When pianist Ursula Oppens moved here from New York to join the Northwestern University music faculty five years ago, composers all over town must have crossed their fingers. When Oppens premieres a piece, she sets the standard for all future interpreters, and many composers claim she elucidates their intentions better than they can themselves--an empathy that's earned her the nickname "Saint Ursula" in the new-music community. Even a short list of composers who've written for her--Elliott Carter, Frederic Rzewski, Joan Tower, Charles Wuorinen--reads like a who's who of postwar music, and her flexible keyboard technique allows her to sound equally convincing on Julius Hemphill's quasi-improvised riffs and Conlon Nancarrow's superficially simple but intricately structured canons. So far Oppens has premiered three works by locals during her tenure at Northwestern: a piece for two pianos by Patricia Morehead and two compositions by Amnon Wolman, a song cycle and a solo piano piece for two interfaced Disklaviers. This week she'll premiere number four, Humble Harvest, a two-part piano solo by longtime Northwestern professor M. William Karlins. The first movement is aggressive, hectic, and full of jazzy rhythms; the lyrical, meditative second movement, on the other hand, plays with and transforms motifs inspired by Beethoven's Piano Sonata no. 32. At a recital Tuesday, Oppens will perform Humble Harvest on a program with that very sonata, as well as no. 8 (Pathetique) and no. 18--the latest step in her project to record all 32 of Beethoven's piano sonatas. Though such a survey is a traditional rite of passage for a classical pianist, she's approached it in a highly idiosyncratic way: not only does she handle the sonatas like 20th-century pieces, but she also programs them with a contemporary selection to draw connections between Beethoven's work and the newer one. On Sunday, Oppens will preview Humble Harvest as part of Northwestern's six-hour NU New Music Marathon, which will also include a rare performance of Morton Feldman's 90-minute Crippled Symmetry by the California EAR Unit. Sunday, May 27, 4 PM, Mary and Leigh Block Museum of Art, Northwestern University, 1967 South Campus Dr., Evanston; 847-491-7315 or 847-491-5441. Tuesday, May 29, 7:30 PM, Pick-Staiger Concert Hall, Northwestern University, 1977 South Campus Dr., Evanston; 847-467-4000 or 847-491-5441.