Recorded in 1965, Herbie Hancock’s “Maiden Voyage” was a revolutionary tune because it consisted almost entirely of sus chords. Studying “Maiden Voyage” is basically learning what options one can play on suspended chords. Sus chords fall in the family of dominant function but Sus chords are dominant 7th chords voiced with the notes 1,4,5,7 rather than 1,3,5,7. For C7sus, you can play the C Mixolydian (dominant) scale but if you emphasize or hover around the 3rd while the rhythm section is leaving the 3rd out and playing the 4th, you could sound pretty dissonant. A number of players choose to play the C Dorian (minor) scale over a C7sus. This way that problematic 3rd is a whole-step away from the 4th rather than a half-step.
The way Herbie voiced the opening D7sus in “Maiden Voyage”, was to play D (root) in the left hand and a C major triad in the right. If we take this line of thinking a little further and think of two major triads stacked on top of each other D & C we get a poly chord, or bi-tonality. I wrote an entire book devoted to exploring this concept in improvisation and an excerpt of it is here. There are a few books out there on the concept of chromatic-triadic playing and I encourage you to check them out. My book basically explores the relationship of two major triads a whole step apart and the different melodic lines than can be made with this information.
In a tune like “Maiden Voyage”, where the harmony consists entirely of sus chords, there is always the danger that the harmony will become too static and the music will lose its momentum. In a case like this, you might want to use a little dissonance and let taste be your guide. There is a lot of flexibility with Sus chords because while Dominant, ideas that fit in the major or minor realm work. Plus, the openness of their sound lends itself nicely to more angular lines as well as chromatic scalular ideas.
Another substitution that brings a little dissonance is the Sus b9 scale. This is like the Dorian (2nd mode) except where Dorian is derived from Major the Sus b9 is derived from the melodic minor scale.
So to sum up; a few options to think about when playing Sus chords are -(Click on the scales to enlarge)