Although recent years have found cornetist Rob Mazurek working with larger ensembles like the Exploding Star Orchestra, he returns on his latest Delmark recording, Sound Is, to the smaller group mode where he’s arguably done his best work. The quintet Mazurek assembled for Sound Is reunites him with several colleagues from his old Chicago home base (he’s lived in Brazil for several years now), some going all the way back to his late ‘90s roots in the jazz-fusion group Isotope 217. The presence of former Isotope members John Herndon (now better known as drummer/percussionist for Tortoise) and Matthew Lux ensures that the quintet frequently re-imagines the traditional roles of its instrumentation—on many of the album’s 14 tracks, Lux’s electric bass works in tandem with Josh Abrams’ acoustic bass in entirely unexpected ways. Mazurek’s cornet and shimmering vibraphone work by Jason Adasiewicz blend into the overall fabric of sound created by the dual basses and drums—sometimes enhanced by electronic treatments and overdubs—to create a complete and well-sequenced work that’s as simultaneously beautiful and challenging as anything in Mazurek’s discography.