
When I start a new vocal jazz arrangement, I find it helpful to:
1)Write out the chord changes.
2)Write out a “stylized” melody.
A “stylized melody” is one that changes the rhythms (and sometimes pitches) based on how I would sing the tune if I were performing it as as a soloist. By stylizing it, I’ve already made the first steps to creating a unique arrangement by changing what’s on the page or heard in the original recording.

Ranges
To the left is a general idea of vocal ranges for each part. Of course, there is some wiggle room depending on your ensemble’s voices and the type of sound that you are trying to obtain.
As a rule, avoid writing harmony in small intervals between parts in lower registers. This causes the sound to be “muddy.”
What notes can I use in a chord?
Jazz chords will almost always have four notes. The third and seventh must always be present to establish the chord quality. Everything else is color! Often, the root of the chord will be omitted because a bass guitar would be covering that note already. Though, you might choose to add it to achieve a certain timbre.
In a straight-up major chord, like shown to the right, the 6 or the 9 can be added to add richness. You could even have both at the same time. Here, I’ve given examples of chords in both open voicing (spread larger than an octave) and closed voicing (contained within an octave).


Minor chords must contain a b3 and a b7. There are instances where you might see a natural 7. If you play it, you might immediately think of spy movie!
Color notes that are effective are the 9th and/or the 11th. Sometimes you might see a 6 tucked in there as well. Again, I’ve given you examples of chords in both open and closed voicings.
Dominant (7) chords often give you the most creative choices. Again, you must have the third and the b7.
When adding color notes, I like to think of them as alterations to the 5th or the 9th because you wouldn’t use the natural 5th or 9th along with its alteration. If you lower the 5th a half-step, raise it a half-step, or raise it a whole step, you get the #11, b13, or 13 respectively. If you lower the 9th a half-step or raise it a half-step, you get the b9 or #9 respectively. You can have multiple alterations if you want!


Let’s go back to my arrangement of “Gotta Be This or That” and analyze what I did. You’ll notice above that I use various textures for variety. As this is the beginning of the tune, I don’t want to do too much too soon. So, I start with some lines that switch between 2-part harmony and 4-part closed voicings. I made a point to put the 4-part harmony on “wrong” and “dark” in the first line to emphasize those words. Then, when we hit that longer note on “sure,” I broaden the chord with 4-part open voicing. You can see an instance of me stylizing the melody by changing the rhythm of “you might.” To tie up the entire phrase , I return to two-part harmony in the last measure. You’ll see that all of my harmonies are based on my written-in chords changes.

Let’s analyze what comes next in the example above. For a change, I vary the texture again by now adding some counterpoint between the women and men’s voices. Once we reach the second half of the phrase in m.15, the parts unite and a lush minor 9 chord highlights Mr. Crosby himself. As kind of a throwaway joke, I give Frank a tritone. Where there was 2-part harmony on the first “gotta be this or that,” we now have full-on 4-part harmony to wrap up the entire section. You can see that I made very deliberate choices to have each section build upon the last so the tune feels like there is natural growth occurring. Again, I used the chord changes to guide my harmony choices.
Harmonizing the melody is what makes jazz stand out from classical music or contemporary a cappella arrangements. Phil Mattson once told me that jazz harmonies are built from the top down whereas classical harmonies are built from the bottom up. Contemporary a cappella arrangements generally have a soloist with the rest of the singers providing backup textures and harmonies like you would hear in a band. By prioritizing the melody in your vocal jazz arrangement, you will more successfully emulate the style. Good luck!