Pianist and composer Bill Evans was famous for a playing style that was as big and orchestral as that of, say, Errol Garner, but more restrained and impressionistic (one might say that Evans was the Chopin to Garner’s Schumann). He was a natural fit for guitarist Jim Hall, whose tonal warmth obscured a restless and searching intellectuality. On both Undercurrent and the subsequent Intermodulation, the two conduct a musical conversation that was highly unusual for the time and remains a monument of thoughtful, exploratory jazz.