’ll explain this with reference to open position guitar chords. Look at a regular D chord. If you open up the high E string you got a D(sus2). The “sus” implies that the third degree (F#, normally on the first string) is not played and the (2, E) is substituted for the third. Now consider the same D chord with the E note on the second fret of the fourth string. From the highest string down, the notes are F#, D, A, E. This would be an (add2) because the complete major triad is still being played.

Now lets consider a C major chord in first position. If you add the D note on the second string, third fret, I’d call this a C(add9) because again, you have the full C triad sounding on the 5th, 4th and 3rd strings. If you open up the fourth string of a regular C chord it’s more accurately a C(sus2) or C(add2) depending upon whether and E notes are sounded.

Oh. And if you add the D note to a C7 chord it’s definitely a C9 as chords named with numbers higher that 7 are implied 7th chords with compound intervals added to them.

Having fun? Let’s go back to the D(add2) played with E on the fourth string. You could also call this an E11 or an A6(sus4). Any chord with four or more different notes has at least two different root names.

I could go on, but I better stop.

if you count the notes in a scale you will find that 8 is the octave and 9 would be the same as 2:)