Modern jazz has reached such a high level of sophistication it is hard to imagine how it might increase in complexity. Instrumental technique, especially on piano and guitar, has become so advanced any further improvements would probably be largely imperceptible to listeners. Harmonic knowledge is exceptionally deep, the complexity of phrasing is advanced and the rhythmic complexity endlessly ornate. Jazz saxophonist and composer John Coltrane. So, why is it so often strangely unsatisf…