04 Pressnitzer Daniel & McAdams, Stephen - Acoustics, Psycho Acoustics and Spectral Music

8/3/2019 04 Pressnitzer Daniel & McAdams, Stephen - Acoustics, Psycho Acoustics and Spectral Music

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intuition consisted infounding compositional systems on the structure ofsound, and thus in deriving fields of musical relations from Bound itself."Thewager of such an approach is to give to a listener reference pointsthat are naturally understandable, while allowing the use of the newpotentialoffered by micro-compositional work at the level of sound. In.other words, the structures sought should be latently intelligible, sincethe elements necessary for their comprehension are contained in thematerials. T f the work of the forerunners of this approach was foundedonly on intuition and experimentation, the will togo further, to not letoneself be enclosed by a limited number of effects or gestures, requires amore rigorous conceptualization and formalization of the fundamentalideals. A perfect understanding of acoustic phenomena is th us necessaryand we will address this domain. by insisting on the importance of differ-ent representations of sound. Though it is necessary, this comprehensionis not sufficienf: what counts in the end is certainly (at least in the logic ofthe spectral approach) what is perceived and understood by the listener.It is at this level that p ychoacoustics, which extends and validates thereflection on purely physical tructures, enters the picture.As uch, it is not by a will to 'scientism' at any co t that the 'spectralcomposers were undoubtedly drawn to interest themselves in these dis-ciplines, but simply because of a necessity that proceeds from theirapproach. Numerous questions thus naturally come to the fore: What infact is 1 1 sound? What are its possible representations? What are the inter-pretations made by perception to extract from a sound what is relevantfo:r the listener? Can we exploit them musically? Can we speak of 'soundobjects' in om psyohological representations? How do we think music?Doubts can also appear, notably with respect to a fundamental aspect ofmusic: if tonal harmony is considered as a sort of syntax, allowingexpression by changes in tension that occur as one deviates irom certainrules, it relies undoubtedly n a trang, e v e n implicit, cultural learning.Is it possible, inno longer using this solid, conventional prop, to find abasis contained in the material of sound,lor the expression of tension? 111an attempt to respond to these questions, and especially to incite newones, we will. present a set of facts concerning sound and its perception,starting with .itsbirth in the acoustic world.

The acoustic worldRepresentationsA vibrating body creates in the surroundingairthe propagation of apressure wave, in the same manner that the agitation of all. object on a


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surface or water provokes the propagation Ofwavelets, This is the physi-cal reality of sound, thevariation of acoustic pressure over time, and thisreality is unique. It can, nevertheless; be represented in different waysaccording to the infortnation that Onewishesto emphasize. Take theexample of a chord from the pieces Streamlines by Joshua Pineberg (1995).Its classic musical representation is the score' (Fig. 1). Centuries of expe-rience allow the use of this symbolic representation for compositionalptuposes, but in fact it constitutes more a set o f instructions to the per-formers than a deseriptionef the sound actually produced. For example,if the instrumentation changes, {he music transcribed in t.he score istransformed, In Baroque music, where exact instrumentation was oftennot specified, and in .some pieces of contemporary music, where theinstrumentation is,specified vaguely as in the percussion piece }onisatiol1.by Edgard Vares (1933), the sound structure itselilll2lY be completelydif-ferent from one rendering to the next.To obtain a trace of a specific sound, it is possible to c.apture it througha recording device that will convert the pressure variations into some-thing that can be visualized (Fig. 2). This representation of the pressurewave reflects all of the fine-grained temporalevolution (within the reso-lution limits of the visual representation). It is therefore particularly well-adapted to marupulations of sound such ascutting and splicing, reversal'l , Classic up to a certain polnt, considering the presence here of quarter-tones!


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in time or repetition, In its eqrly daY$, mueiq ue cl:m crel.:e, because of theavailable technology, worked with razor blades on tapes containing theexact magnetic retranscription of this temporal wa.ve and thus used a lotof these. kinds of transformalions.2. However, this temporal image doesnot translate inan obvious fashion the different pitches that it is possibleto dtstingulsh in listening attentively to such a chord,A representation that allows this i f ; > the one based on Pourier 's theory.

