American baritone Thomas Hampson has one of the world’s great voices. Warm, rich, and velvety, it can range from a hushed quiver to the kind of ravishing high-voltage fortissimo needed for Wagner–he won a Grammy in 2003 for his recording of TannhŠuser. With the charisma of an opera star and the poetic soul of a lieder singer, he’s a riveting performer, able to fully inhabit a role and evoke its emotional depths. Hampson has long had an intense attachment to Mahler, deepened by a series of collaborations with Leonard Bernstein: together they performed and recorded many of Mahler’s vocal works during the last few years of the conductor’s life, including the early song cycle Lieder eines Fahrenden Gesellen (“Songs of a Wayfarer”), which Hampson will sing tonight with the Chicago Symphony Orchestra. A story of unrequited love told in four poems by the composer, it shares many qualities with his First Symphony–folk-inspired melodies, descriptions of nature, and orchestration that covers a breathtaking range of moods. Christoph Eschenbach conducts. The program also includes Bruckner’s Seventh Symphony. a 8 PM, Pavilion, Ravinia Festival, Green Bay & Lake Cook Rds., Highland Park, 847-266-5100, $10-$50. A –Barbara Yaross