The challenge here is to be melodically inventive using only the notes from a particular mode, e.g. the respective Dorian mode for a Dm7 and Ebm7 chord. In reality, after a few verses, many musicians use alternate modes and chromatic notes to generate tension, and sustain interest, in a modal jazz song.
You may think, this sounds much easier than playing a jazz song with lots of chord and key changes. It is technically easier, but you have to be more melodic and creative to pull it off. For instance, you can't fall back on your favourite licks on a ii-v-i chord progression.
For example, if Ebmin7 was on the lead sheet you first choice mode would Eb Dorian, Amaj#4 your first choice mode would be A Lydian, B7 you would use B Mixolydian and so on.
To begin with, it may be easier to think of the modes in relation to their parent Major scale. So D Dorian, is C Major starting on D (2nd note of C Major), E Phrygian is C Major starting on E (3rd note of C major), F Lydian is C Major starting on F (4th note of C major), etc.
Key based improvisation
In a jazz song with a key centre, the aim is to "play the changes" and improvise smoothly over a series of fast changing chords. To simplify this task, a musician will often break down a song into a number of different keys. For example, on the Miles Davis track "Tune Up" the first section can be interpreted as D, C, and Bb major: *