TIUs theQl'Y states that any complex signal can be decomposed into a SU:Q1of sinusoidal wave-s, over. an infinite time frame, by specifying preciselytheir relative amplitudes and phases. It is thus possible to decompose acomplex sound into a sum of sine tones, which are called the partials ofthe sound, the set of which form its spectrum (Fig. 3). This Fourier trans-form represents well the same chord, but in a different form, unveilingits frequency conteJ_1t , This knowledge of frequency components presentin the sound, which, may 'under certain conditions be heard as '.spectral

2 ., One should note in passing the influence of the tools.used on theend result


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pitches' (Terhardt, 1974), is at the origin of 'the emblematic idea of themusic that is, appropriately, called 'spectral'. As an example amongothers, Jonathan Harvey's piece Mor tuo s phmgo , V I.1 JOS V06 :0 (1980) uses thespectrum of a ben sound and its transformations as a foundation for theharmony. If such a representation is a source of fertile inspiration, itmakes the temporal information about the sound no longer explicit inthe transform as the analysis is (theoretically) over an infinite duration.The true natura o r a sound phenomenon as we perceive it is double: itevolves over time, which is represented by the temporal wave, and italso has a certain frequency content, VIsible in the spectrum. The short-term. Fourier transform reconciles these two types of Informations. It isthus called a 'time-frequency .represenration', The sound is sliced up, byan analysis time window, into successive instants. The Fourier transformis thencomputed for successive instants by sliding the window OVer thetemporal waveform bit by bit. In this way the evolution of the frequencycontent of the sound is represented over time, the result 0'[ tilis analysiscan be presented either in the form of a spectrogram (Fig. 4), havinggraphical similarities to a musical score, or in the form of a three-dimensional perspective plot thatexpresses the acoustic variations in


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terms of frequency, amplitude, and time.' This type of analysis is essentialfor performing additive synthesis, or its orchestral derivations. In Partiel(1975), for example, Gerard Crisey explores the sound of a trombone byassigning to different instruments the production of agiven partied of thetrombone spectrum analyzed with its dynamic temporal evolution. Therepresentation asa short-term Fourier transform is quite general, but itshould be noted that there is an inevitable compromise between thetemporal resolution (the duration analyzed) and the frequency resolution(the analysis precision). For a high frequency precision, a long analysisduration is needed, and so there-is a loss of temporal precision.There are other representations that allow an optimization of this com-promise (Loughlin, Atlas, and Pitton, 1993), some, such as the wavelettransform, adapting it to the frequencies analyzed (Combes, Grossman,and Thamitchian, 1989).This produces for a given sound various eCluiva.lent representations.The idea of continuumIn th physical world, frequency, time, and intensity are considered ascontinuous dimensions. Music, on the other hand, has been built on dis-crete scales of pitch and duration made necessary, among many otherreasons, by the desire to notate events and by instrumental playing con-straints. The different representations, we just presented, associated withsound synthesis, give us access to the physical continua. This allows us,as Varese noted, to catch a glimpse of an alternative to the 'fil a couperl'octave'." From this point onward, between each degree of the scalethere Can be a continuous thus infinite world to be discovered and orga-nized.Another continuum is revealed by these mathematical representation.What difference is there between the spectrum ofa note associated witha timbre and the spectrum of a chord considered as an element ofharmony? The answer is to be found on the computer screen: at firstsight, there isn't any! A simple note is a collection of spectral compo-nents, thus a. chord; and a chord is a collection of partials, thus a timbre.Sound synthesis allows. the organization of the note itself,.i:ntr.oductngharmony into timbre, and reciprocally sound analysi can introducetimbre as a generator of harmony, This ambiguity is strikingly demon-strated in Iean-Claude Risset's piece Muta t ions (1969), where the same

3. It should be noted that it is possibl to obtain spectrograms inan ana logous fashion witha bank of filters. From a theoretical point of view, the two descriptions of the short-termtransform (running window and filter bank) are equivalent (Allen and Rabiner, 1977).4. Literally ,i 'slicing up of the octave', i.e. the equal-tempered scale,


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material is treated alternately asa harmonic chord or a gong-like timbre.If harmony and timbre are sointimately linked, the clear-cut traditionalclassification of chords between perfect consonances, imperfect conso-nances and dissonances mCily become irrelevant. Timbre manipulationopens upl:he possibility to look for a continuous scale that couldrepro-

