Beginning today, Sept. 18. Daniel Felsenfeld will lead a series of 12 sessions on Mahler and Schoenberg being offered by the 92nd Street Y School of Muisc. It examines two of the most important composers of the 20th century, both of whom happed to be born Jewish. Mahler’s work summed up the Romantic period and marked its closure; Schoenberg, following Mahler’s direction, created many of the musical techniques that define the 20th century. Both men converted in their lifetimes. Schoenberg returned later in life to Judaism. The class examines their works, their biographies and thei culture that surrounded them The course is taught by composer and music writer Daniel Felsenfeld. 2-3pm. Cost: $320.