I first heard violinist Nikolaj Znaider live in 2003, when he performed Schoenberg's concerto with the CSO under the baton of Daniel Barenboim. He was incredible. He made this difficult work, with all its technical challenges, graspable, playing with great emotion, musicality, and an intensity and purity of tone that made for an exceptional balance with the orchestra. Born in 1975, the Danish-Israeli violinist won first prize at the Carl Nielsen International Violin Competition when he was only 18, then went on to study briefly at Juilliard with Dorothy DeLay before traveling to Vienna to study the Russian style with Boris Kuschnir, who became his mentor. He recently released an outstanding CD of the Mendelssohn and Beethoven violin concerti, and he's playing the Mendelssohn on this program. On the CD he beautifully sculpts its abundant melodies and brings a no-holds-barred passion to the first movement, exquisite tenderness to the second, and sparkling virtuosity to the third. Even more remarkable are the subtler things he does. Many of his quieter sounds have a striking sense of intimacy, as when the violin enters at the very beginning and throughout the second movement. His transitions are also masterful--for instance, the way he alters his tone as he sits on a low note before the orchestra introduces the second theme--and he doesn't shy away from using portamento, the old-fashioned yet highly expressive sliding from one note into the next. The second half of the program consists of Mahler's Fifth Symphony, a massive work that's full of gorgeous melodies and luscious orchestration, shifting from the mournful to the serene to the joyful. Barenboim will conduct. See also Saturday and Sunday. Fri 10/14, 8 PM, Orchestra Hall, Symphony Center, 220 S. Michigan, 312-294-3000 or 800-223-7114, $17-$114.