What is the composition about? It is an image of flight experienced as music. Imagery of flight is a recurrent feature of Stockhausen's music and images specifically of propellor-like rotation involving impulsive textures can be found in a number of earlier Stockhausen compositions, and also in works by other composers with which Stockhausen is known to be familiar.

A helicopter besides being an instrument of flight is also a machine that produces a certain kind of sound. In Helikopter-Streichquartett the musical action in its simplest form consists of four helicopters taking off, hovering, and landing, in the course of which rotors are set in motion, starting off as a rhythm and rising to a pitch, stabilizing on the hovering pitch, then descending to the ground, parking, and shutting off allowing the rotors to descend in pitch, slow to a rhythm once again, then to a stop. What the audience experiences in essence is the transformation of a regular beating or pulsing sensation into a tone of variable pitch and back again, in association with the idea and imagery (via television) of flying, like a tourist excursion.

Why choose a string quartet? The work was commissioned for the Arditti Quartet, so that part of the instrumentation is a given. Why the helicopters? That is the interesting question. Not 'what do I write for string quartet' but 'how can the sound of a string quartet be incorporated into the sound and gesture vocabulary of LICHT and in particular Mittwoch aus LICHT?

Let me be clear. This is a work of exceptional strength and vitality, of stunning simplicity and absolute integrity. It is as hard as nails - or as hard as an ammonite. Like an ammonite it is an aesthetically beautiful image of a process that is both natural and universal, the sound of the four helicopters providing a mechanical-impulsive shell as it were, and the fricative motions of the four string players a softer living acoustic tissue that in the long run adds its own nacreous gleam to the hard outer carapace.

At the same time, let's not be squeamish either. Stockhausen has no particular fondness for the violin family. Here he takes an almost perverse delight in creating conditions that are the opposite of what a string quartet relies on to make harmonious music. First, he separates the four players so they can neither see nor hear one another. Second, he limits the tonal range of these aristocrats of emotional expression to strident and abrasive tremolandi. Third, he has them strapped awkwardly into the passenger seats of hovering aircraft that are not only unstable but dangerous platforms considering the value of these instruments and their owners. It would be interesting to learn if the Arditti Quartet chose to perform on their regular instruments (if so, how would we tell?), and who covered the insurance. But the views of the players are not to be found anywhere in the liner notes.

Stockhausen says that the work came to him in a dream. A dream can be a way of avoiding discussion. The work comes fully-formed as if in a vision. By definition there is nothing more to say about it. There is no other explanation.

However when Stockhausen says 'dream' he is making a coded allusion to the tradition of dream in artistic creation, and in particular to the surrealists and other persecuted 'degenerate artists' he has made it his mission to rehabilitate. We therefore look to the literature of twentieth-century art for some basis or rationale for a music of helicopters in action, the most striking being Luigi (LU-IGI) Russolo's Futurist Manifesto (see my article A is for Anthiel) in which, speaking of a new music based on the sounds of machines, he refers specifically to 'certain noises produced by rotary motion [offering] a complete ascending and descending chromatic scale by merely increasing and decreasing the speed of the motion' and that 'to fix the pitch of noises [is designed] not to take away from them all the irregularity of tempo and intensity that characterizes their vibrations, but rather to give definite gradation of pitch to the stronger and more predominant of these vibrations'.

There are a number of issues arising from the use of helicopter imagery. The imagery of flight is one, the imagery of rotation is another, and Stockhausen's history of pulsating sounds, especially in relation to acceleration in time, yet another. A rich tapestry of musical and theoretical associations quickly begins to emerge.

Rotational motion and the sound associated with it is a feature not only of Stockhausen's music but one that connects with other times and cultures. In the movie Crocodile Dundee II you may remember a moment in the outback where the hero retreats to the top of a hill while his New York girlfriend stays alone by the campfire. All of a sudden out of the silence a weird whirring sound is heard rising and falling in speed and pitch. It is the sound of a primeval instrument called a bull-roarer, a shaped piece of wood at the end of a cord that produces a musical sound as you spin it around. This instrument is not only a form of bush telephone used by native Australian aborigines to keep in touch, it is also a means by which ancient cultures made contact with the spirit world, the domain the aborigines call 'dream time'. (The Australian composer John Anthill has composed a ballet suite, Corroborree, for orchestra and bull-roarer.)

Rotational motion is also the operational principle of the medieval model of the music of the spheres, the idea that the planets and stars in their orbits generate musical pitches that together combine to make a celestial harmony. The message underlying the music of the spheres is that rotational motion in both the macro (celestial) and micro (musical pitch) domains signifies stability. A steady rotation associates with a steady pitch and both in turn with the dynamics of a safe and predictable universe.

Rotational mechanical instruments are at the heart of modern musical acoustics and tone synthesis which originated with the generation of Helmholtz in the nineteenth century. Researches into the nature of tone employed a battery of mechanical resonators and vibrating devices including the siren which was later adopted by Varèse as a lead instrument in works such as Hyperprism and Ionisation. The siren resembles a bull-roarer and a piston engine in that it generates a musical sound of variable pitch related to the speed of manual rotation. A synthesis technique modeled on the siren was adopted by Stockhausen to generate a range of sounds for Kontakte: these sounds too are subject to continuous modulation in pitch and time.

