The rapt blend of two acoustic guitars and an occasional vocal transforms this first full-length collaboration between emerging jazz virtuoso Julian Lage and Punch Brothers’ Chris “Critter” Eldridge into an exceptional, boundary-defying musical encounter. Overseen by another young and up-and-coming artist, The Milk Carton Kids’ Kenneth Pattengale, Avalon offers an essential homage to the broad tapestry of American music, from country, bluegrass and gospel to jazz, Tin Pan Alley and various traditional trappings in between. Likewise, the duo taps into various musical masters—Jimmie Rodgers, Norman Blake and George and Ira Gershwin among them—augmenting those standards with songs of their own composition. Eldridge, seldom a singer in his day job, does an admirable job reinterpreting homespun homilies like “Mean Mother Blues,” “Any Old Time” and “Ginseng Sullivan,” but it’s his winsome reading of the Gershwins’ “Someone to Watch Over Me” that reflects the duo’s true charms.