After recording four brilliant and ambitious albums as the Tin Hat Trio, founding member and accordionist Rob Burger left the band, leaving Mark Orton (guitars, banjo, piano) and Carla Kihlstedt (violin, viola, piano, vocals) to carry on with their delightful and off-kilter genre-bending experiments. And carry on they do with the considerable contributions of new members (and past collaborators) Ara Anderson (piano, trumpet), Ben Goldberg (clarinets), and Zeena Parkins (harp). All five are virtuosic multi-instrumentalists who specialize in creating moods and exploring subtleties — the music feels loose, yet without a wasted or unnecessary note. As difficult to classify as ever, the music incorporates elements of jazz, classical, bluegrass, klezmer, and assorted Americana, only with greater range and texture here as a result of the expanded instrumentation. There are spooky waltzes, melancholic marches, eerie minor-key melodies, and countless passages of sheer beauty and grace. Intoxicatingly strange and wondrous, The Sad Machinery of Spring is a moving and ingenious work likely to lodge itself deep within the imagination of listeners.