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duce, in some respects, the expressive means associated with the tonalnotions of consonance and dissonauce'The exploration of such a dimension has been undertaken by manycomposers, essentially in an intuitive fashion. Tristan Murau, forexample, has ordered timbres and aggregate with a measure of in-harmonlcity (Disintegrations, 1982)_ Kaija Saariaho has defined asoundz'noise axis intended to reproduce the harmonic capacity to createtension and relaxation (Verblendtmgen, 1982-84). Joshua Fineberg hasadopted a hierarchy founded OIl the pitch of virtual fundamentals(Streamlines, 1995). Is it possible that a single phenomenon is hiddenbehind these different intuitive criteria? Hermann von Helmholtz pro-posed an axis of reflection in drawing our attention to the attribut ofsou.nd that he called 'roughness' (von Helmholtz, 1877). Two pure tonesproduced simultaneously and having closely related frequencies createamplitude fluctuations in the waveform that are called 'beat' (Fig. 5).These fluctuations, according to their rate of beating! can give rise to agrainy quality in the sound. An example of this rough quality can beheard, emerging from silence, at the beginning of rO~Iir , Centre-jour(Grisey, 1980). Helmholtz thought he saw in roughness the acoustic basisfor the dissonance of musical intervals. Western music employs princi-pally instruments with harmonic spectra. The partials of their complexspectra are superimposed. when an interval is played, resulting in beats iftheir frequencies do not coincide perfectly. Intervals With simple fre-quency ratios, such as the octave or the fifth, do have a significant degreeof harmonic coincidence and thus less beating. However, intervals suchas the tritons create a situation where harmonics of one note beat withthose of the other note (Fig. 6). Coming back to the previous examples,an inharrnonic sound can be a source of roughness when superimposedon harmonic sounds; sounds described as noisy can often he rough; asound with a very low fundamental frequency has partials that are quiteclose to one another which creat s beating. As such, it may be that thesame acoustic feature guided the cornp0sers mentioned above ill theelaboration 01 their 'hatI 'Ll,oJ:l ic' criteria, J this was. to be the case, such afeature could be used to define a new continuum related to the vast andcomplex notion of musical dissonance, as some kind o f an 'acousticnucleus' forit (Mathews and Pierce, 1980).One might be overwhelmed before the immense field of possibilitiesthat is thus opened. The mass of data available to the composer that arederived from progressively more precise and sophisticated acoustic5. In the Western. early polyphoni period, the scale of consonance and dissonance con-tained up to six different degrees. The later simplification. of this seals an be paralleledwith the progressive affirmation uf syntactic tonal rules (Tenney, 1988).


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cared in the inner ear to the ba ilar membrane, and the waves propagateand are damped along this membrane. The stiffness of the membranevarie along its length. Due to this property the higher frequencies createa maximal displacement at its base (near the ossicles), while lower fre-guencies maximally stimulate the other (apical) end. These deformationsthen result In electrochemical changes in the hair cells that are arrangedalong the length of the membrane. These cells in turn stimulate the fibersof th auditory nerve, along which electrochemical impulses are enttoward the brain.The e ential point to understand here i that the fir t thing thathappens to an acoustic signal in the inner ear is somekind of a spectralanalysis. In fact, starting from the temporal wave, the basilar membranespatially decomposes the signal into frequency bands. The second impor-tant point is that the hair tells, in addition to codin.g the frequency posi-tion of the Signal components, also pte erve to a certain degree their


