Helikopter-Streichquartett

Completed in 1993, Stockhausen's Helikopter requires four helicopters with pilots, four sound technicians, four television transmitters, a 4 by 3 matrix of sound transmitters, an auditorium with four columns of televisions and four columns of loudspeakers, a sound projectionist with mixing console, a moderator, and airborne string quartet. This approximately thirty-minute long work begins with the introduction of the four string performers to the audience by the moderator who may also describe certain technical aspects of the piece. The performers head toward the four helicopters while the audience watches their approach over the video monitors in the auditorium. After embarking, the actions and sounds of each performer are carried back to the audio and video monitor stacks by 1: camera focused on close ups of the face, hands, bow, and instrument, 2: television transmitter, and 3: three microphones, including a contact mike on the bridge of the instrument, one directional mike for the vocal sounds, and a microphone mounted outside the helicopter which picks up the cyclic, rhythmic sound of the rotor blades. Once the players are settled inside the cockpits, the helicopters ascend for about five minutes, which is calculated from the beginning of the ignition of the turbines. During the ascent, the audience sees the earth through the glass, also sees the performer, and hears the sound of the rotors both from the outside microphone broadcast to the loudspeakers and acoustically above the auditorium. At the five-minute point, the instruments enter and the players produce steady pitches, one different tone per instrument, that are bowed at different specified rates (steady to fast tremolos). The pitches then gradually ascend and descend in glissandi with a consequent change in the rate of the bowing, making an effect that closely imitates or suggests the rhythmic heterodyning or fluttering of the helicopters' rotors. The frequently crossing pitch-lines and curves are notated in four different colors.

Once the instruments have begun playing, the helicopters fly in a circle within a radius of approximately six kilometers above the performance venue, individually varying the altitudes. At one extreme, if possible, they should fly high enough that the acoustic sound of the rotors will not reach the auditorium; or, at least, that the rotors' acoustic sound becomes far below that of the sound broadcast by the microphones into the loudspeakers.

The performers are kept in synchronization by a click-track that is transmitted to them. At various times, the performers in declarative tones call out numbers (in German or their native language)-1 to 5, 1 to 13, 1 to 7 to 1, etc., that test the sync among the players and also are correlated with lines and pitches by individual players. The structured sections (calculated to the tenth of a second) are the 'First formula cycle,' 'Second formula cycle,' and the 'Third formula cycle.' Toward the end of the piece, there are more obvious correlations between the strings that play chords attacked together. During the five-minute descent, various bowings on odd parts of the fingerboard produce harmonic sounds that imitate the buzzing phase sounds of the engines. After this spectacular visual and auditory onslaught, the cameras follow the players and pilots back to the auditorium. The moderator introduces the pilots and a general discussion ensues. Most days are programmed with at least three performances.