The Old High German word gougalon is the origin of the modern verb gaukeln, which describes the performance of medieval street entertainers. In her eponymous ensemble piece, Unsuk Chin employs contemporary musical means to imagine “Scenes from a Street Theater,” inspired by a blend of hypermodern urbanity and the labyrinthine, history-rich alleyways of 1960’s Seoul during the composer’s childhood. Matthias Pintscher and the Boulez Ensemble combine Chin’s “imaginary folk music” with Schoenberg’s “accompaniment” to an equally imaginary film scene and the suggestive polyrhythms of Ligeti’s Piano Concerto, featuring Barenboim-Said Akademie alumna Julia Hamos as the soloist. Mozart’s C-minor Serenade opens the program.