Watch Bombuj. One morning, the late Karlheinz Stockhausen awoke from a dream that told him to take to the sky. Stockhausen envisioned four helicopters swirling in the clouds, with each of a quartet’s members tucked inside his own chopper, communicating through headsets, stringing away in sync to the rotor-blade motors. He immediately set forth to make that dream a reality. In 1995, Dutch film director Scheffer followed Stockhausen in the days leading up to the premiere performance of his Helicopter String Quartet in Amsterdam. The resulting film offers a rare glimpse of Stockhausen as he patiently dictates every agonizingly detailed measure to the Arditti Quartet.