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temporal Information by produoing.neural fuingsat precise moments ofthe stimulating wave they are responding to. This phenomenon, called.phase-locking, decreases, with Increasing frequency and eventually dis-appears between about 2000 to 4000 Hz near the upper end of the rangeof musical pitch. The auditory system thus performs a double coding ofthe sound, both spectral and temporal, in such a way that all the ClUeSpresent in both kinds of representation may be available simultaneouslyin the sensory representation sent to the brain.More than just a transmissionThe coding mechanisms introduce certain phenomena that generateparadoxes and ambiguities. Sound components called difference tonesor combination tones are a first example of the necessity to become irtter-ested in perception: in addition to physical representations, TWo puretones presented simultaneously to the auditory system stimulate thebasilar membrane at positions that are associated with their respectivefrequencies. but also at positions corresponding to frequencies that are' the completion, toward lower frequencies, of the harmonic series. Thecauses and behavior of all these distortion products are not fun), under-stood. However, it is easy to hear the difference tone that corresponds tothe simple difference between the frequenciesphysically presented to theear, This tone is a n the more audible at higher levels. It has even beenused compositionally, for example, in Gy6rgy Ligeti's Ze hn S Ule ki'! JlhBli iserqui l1tet t (1968). The phenomenon can be heard at the end of the firstpiece, for instance. The difference tone belongs to the world of physiol-ogy and perception: even if it is not present in the stimulating waveform,it is created physically i _ L 1 the inner ear. It can also create auditory beats inthe same way as a 'real' sound since it is mechanically present on theba silar membrane.The frequency decomposition realized by the basilar m mbrane ismechanical: the displacements of the membrane are not Iimited tospecific points but are spread out over a portion of it. If two componentsOf a complexsignal are close In frequency, these displacement willoverlap. There is thus a minimal resolutien, called the. critical band(Greenwood, 1961), inside of which ~heear cannot separate two simulta-neous frequencies. The width of this band varies as a function of thecenter frequency considered (Fig. 8). The mechanisms underlying thecritical band play all essential role: two components will not at all havethe same. perceptual effect if they ate resolved, thus heard separately, otif they fall within a single critical band, Let us ju t make clear that thewidth of the critical band does not at all repre ent a frequency bandwi thin which all sounds are perceived to have the Same pi tch, Due to the


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temporal coding, the ear is sensitive to differences in frequency that areless than 1%,.The critical band is not a limit in precision, but a limit inselectivity.This selectivity limit is obvious in the masking phenomenon.Simultaneous masking is related to the overlap of excitation pa tterns onthe basilar membrane and to the amount of activity present in the audi-tory nerve that represents each sound component present. Simultaneousmasking can be conceived as a kind ofswa roping' of the neural activity

Clue toone: sound by thatof another (usually more intense) sound. Forexample, high-level components (noise, partial) create a level of activitythat overwhelms that created by lower-level components, which are sub-sequently not perceived at illat are perceived as being of lower levelthan they would if presented alone. The different components of acomplex sound can also interact, mutually masking oneanother, somehaying a sensation level that is lower than their actual pl,ysical levelwould lead one toexpect. 'Masking relations are determined largely bythe excitation pattern on the basilar membrane, This pat:texn is


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increase . Therefore, the frequency and amplitude relations betweensounds will affect their masking relations in a non-trivial way (Fig. 9).The knowledge of these relations is nevertheless essential to understandwhich part of a musical message win actually be perceived.The critical band also influences the perception of beats betw en twotones. Acoustically, the rate of the beats increase with their frequencydifference, As such, as the two pure tones are mistuned from unison, weshould hear beats that result from their interaction becoming progres-sively more rapid. Tills is; in fact what happens at the beginning of theseparation. But very soon, (after approximately 10 beats per second or a10-Hz frequency difference) our perception changes from a slow fluctu-ation in:amplitude toward an experience of more and more rapid fluctu-ations, that produce roughness. Finally; if the separation becomes largewith respect to the critical band, the strength of the sensation of beatingdiminishes, leaving us with the perception of two resolved pure tones.Three very different perceptual regions can therefore arise from the sameacousticalstimulus. Let us come back for a minute to our on-going

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roughness example. The Toughness of beating tone pairs (measuredthanks to experiments involv:ing judgments byhuman listeners) has beenfound to depend not on. the absolute frequency difference, but rather ontbe frequency differencerelated to the width of the critical band for agiv:encenter frequency (Fig. 10)..Roughness should 1101 therefore bethought of as an acoustic feature of sound, it definitely belongs to theworld of perception, This has several consequences. As thewidth of theband varies (Fig. 8), a given pitch interval won't have the same rough-ness in different registers. Thirds, for example, are free of roughness inthe upper register but can be quite rough in the lower one. To be ableto predict that, one needs some kind of model that could extract therelevant features from the acoustfcal signal and combine them.ModelingWe have seen that all we can hear ina sound is 1)0.1 obvious in any of itsphysical representations. In the case of roughness, these representationscan even be seriously misleading. Shouldn't it be possible to proposemodels that allow one to predict, on the basis of data obtained from ps)'-choacoustics, which percepts would be induced by a physical stimulus?It is necessary to take certain precautions: a classic psychoacoustic studyprecisely characterizes a particular phenomenon by creating artificialstimuli and byanalyzing thejudgements of listeners within acontrolsdlaboratory situation. Quantitative data are thus. carefully obtained foxeach of the phenomena mentioned above and for ITl.ahY others as well.


