Jim Hall and Bill Frisell, Hemispheres (ArtistShare, two CDs). An unprecedented collaboration between two guitarists whose sharply contrasting styles have more in common than you might suppose. The first disc is devoted to duets, the second to quartet performances featuring Scott Colley on bass and Joey Baron on drums. The fare varies from pop and jazz standards to challenging free improvisations in which Frisell lays down avant-garde “sonic landscapes” (his phrase) on top of which Hall soliloquizes with arresting eloquence. Rich, complex, involving (TT).