Modal Jazz utilizes a limited set of chords or pitches. For instance, instead of the one chord per beat in some bebop, modal may mean one song with only 1 or two chords throughout. This line is simply a collection of pitches within the d minor (with altered pitches) scale. If you would prefer, ignore the bass and create your own line. To paraphrase a great composer from an earlier time (no name so no copyright problems :)), With greater limis comes greater artistry. Try it. On a sidenote...I hope this is useful Adam