This transcription comes from the same album I wrote about last week, Bill Evans’ Interplay. Percy Heath gives us a lesson here on how to create a bass line that flows smoothly and logically through a set of chord changes. His melodious thud keeps great time, and he outlines the harmonic sequence using variations on a simple theme.
When written out with 8 measures per line, we can see how similar each 8-bar section is. Most sections start with the same three-note ascending line, and this pattern keeps reappearing throughout. See how often Percy starts a measure by walking from the root up to the third or from the fifth down to third. It’s about half the time! Beats 2 and 4 usually step up or down into a strong chord tone on a strong beat, and many chords are approached from a half step below. Upward chromatic motion gives a strong sense of resolution, as we can hear in bar 170, where the target note of Ab justifies Percy playing an E natural and F# on the strong beats while his bandmates comp a G altered chord.
This doesn’t mean he’s not listening to the band. In bar 130 he plays an A natural on beat 4 but cuts it short when he hears Bill Evans play an Ab, and the same happens in bar 180 when Freddie Hubbard plays a C over his B natural.
I wrote out the first six choruses, enough to get the idea of how this works.
I only wrote in the most basic version of the chord changes for reference here – of course Percy adds more nuance and motion to keep it interesting. For example, he treats almost every bar of G7 as a minor ii-V, playing a D on beat 1 and a G or B on beat 3.