Another synchronizing procedure uses a special track of multi-channel tape for cues that the instrumentalist hears through headphones. An early example is Ramon Sender's Desert Ambulance (1964) for amplified accordion, stereo tape, and light projection. Sender used a special three-channel tape: two channels contained the stereo sounds heard by the audience, and the third, heard only by the accordionist, contained pitches, timing cues and spoken instructions. p.293

The Chamberlain is probably the most unusual live-performance invention. It consists of a series of magnetic tape loops, with each loop actuated by a corresponding key on a traditional keyboard. The sounds to be heard from the Chamberlain can be from any source, and are recorded by the performer in advance. A dramatic example of the use of the Chamberlain is the introduction to Ramon Sender's Desert Ambulance (1964). p.325