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The relations obtained call serve as the basis for models, but in generaleach :model describes a particular mechanism within the constraintswejust mentioned .. In using these models for musical purposes, it is neces-sary to take into account a large number of phenomena, which of courseinteract ina complex way.1tis extremely complicated, not to sayimpos-sible, to establish a coherent ensemble from a11of these sundry parts.However, some of these phenomena are beginning to be understood inphysiological terms, from which derives the-idea of modeling the causesrather than reproducing the effects .. In modeling the behavior o r thehuman ear, all of the interactionsand distortions are taken into account: in an Implicit manner (to the extent that themodel captures well theproperties of the auditory system). In such physiological models(patterson, Allerhand, and Giguere, 1995; Seneff, 1988), a newrepresenta-tion of the sound signa] is in fact proposed. This representation provides,an image of what is effectively heard, within the limits of our ability tolearn to read it. The previ.ous representations were entirely orientedtoward the mathematical description of the signal. Physiological modelsare to the contrary adapted to OUr perception, The sound synthesisprocess could be oriented by such representations, recentering the work

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on the relevant perc~ptual parameters (Cosi, De Poli, and Lauzzana,1994). The analysis can benefit as well: for example, roughness. hidden inthe other representations since it belongs intrinsically to the world ofsensation, i.shere revealed. by the fluctuationswithin each critical band(Fig. 11). These fluctuations are a reflection of the perceived grainyquality. The images produced by such models thus potentially character-ize the evoked sensations. The sensations are however only very ba iicbricks upon which the mental representation of the acoustic world thatsurrounds us is organized.

Audito,>y scene organizationAttditory representationsWhen listening to a noisy environment, or to a piece of music, Om audi-tory experience is usually quite different from the collection of inter-leaved sinusoids, with frequencies and amplitudes vary.ing over time,that nonetheless constitute the only available information that reachesthe ears. Quite to the contrary, we structure the acoustic world in termsof coherent entitie that we can generally detect, separate, localize, andidentify. For example, in a concert hall we hear separately the melodyplayed by a flute soloists, the cello ensemble, a sudden percussion entry,and our neighbour sighing -iT; certain concerts.This 'capacity is quiteimpressive, The chaotic form of the time-frequency representations of thesuperposition of all these vibrating sources, that resemble the peripheralanalysis we just described, i totally unintelligible to the human eye andeven to the most powerful computers. Audjtory organization is nonethe-less of-vital importance for the survival o f the species, if only to be ableto distinguish the flute solo from a fire c larml This importance allows usto state that a listener will always try, whatever the situation or listeningstrategy, to structure the acoustic world that confronts his or her ears.The creation of a structured representation is what allows musk to bemore than a simple succession of percepts.The metaphor of the. auditory image intuiti vely incorporates the modeof structuring that is used. An auditory image can be defined as a psy-ohologtcal representation of a sound entity that reveals a certain coher-ence 'in its acoustic behavior (McAdams, 1984). This definition is broadenough to allow it to b employed at several levels: a single percussionsound is one auditory image, the collection of events composing therapid melody played by the flute is another, all those emitted by the cellosection playing in harmony a third. From research attempting to makesense of all the possible sound cue that the brain uses to organize the


