In the 60s and 70s, a remarkable number of remarkable artists transformed the samba tradition of Brazil into what came to be known as musica popular brasileira (MPB). Of all these artists--including such singers and songwriters as Ivan Lins, Gal Costa, Djavan, and of course the late Elis Regina--Milton Nascimento occupies a unique and even towering position. He is nothing less than the heart and soul of modern Brazilian music. His voice suggests his rural upbringing in its earthy mid-range, but when he propels it into falsetto, it becomes the sound of a newly arrived angel, all the better suited to the ethereal beauty of the melodies he composes. (Those melodies have captivated such Americans as Pat Metheny, Wayne Shorter, and Paul Simon, all of whom have taken pains to work with Milton live and on record.) He has resolutely championed the roots of his music by incorporating ancient folk traditions into his songs. He's taken that further on his latest album, Txai, which mingles new tunes with snippets of aboriginal chants and instrumental music to plead the case of the dwindling Amazon; because of its extramusical (though worthy) concerns, it's somewhat less satisfying than Milton's other albums. Reports say this emphasis on environmental matters has also stolen some of Milton's uplifting onstage fervor from his current tour. But Milton doesn't come through Chicago often, and that alone should draw even casual fans of MPB--induding anyone who owns Rhythm of the Saints (on which Milton briefly appears)--like the rain forest draws loggers. Wednesday, 8 PM, the Vic, 3145 N. Sheffield; 525-7793 or 902-1919.