Bossa for Betty Carter for jazz ensemble was written with the intent of exploring various timbres in the ensemble much the way Betty would alter the tone of her voice while shaping phrases during an improvisation.
The harmonic qualities were inspired from a masterclass at the Berklee School of Music during the first Harmony Conference they held many years ago. During a masterclass with Richie Bierach a questions was asked regarding his harmonic thinking. He had just sent us the listeners to what sounded like uncharted harmonic waters with variation upon variation on the opening bars to “Round Midnight”. His suggestion was to create your own harmonic vocabulary based on density. With each harmonic entity, or chord, you create, he suggested that you give it a density number from one to ten. After creating a collection of these, build a piece that pushes the from one level to another increasing or decreasing tension as you see fit. Set theory should open up possibilities when studying 20th century atonal music for the creation of some of your own harmonic entities or sets.
Try dropping your hands at random on the keys of the piano with no particular intervallic structure preplanned in your mind, or your hands, and see what you discover. Do you like what you hear? Is it hard to describe? If you intend on keeping this strucutre or chord, give it a density level of dissonance from 1-10 and continue building your new harmonic vocabulary.
Sometimes there are several ways to view your new synthetic harmonies. They may look like an extracted set from traditional harmonies or be apart of a particular mode. Maybe it is perhaps a bitonal harmony or some kind of harmony over a unrelated bass note . It may appear your structure is sort of like a major chord but just not include the third or an altered dominant without the third or seventh present. This leads to the next question of how you intend to represent your chords to the rhythm section or the soloist. Many times if I have a particular mode in mind, or implied by the harmony, I will write out the mode for the soloist and rhythm section. There maybe more than one choice of modes or jazz scales available to the soloist. I then decide for the soloist what sound I have in mind be including the mode or new synthetic scale in place of traditional chord changes. If I wish to give more freedom, listing the scale with no suggested mode should be enough for the soloist.
Each of these new structures can be explored further by inversion to generate new ways of generating voice leading from one structure to another in your progression. A pseudo modulation or series of substitute harmonies appear by incorporating such inversions. In these cases the general modal sound referenced does not change but the implied direction of the bass made it sound as if the progression has traveled somewhere new. Extending or compressing the lengths of any one or set of these new substitute harmonies will allow the form to develop in an unpredictable way.
A more subtle way of thinking about modes, synthetic scales, density or dissonance levels is to think in terms of brightness and darkness of each new sonorites you develop. I highly recommend Modal Jazz Composition and Harmony Vol 1 and 2 by Ron Miller published by Advance Music. Volume 1 has The Collated Order Of All Constructed Modes listed on p 122. There are 35 altogether. With this chart you can plan out modal movement with harmonies that move from one level of brightness or darkness to another.