Saxophonist Chris Potter‘s new album, Imaginary Cities, came out on ECM last week. It’s his second release for the label, following 2013’s The Sirens, and like that one, it’s a concept album of sorts. That’s where the similarities end, though. The Sirens was an acoustic quintet disc, comprised of discrete pieces all based on themes from Homer‘s The Odyssey. This time, he’s expanded his long-running group the Underground (guitarist Adam Rogers, keyboardist Craig Taborn and drummer Nate Smith), turning it into the Underground Orchestra with the addition of vibraphonist Steve Nelson, two bassists (Scott Colley on upright and Fima Ephron on electric), and a string quartet composed of Mark Feldman and Joyce Hammann on violins, Lois Martin on viola and David Eggar on cello.