Stockhausen was inquiring about the possibility of having musicians fly through the air as long ago as 1953, when 'I discussed at length with my studio technicians whether it would be wise to put musicians in chairs and swing them around, for example, and many said they might object. So then we thought it would perhaps be preferable to let them play into microphones and connect the microphones to speakers and then swing the speakers around, and then they would not object, but they objected to that too. They said, oh no, you can't do that with me, I'm here, and the sound has to come from here' (1).

Later in 1959 he experimented with rotating sounds for four orchestras (the inserts in Carré) round about the same time as he was developing the first 'rotation table' to enable the manual rotation of independent layers of sound in Kontakte. At the 1970 Osaka World Fair Stockhausen realized a dream of a spherical auditorium in which by means of a manual rotating potentiometer or 'sound mill' he was able to make sounds spiral upwards and downwards. For Sirius 1975-77 a motorized rotation table capable of very high speed revolutions was employed to simulate the sound of a quartet of arriving and departing flying saucers. Again in 1982-83 the electronic music composed at IRCAM for Kathinkas Gesang als Luzifers Requiem whirls round the solo flutist in a scene reminiscent of the whirlwind that carries Dorothy from black and white Kentucky to a technicolor world of Oz and a meeting with The Wizard (whose awesome visage, by the way, bears more than a passing resemblance to the mask of Lucifer in Samstag aus LICHT).

In every case the audience is surrounded by the rotation, and the rotation process itself is associated with the idea of being transported to another world, a world of make-believe. Helikopter-Streichquartett is one more in a long line of such processes. Four helicopters, four flying saucers in Sirius, four channels in Kontakte.

Helicopters are a genial idea for a host of reasons. They come ready-made, like objects chosen by Marcel Duchamp. They are actual transportation. A musician can actually ride in such a machine. They embody another dream of the composer: for 'a cockpit ... with lots of buttons' (2). They produce a sound more powerful than any synthesizer, with a deeper bass. And they actually fly.

Rotation is one thing, the texture of helicopter sound is another. What is important in this case is a source of vibration that demonstrates an unequivocal continuum between pulsating rhythm and pulsatile sound and pitch. A helicopter produces a sound of such a wide range as to manifest both rhythm and pitch simultaneously, the engine generating the pitch component, the rotors the rhythm component, both locked together so that they rise and fall synchronously. A similar relationship obtains in Kontakte, where electronic sounds created by acceleration of patterns recorded on a loop of tape are then subject to spatial (in this instance non-synchronous) rotation by means of the rotation turntable. A distinctive feature of the rotating sounds in Kontakte is the audible 'flap' as the sound passes from one speaker to the next, which sounds very like the beat of a helicopter rotor. Naturally Stockhausen would have preferred a nice smooth rotation without any discontinuity - as for example in the original 1941 Fantasia movie 'Waltz of the flowers' sequence. For sounds to move in space realistically it is not enough to vary the output from speaker to speaker, you have to incorporate phase changes in the spectrum of sound that convey movement relative to a listener, and this is a difficult task that Stockhausen comes back to again and again.

Impulse generated sounds are not limited to mechanical devices such as sirens or rotors. The reason a siren sounds like a human voice is that the mechanism of a human voice resembles a siren: compressed air interacting with the valve process of the vocal folds to produce a train of impulses that can be varied in frequency to vary the pitch and thereby the expression of the voice. Other examples of pulsatile sound in Stockhausen include the clapping 'Klatsch-Moment' in Momente, the 'running offstage to find the clipping shears' episode in Musik im Bauch, the 'applause' temptation in Der Jahreslauf (which makes the connection between the sound of running clogs and that of people clapping), and the scene 'Luzifers Abschied' from Samstag aus LICHT where the sound of multiple running clogs is combined with rotational motion above the heads of the audience

In the case of Kontakte the flap effect from speaker to speaker is at least consistent with the impulse generated tone material. An impulse generator is a square-wave signal generator with controls for the repetition rate (periodicity) and duration of impulse that can be used not only as a source of sound in its own right but also to control the output of a continuous signal from a second source (in exactly the same way as the holes in a siren modulate the flow of air to produce a sound).

'Since F.W. Opelt's siren researches and his theory of music "founded on the rhythm of pulsed sound waves" (1852), theorists have frequently sought to clarify the relationship between quantifiable impulses and unquantifiable impulse-generated tones . . . Serial technique in its ongoing development and tendency toward free form has put this whole problem to one side and opted for a more or less independent juxtaposition of the two parameters 'pitch' and 'duration'. Whether duration is a moment in time, or time a product of duration may be a matter of fertile discussion for psychologists or philosophers but does not resolve the question over the potential for integration of the two parameters' (3).

We are now in a position to put together the formal process represented by the four helicopters and the expressive dimension represented by the four string players.

