Scambi is Pousseur's second electronic-music work, following Seismogramme I–II (Seismograms I–II)—one of the seven works which had been presented in October 1954 on the first concert of full-scale compositions produced in the Electronic-Music Studio of the NWDR. Pousseur at this time had obligations as a schoolteacher in Malmedy and so could only come intermittently to work in the Cologne studio, where his friend Karlheinz Stockhausen helped carry out the technical realisation (Grant 2001, 75; Morawska-Büngeler 1988, 15, 109). His work on Scambi by contrast brought him into direct contact with the work of actually realising electronic music.
In the summer of 1956, at the Darmstädter Ferienkurse, Pousseur met Luciano Berio, who invited him to come to Milan to work at the Studio di fonologia musicale of Radio Milan. On his way to Milan on the train in the spring of 1957, Pousseur formulated two goals for his new work. First, he wanted to design the work in a way that permitted the listener to participate in its temporal formation, which meant it would be composed of a number of small elements which could be arranged in different ways. Second, it seemed necessary at that time to use material that avoided the periodic character of traditional music, including the internal structure of the sounds themselves. This meant starting from noise—white noise—and filtering it to produce a range of noisy sounds with different degrees of relative pitch. This came as an extension of the post-Webernian goal of exploring structures opposed to traditional ones, especially in the area of harmony, so that, in place of the concepts of polarity and causality of traditional musical thinking, "Es soll alles schweben" (everything should remain in suspension), as Webern put it (Pousseur 2004, 147–48; Pousseur 2005, 4).
A third factor preoccupied Pousseur: the time available to carry out the work was relatively short. Consequently, it was necessary to find relatively quick methods for the generation and formation of the material. This was an important factor in deciding on techniques that deviated from the microstructural devices accepted almost exclusively in electronic composition until the present time (Pousseur 2004, 148).
At the Studio di fonologia, Pousseur discovered a special filter designed by Dr Alfredo Lietti, the technical director of the studio. This device enabled selecting, by setting the filter's threshold, material from a complex sound phenomenon, or the opposite, progressively increasing the attenuation. In other words, various more or less dense "skimmed off" bandwidths can be isolated from the same stockpile of sounds. Studio technician Marino Zuccheri assisted Pousseur in compiling a supply of suitable sounds for his composition (Pousseur 2004, 147, 150–51).
The starting-point for Scambi is a collection of sound material that is globally statistical. By means of devices that enable transformation techniques, elements are selected from electronically generated white noise. Various frequency bands were isolated, each with a bandwidth of half an octave, and from each of these a sequence is filtered using an amplitude selector. The output is randomly determined by whichever sounds happen to emerge above the filter’s threshold. These sequences, which already fluctuate in frequency around average values, are then made to centre on nine different pitch levels. On each one, a directed motion of change in density is imposed in which the direction is not linear, but rather travels in a spiral fashion. An acceleration machine is then used to give each sequence a rising or falling pitch tendency, within which the motion is not even, but is disturbed by small internal deviations in contrary directions. This material is then reduced to four basic structural types, each characterised by a double tendency: on the one hand, movement from high to low or from low to high, and on the other from fast to slow, or from slow to fast (Sabbe 1977, 172–73).
Rhythms, too, are intentionally irregular and unpredictable. Details of the music are therefore "imprecise". On the whole, only general motions are heard—general speeds or changes of speeds—with abrupt breaks occurring even within these tendencies (Wilkinson 1958, 45).
A second structural level opposes this essentially discontinuous material with contrasting, long-sustained, continuous sounds, again in four types of shape. These two four-fold classes of structures are blended in various degrees to produce sixteen intermodulated structural types. Together with their retrogrades, a total of thirty-two sequences are generated: high-fast-discontinuous changing to high-slow-continuous, low-slow-discontinuous changing to low-fast-continuous, high -fast discontinuous changing to high-slow-discontinuous, and so on (Sabbe 1977, 173–74).
Once having produced these thirty-two sequences, Pousseur regarded the work as complete, though with an enormous number of possible realisations—an aleatory principle which had been intended from the outset (Pousseur 2004, 157).
Scambi is unusual for an electronic work in having a mobile structure. It consists of sixteen pairs of segments (called "layers" by Pousseur) that may be assembled in many different ways. Pousseur's original idea was to supply these layers on separate reels of tape, so that the listener could assemble his own version. When first created, several different versions were realized, two by Luciano Berio, one by Marc Wilkinson, and two by the composer himself—a longer one of about six-and-a-half minutes and a shorter one lasting just over four minutes. One of Berio's versions is shorter still at 3:25 (Pousseur 2005, 1; Sabbe 1977, 175n86). Pousseur established two principles for linking the segments together. The first is that there should be as complete a conformity in character as possible between the end of one segment and the beginning of the next, with the objective of accomplishing transitions as imperceptible as possible. The second is that the formal course should be marked by the successive dominance of the different characters. The process of assembly was complicated by the fact that the sequences were not all the same length, but it was not required that all thirty-two segments necessarily appear in all versions. Though Pousseur followed these rules himself, he regarded them only as suggestions, and Berio and Wilkinson did not conform to them when making their versions. Berio's structures, for example, are marked by an even distribution of the various characters, while Wilkinson's connections emphasize effects of contrast (Pousseur 2004, 157–58; Pousseur 2005, 18; Sabbe 1977, 175).
