Opera house electronic libretto systems have begun to be used in some opera houses, including New York's Metropolitan Opera, Milan's La Scala, and the Crosby Theatre of The Santa Fe Opera, which provide two lines of text on individual screens attached to the backs of the seats so as to not interfere with the visual aspects of the performance. A subtle type of sound reinforcement called acoustic enhancement is used in some opera houses. Acoustic enhancement systems help give a more even sound in the hall and prevent "dead spots" in the audience seating area by "...augment[ing] a hall's intrinsic acoustic characteristics."
Metropolitan Opera House (Lincoln Center) premieres of operas, including John Corigliano's "The Ghosts of Versailles", Phillip Glass's "The Voyage" and the US premiere of Nico Muhly's "Two Boys" in 2013. When the Metropolitan Opera is on hiatus, the Opera House is home to the annual Spring season of American Ballet Theatre (ABT). It regularly hosts touring opera and ballet companies including the Kirov, Bolshoi, and the La Scala companies. In addition, the Met has presented recitals by Vladimir Horowitz, Renée Fleming, Kathleen Battle and others. Philip Glass's "Einstein on the Beach" was staged independently at the Met in 1976. Concerts by Barbra Streisand, The Who,