The note material on which the string quartet music is based is also a 'given' in the sense of being already prefigured in the composer's master plan or formula. In his usual fashion Stockhausen conceives the role of the performer as imitating and coloring pre-existing mechanical sound. The violin family were originally designed by the Italians as instruments of naturalistic voice-like emotion, and in assigning the glissando element of his LICHT formula to the strings the composer is making a symbolic connection between string sound and feminine emotion, in LICHT also associated with instability, weeping and wailing. It follows that the combination of imagery of departure (the helicopters taking off) together with that of weeping and wailing (tremulous glissandi sliding up and down) suggests a ceremony of valediction.

Back in 1976 in the first edition of my monograph The Works of Karlheinz Stockhausen I noted a curious resemblance between a passage in Kontakte and one in the final movement of the Bartók Second Violin Concerto. I was roundly scolded at the time for my presumption. At 21'30 [Structure XI] in Kontakte a stream of impulses centered on F above middle C gives rise to a series of layers that 'peel off' and move away in different directions in wavy motion. In the Bartók violin concerto at 'Risoluto' two measures before [167] a tremolando solo violin starting on exactly the same pitch begins to undulate up and down in an analogous manner. (The entire last movement is a fascinating exercise in glissandos, by the way.

Just an idea. But a violin. Tremolando. Associating in my mind with impulse-generated electronic sound. Electronic sound that also rotates around the audience and sounds like a helicopter. You get my drift.

by Kontakte, it resembles Kontakte in so close a way as to demonstrate exactly the kind of tone and effect the string players need to aim for. When certain segments of the electronic work are compared to the string playing in Helikopter-Streichquartett, it is possible to imagine that the Arditti Quartet might well have been more comfortable in their task and employed a greater range of expression had they imitated the electronic sounds of Kontakte by way of preparation.

Let's start with perhaps the most talked-about segment in Kontakte, Structure X at 17'05. It begins with a powerful machine-like descending undulation accompanied by a lighter decelerating process that eventually settles on E below middle C. I am reminded of those decelerating tones when I hear the cello's gradually accelerating first entry in Helikopter-Streichquartett, and if I am not mistaken the initially abrasive attack of the cello is very quickly 'rounded off' by the composer at his ProTools monitor to give the repetition a cleaner sound. Returning to Kontakte, Structure X continues with a series of sustained low pulsating tones, broken occasionally by rasping and metallic textures. These are the most powerful tones in the entire piece.

Frictional tremolo sounds occur only from time to time. I have already mentioned the 'layers peeling off' at XI, which is analogous in terms of the idea of multiple sources coming together and moving apart against a constant background drone of impulses. There the suggestion of string tone is more marked. Most striking of all however is the final sequence from Structure XIV (31'06) to the end. Although focused way up in the high treble, the texture of sound and interaction of partial sounds seems exactly to correspond with the ensemble effect Stockhausen has in mind for Helikopter-Streich-quartett, albeit accelerated in pitch. The entire segment is frictional and rotational in character and also ventures into new territory of constant glissandi up and down, in a way prefiguring the later work (not to mention echoing the Bartók previously mentioned). This final section has been characterized (4) as expressing a sense of direction, of finality even, in apparent contradiction to the Zen-like principle of moment-form that the music goes on for ever. Stockhausen has acknowledged this could be the case. Certainly there is a much stronger emotional pull to the music at this stage, a powerful sense of brooding melancholy, of loss, of weeping.

In his notes to the Montaigne-Audivis cd Stockhausen alludes three times to an added segment of three minutes:

'After the world premiere, I added a circa 3-minute, synchronous formation to the end of the work before descent and landing.'

'After the world premiere, the musicians of the Arditti Quartet wanted to make a studio recording of the work ... including bars 64-79 (circa 3 minutes), which had been composed after the world premiere.'

'Until the world premiere, the measured music of the score (starting at bar [1]) lasted 18 &Mac184; minutes. Due to a later addition, it now lasts circa 21 &Mac184; minutes.'

Note that he doesn't say exactly where the new material begins, which is passing strange for a person of such a meticulous disposition.

At 26 minutes 52 seconds reading by the counter on my cd player this 'Schluss-Choral' begins. It is the best segment in the whole recording, a controlled deceleration in which the four voices combine in what sounds suspiciously like a textbook harmonic progression. It's unexpected and very emotional, and it also seems richer and more colorful in tone and texture than before, and it ends at 30 minutes 40 seconds. Somewhere in those four minutes I guess is the new material. Perhaps all of it is new. Like the ending segment of Kontakte it is music that has been specially composed and inserted to impart a sense of closure.

(1) Stockhausen on Music, Marion Boyars Publishers, London, 1989, 101.
(2) Stockhausen on Music, 132-4.
(3) Herbert Eimert and Hans Ulrich Humpert, Das Lexikon der elektronischen musik, Bosse, Regensburg, 1973. (translated by the author)
(4) Seppo Heikinheimo, The Electronic music of Karlheinz Stockhausen: Studies on the esthetical and formal problems of its first phase. Acta Musicologica Fennica 6, Helsinki, 1972, 206-07.

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