Initially, Scambi was not met with universal acclaim, even within Pousseur's immediate circle of colleagues. Pierre Boulez attended a concert of electronic music from Milan, given at Darmstadt on 26 July 1957, in which two versions of Scambi were presented, along with Mutazione and Perspectives by Luciano Berio and Notturno by Bruno Maderna. In a letter to his friend Stockhausen, Boulez reported:
I also heard the electronic pieces from Milan. What a catastrophe. The one by Pousseur is absolutely zero, both in the choice of material and in its compositional structure. And then, the white noise at a high level and with glissandos, which might be used for sound effects of storms... and these sorts of vaguely aquatic gurglings, and worse (just like a toilet), I find it abominable! (Boulez 2001, 180)
In his influential early book Opera aperta, Umberto Eco, on the other hand, cites Scambi, together with Stockhausen's Klavierstück XI, Berio's Sequenza I, and Boulez's Third Piano Sonata, as musical exemplars of the "open work", alongside the literary models of Verlaine's Art Poétique, Kafka's The Trial and The Castle, and James Joyce's Ulysses and Finnegans Wake (Eco 1987, 1–2, 8–10). For Eco, Scambi represents a "fresh advance" by pointing within the category of "open" works to a narrower category of "works in movement" consisting of "unplanned or physically incomplete structural units", related to products of visual art like Alexander Calder's mobiles and Mallarmé's Livre (Eco 1987, 12–13). It is evident from the vocabulary used by Eco that it is Pousseur's work that had the greatest impact on his thinking (Grant 2001, 177). Scambi was the first open-form work of electronic music—a mobile of electronic sounds (Volborth-Danys and Pousseur 1989, 42).
Beginning in 2004, the Scambi Project, directed by John Dack at the Lansdown Centre for Electronic Arts at Middlesex University, has focussed on this work and its multiple possibilities for realization.
- Panorama des musiques expérimentales. Works by Luciano Berio, Bruno Maderna, Iannis Xenakis, Jean Baronnet, François Dufrêne, Herbert Eimert, Pierre Henry, György Ligeti, Luc Ferrari, Mauricio Kagel, André Boucourechliev, and Henri Pousseur. LP recording, 2 discs: 33⅓ rpm, stereo, 12 in. Philips A 00565 L and A 00566 L. Amsterdam, Philips, 1966. Reissued as Panorama of Experimental Music. Mercury SR-2-9123 (set); SR 90478—SR 90479; [United States]: Mercury, 1968. [Pousseur's long version (6:22) of Scambi]. Second disc (including Scambi) reissued separately as Panorama electronique / Electronic Experimental Music. LP recording 1 sound disc: analog, 33⅓ rpm, stereo, 12 in. Limelight LS-86048. [S.l.]: Limelight, n.d.
- Acousmatrix—History of Electronic Music 4: Henri Pousseur: Scambi [Pousseur's long version (6:27)]; Trois visages de Liège ; Paraboles-mix. CD recording, 1 sound disc: digital, 4¾ in. BV Haast Records CD 9010. Also issued as part of the 9-CD boxed set, Acousmatrix: The History of Electronic Music. BV Haast 0206. Amsterdam: BV Haast Records, 1996. Reissued 2006. Same version of Scambi reissued with other material on An Anthology of Noise and Electronic Music. Volume #1. With music by Luigi Russolo; Tony Conrad; John Cale; Otomo Yoshihide; Martin Tetréault; Antonio Russolo; Walter Ruttmann; Pierre Schaeffer; Gordon Mumma; Angus MacLise; Philip Jeck; Konrad Boehmer; Nam June Paik; John Cage; Edgard Varèse; Iannis Xenakis; Paul D. Miller; Pauline Oliveros; Ryoji Ikeda. CD recording, 2 sound discs: digital ; 4 3/4 in. Sub Rosa SR190; Sub Rosa EFA 27682-2. Brussels: Sub Rosa, 2002.
