For DirectMusic to transpose a melody to a new chord, it needs to understand the relationship of the melody to its chord and scale. In our case, we base the bass line and melody off a C7 chord.
Add a Chord Track to the bass and melody Segments by right-clicking in the Segment window and selecting Add Track and Chord Track from the menus. Right-click on the first beat in the measure of the Chord Track and select Insert to insert a chord.
Figure 5-4: We define the chord and scale reference in the Chord Properties page. Here we use a C7 chord with a C Mixolydian scale.
On the bottom piano roll, set the chord to C7. Do this by clicking on the appropriate notes on the piano roll (C2, E2, G2, and Bb2). Now adjust the scale by changing the B natural to a Bb. Repeat this process for the second part as well.
You can copy the chord from the Chord Track and paste it in the other Segment's Chord Track, rather than resetting the notes manually.