Composing With Real Time Granular Sound

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    Composing with Real-Time Granular Sound

    Barry Truax

    Perspectives of New Music, Vol. 28, No. 2. (Summer, 1990), pp. 120-134.

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    Perspectives of New M usicVol. 28 n. 2 1990)

    Please note: The original version o f this articlewa s accompanied by an audio supplementthat is not available through JS TOR at this time .For assistance in locating the supplementyou may wish to contact your librarian.

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    COMPOSINGITHREAL-TIMEGR NUL ROUND

    DESPITE THE M NY CH NGES which th e introduction of the computerinto the compositional process has brought about, it is remarkablehow frequently the compositional models implemented in both softwareand hardware retain the concepts and techniques of instrumental music.Perhaps these are the only ones which are familiar enough to computermusic system designers, or expressed systematically enough to be repli-cated. I n market-driven p roducts, the instrumen tal music model is the on lyone considered viable e nou gh com mercially.Central t o th e instrumental-music approach, and coincidentally to mostcom puter music systems, is the separation of soun d and stru cture. W ithinthe MUSIC V system a nd its many relatives, this separation is expressed asthe score and orchestra ; within the M ID I world it is imbed ded in the

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    Real time Granular Sound

    dfference between the note on , note o f f ' data and the frequently arbi-trary nature of the timbres used in th e synthesizer. A second tenet of theinstrumental approach, namely constant timbre per voice, is frequentlyenforced within these same synthesizers. Of course, the thoughtful com-poser wdl no t be misled by mere nomenclature and the resourceful experi-menter wdl always find a way to overcome limitations, i.e. the influencemay be much sub tler. But these excep tions still prove the rule. The refinedtimbral designs of Jean-Claude hsset break free from the instrumentalmusic world within the MUSIC V language; it wdl be interesting to seewhere th e M ID I world wdl find its exception.Several alternative approaches exist that un ite sou nd and structure, theones interesting me the most being those that stem from the practice ofelectroacoustic music. W alter Branchi (1983) has described the d fk re nce asthat between composing with sound , as practiced in the instrumentalapproach, and composing through sou nd . Th e acousmatic approach,usually associated with the Groupe de Recherches Musicales, provides aparticularly rich background of sonic-based thought. Among English-speaking composers, Denis Smalley (1986) has developed the acousmaticapproach the farthest with his c'spectro-morpholog~al concepts. Com-posers worlung with linguistic or environm ental materials are usually lesslikely to detach so un d from structure and m eaning, playing instead on theinterplay of these aspects. Simon Emmerson (1986) has provided an o ri g -nal insight to the classification of such approaches by his matrix of soundmaterials and sou nd syntax, each axis ra ngng from mimetic t o abstract.Over the past fifteen years of my compositional experience which hascentered on computer-assisted composition and electroacoustic studiopractice, I have sought a variety of ways of relating sound and structureintimately. A software-based compositional system, named POD (Truax1977) and later PODX (Truax 1985 ), has provided the m eans, in additionto analog s t u d o practice.Early approaches within PO D involved the m apping of timbral soundobjects on to a syntactic field. Techniques such as the tendency mask(Example 1) allowed timbres t o be introduced and gradually transformedinto variants or abruptly changed to contrasting famihes, as in onic Landscape No (1975, rev. 1977). Later work (Truax 1978) took an approachcalled polyphonic timbral construction to con struct complex timbresfrom simple frequency modulation (FM ) sources, as in my work Androgyny(1978). The next s tep involved treating timbre at a form-determining level(Example 2), as in A m 1980), where spectral families implicit in the FMmodel were used to construct the form of the entire piece (Truax 1982).Mapping timbre onto spatial patterns called trajectories was a further stepin W m e w e 1983). These approaches culminated in S o b Ellipse (1984-85), where a spinning trajectory pattern informed everything in th e workfrom the smallest base unit (one-quarter second) to the largest cyclic

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    Perspectives of New MUSI

    1

    16-20( E N V 4)

    11-15(ENV.

    0c 6-10 ( E N V 2 )1-5

    ( E N V 5)50 60 70 80 Time-90

    EXAMPLE 1: TENDENCY MASKS USED TO DEFINE TIMBRE SELECTION (TOP),FREQUENCY RANGE (MIDDLE),

    AND TEMPORAL DENSITY (BOTTOM)AS USED IN THE PO ^ PROGRAM

    pattern of the eleven-minute piece (Truax 1986a). Complementary timbralfamilies, both vocal and noise-like, articulated these processes and wereintimately entwined with them. It is perhaps significant that as theseapproaches brought sound and structure closer together, greater emphasiswas placed on both the macro and micro levels of the composition-asimultaneous process of moving inwards as well as outwards.An abrupt break in synthesis technique, though not in conceptualapproach, has occurred in my work over the past three years with thedevelopment and use of granular synthesis. This technique has been pro-posed (Xenakis 1971; Roads 1978, 1988) as a unique method of achievingcomplex sounds by the generation of high densities of small "grains" onthe order of magnitude of 10-20 ms duration. My recent work (Truax1986b, 1988) has shown that this technique may be implemented in real

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    Real time Granular Sound

    EXAMPLE 2: STRUCTURE OF OVERLAPPING AMPLITUDE ENVELOPES AwasB SED ON THREE FUNDAMENTAL F R E Q U E N C I E S ~ ~ , ~ ~ ,ND^^

    THI S U NI T STRUCTURE IN TUR N OVERLAPS WI TH ITS SUCCESSORDASHED LINES) AFTER TWENTY-FIVE SECONDS

    time using the microprogrammable DMX-1000 Digital Signal ProcessorWdraf f 1979 , thus taking the burden of data specification, storage andcalculation off bo th the user an d the machine. Synthesis techniques involv-ing additive synthesis and simple FM pairs for each grain have been imple-me nted, as well as the granulation o f stored sampled sou nd Truax 1987).hierarchy of control parameters direct the density, frequency range, andtemporal evolution of the synthesized sou nd textures.The basis of granular synthesis in the seemingly trivial grain has had apowerful effect o n my way o f thinking ab ou t sou nd . I t clearly juxtaposesthe micro a nd mac ro levels, as th e richness of th e latter lies in stark contrastt o t he insignificance of the fbrmer. Moreover, the range of densities obtain-able, from the low levels associated with human gestures through thoseperceived as rapid and virtuosic, culminating with entirely fused textures,suggests a scale of composition ranging from human proportions toabstract. Finally, in terms of the theme of sound and structure, it is clearthat t he tw o are inseparable with this technique. T he macro level structur eis best described in term s of its com pon ent sounds, and t he resulting s ou ndcomplex is definable only in terms of th e struc tural levels tha t characterizeits organization.

    To date, I have composed fou r works with the granular synthesis techn ique.Th e first, iverrun 1986), is based on synthesized grains which are either

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    Perspecttves of New usic

    simple waveforms or FM signals. However, despite the basis in fixedwavetables, the resulting textures are always dynamically changing andrange from swarms of relatively isolated s ou nd events to fused so un d massesof great internal complexity, m uch like environm ental sou nd generally an dwater so un d in particular. T h e fundam ental paradox of granular synthesis-that the enormously rich and powerful textures it produces result f