- Forbidden Planets: Music from the Pioneers of Electronic Sound. [Unknown version of Scambi, probably the same as on Acousmatrix 4]. With music by Robert Beyer, Louis and Bebe Barron, Miklós Rózsa, Pierre Schaeffer, Bernard Herrmann, Herbert Eimert, John Cage, Karlheinz Stockhausen, Paul Gredinger, Hermann Heiss, Iannis Xenakis, Dick Raaijmakers, Tom Dissevelt, Edgard Varèse, György Ligeti, and Henk Badings. CD recording, 2 sound discs: digital, 4¾ in. Chrome Dreams CDCD5033. New Malden, Surrey, UK, 2009.
- Boulez, Pierre. 2001. Letter to Karlheinz Stockhausen, dated 25 September 1957. In Karlheinz Stockhausen bei den Internationalen Ferienkursen für Neue Musik in Darmstadt 1951–1996: Dokumente und Briefe, edited by Imke Misch and Markus Bandur, 179–81. Kürten: Stockhausen-Verlag. ISBN 3-00-007290-X.
- Dack, John. 2009. "The Electroacoustic Music of Henri Pousseur and the 'Open' Form". In The Modernist Legacy: Essays on New Music, edited by Björn Heile, 177–89. Farnham: Ashgate. ISBN 978-0-7546-6260-0.
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- Doati, Roberto. 1992. "Il caso filtrato: Scambi di Henri Pousseur". I quaderni della Civica Scuola di Musica: 21–22.
- Eco, Umberto. The Open Work, translated by Anna Cancogni, with an introduction by David Robey. Cambridge: Harvard University Press. ISBN 0-674-63975-8 (cloth); ISBN 0-674-63976-6 (pbk).
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- Morawska-Büngeler, Marietta. 1988. Schwingende Elektronen. Eine Dokumentation über das Studio für Elektronische Musik des Westdeutschen Rundfunks in Köln 1951–1986. Cologne-Rodenkirchen: P. J. Tonger. ISBN 3-920950-06-2.
- Pousseur, Henri. 1959. "Scambi". Gravesaner Blätter 4:36–47 (German), 48–54 (English). Italian translation in La musica elettronica: Testi scelti e commentati da Henri Pousseur, 135–47. Milan: Feltrinelli, 1972, French version, as "Scambi—description d’un travail (1959)". In Pousseur, Ecrits théoriques, 1954–1967, edited by Pascal Decroupet, 147–59. Collection musique, musicologie. Sprimont: Editions Pierre Mardaga, 2004. ISBN 978-2-87009-865-3.
- Pousseur, Henri. 2002. "Die Zeit der Parabeln (1972/73): Beschreibung einer Arbeit im Studio für Elektronische Musik des WDR Köln (1972)", translated by Hélèna Bernatchez. In Komposition und Musikwissenschaft im Dialog II (1999): Henri Pousseur: Parabeln und Spiralen: zwei Hauptaspekte eines Lebenswerkes, edited by Imke Misch and Christoph von Blumröder, 70–92. Signale aus Köln. Münster: Lit-Verlag. ISBN 978-3-8258-6580-1
- Pousseur, Henri. 2004. Série et harmonie généralisées: une théorie de la composition musicale: Ecrits, 1968–1998, edited by Pascal Decroupet. Collection Musique, musicologie. Wavre: Editions Mardaga, 2004. ISBN 978-2-8047- 0013-3.
- Pousseur, Henri. 2005. A Keynote Lecture. Presented as part of the Symposium on Open Works at Goldsmiths College, London, 18 February, a part of the Scambi Project, funded by the Arts and Humanities Research Council (accessed 11 November 2014).
- Smith Brindle, Reginald. 1958. "Reports from Abroad: Italy: The R.A.I. Studio di Fonologia Musicale at Milan". The Musical Times 99, no. 1380 (February): 98.}}
- Sabbe, Herman. 1977. Het muzikale serialisme als techniek en als denkmethode: Een onderzoek naar de logische en historische samenhang van de onderscheiden toepassingen van het seriërend beginsel in de muziek van de periode 1950–1975. Ghent: Rijksuniversiteit te Gent.
- Volborth-Danys, Diana von, and Henri Pousseur. 1989. "Interview d'Henri Pousseur". Revue belge de Musicologie / Belgisch Tijdschrift voor Muziekwetenschap 43:39–47.
- Wilkinson, Marc. 1958. "Two Months in the Studio di Fonologia". The Score, no. 22 (February): 41–48.
- Pousseur, Henri, Christoph von Blumröder, Thomas Böhm, and Flo Menezes. 2008. "Hommage an Henri Poussuer zum 75. Geburtstag: ein Gespräch zum Thema 'Lektüren' mit Scambi und Trois visages de Liège". In Komposition und Musikwissenschaft im Dialog VI (2004–2006) , edited by Marcus Erbe and Christoph von Blumröder, 101–15. Signale aus Köln 12. Vienna: Verlag der Apfel. ISBN 978-3-85450-412-2.