Having covered Black Sabbath’s “Iron Man,” Stravinsky’s “Rite of Spring,” and, most recently, Ornette Coleman’s epochal “Science Fiction,” piano trio the Bad Plus returns to its own intricate explorations of song form and improvisation. (One of its albums is called “Prog,” after all.) It’s aided this time by saxophonist Joshua Redman. The knotty, gleaming structures often have hooky pop appeal (bassist Reid Anderson’s “Dirty Blonde,”), and the band can deliver an affecting ballad with brushes (“Lack the Faith But Not the Wine,” with lovely contrasting themes played by Redman and pianist Ethan Iverson). Iverson’s “Faith Through Error” kicks off with speedy, tightly wound arpeggios before becoming unhinged, then settling into an odd, minor-key march. There are few obvious jazz signifiers: no walking-bass swing, no Afro-Latin grooves, no blues. But Anderson’s “Silence Is the Question,” with its slow-build free-jazz rave-up over a long arc of development (13:31), is the kind of prog any Ornette fan could get behind. (Out Tuesday)