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sound world appropriately; it eems that there are two principal modesinvolved in auditory image formation: perceptual fusion of simultane-ously present acoustic components and the grouping of successiveevents into streams.Vertical organization: perceptual fusionOne of the first immediate effects of vertical organization is the groupingtogether ill a same image of the multiple partials of a complex soundspectrum, as analyzed by the ear, into coherent parts. This kind of organ-ization allows us to hear a note played by a violin as a single note ratherthan a collection of harmonic partials. The main object of vertical organ-ization is therefore at each and every instant to group what is likely tocome from the same acoustic source, and to separate it from what iscoming from different acoustic' sources. One of the characteristics ofmusic, as we shall see, is to constantly try t break. down this simple rule,However, the cue used by the auditory system to form vertical imagesremain thesame in musical and non-musical contexts. Understandingthen" is of course the key to being able to go beyond the simple equiva-lence between a vertical image and an acoustic source.The po ition of a source in space Introdu e difference between thewaves received by each ear (tim delays, intensity differences) that allowa listener to localize it. A first cue of gr01~ping is thus made available,one image for each spatial source. Localization can playa musical role, asin the religious antiphonal music of Cabrieli as early as 1600.Compositional writing for the classical orchestra, with its codified dis-position of the instruments, integrates more or le s consciously the cuesof localization in it form. It is thus undoubtedly to favor the formationof 'vertical' auditory images that some composers using tape or Liveelec-tronics music do not hesitate tospatialize their scores. Nevertheless,when one listens to sound emi-tted by a . single loudspeaker, and fhusoriginating from a single physical source, it is possible to have a m re orless dear representation of differ nb auditory images. Imagine fQJ; amoment listening to a monophonic recording of a wind quintet playedover a loudspeaker: in general you should have no trouble perceptuallysegregating the five sources. Other strategies are thus available to the ear,based on regularities in the environment that would have been learnedthrough an evolutionary process (Bregman, 1990). It is highly unlikely,for example, that different partials start and stop at exactly the same timeif they do not come from the same source. The ear tends to grouptogether partia Is that start together. If several partials evolve over time insimilar fashion (this is called the common fate regularity), they win havea high probability of coming from the same. ource: as a matter of fact, a


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modulation of the amplitude or of the fundamental frequency of a'natural ound affects all of its partials in a similar way. And finally, a har-monic series win probably come from the same sound source due. to thephysics of sound production in forced vibration systems such as bowedstrings and blown ail: columns. All these eues can be used together toform vertical images.Horizontal organizations streamsThe second level. of the auditory image metaphor enters the realm oftemporal evolution and studies the formation of auditory streams. Astream is .a sequence of events that can be considered to come from asame source. A stream constitutes a single auditory image that is distrib-uted over time. For example, the voice of someone speaking or a melodyplayed on a musical instrument possesses a certain perceptual unity andthus forms a coherent image.The general law governing the formation of streams appears to beba ed on spectral-continuity (McAdams and Bregman, 1979). This lawalso reflects . orne kind of regularity in the environment, as a soundsourc tends to change its parameters progressively over time.Conti tuity is evaluated according to s-everal cues. The m st studied oneswere frequency and time proximity (van Noorden, 1(75). E ents that areclose according to these dimensions will tend to form a separate stream,just as melodieshavlng a small range and rapid tempi in different regis-ters from one another will be segregated into different voices. Thereis atrade-off between time and frequency proximity for stream formation.Actually, most combinations of these to parameters give rise to anambiguous perception where streams can be voluntarily built ormodified. Timbral similarity is another grouping cue brought into playby orche tration.The formation of auditory stream has dramatic effects on the percep-tion of the acoustic events. judging the timing between two successiveevents is usually a trivial task, however, if the events are part of two dif-ferent streams the judgments become impossible (Bregman andCampbell, 1971). Melody reoognitionis also affected bythegrouping ofall the correct notes in a same stream (Dowling and Harwood, 1986),Emergent attributesVertical and horizontal grouping mechanisms can interact in a complexmanner, It imore than likely that at SOmemoment of an e olving audi-tory scene, energy ina certain frequency region could be attributed toseveral different verfical images, or to an ongoing stream. JJ l this case,choices are made and once this energy has be 11 attributed to an auditory


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image, it is taken away from the others ..TItis 'stealing' of energy betweenimages can lead to the consequence that attributes such as pilch andbl;ightness (Breg.man and Pinker, 197&) Q[ loudness (McAdams, BotteandDrake, in press) or roughness (Wright and Bregman, 1987) can 'be alteredby auditory organization, The expression 'sound object', if used regard-less of its.original historical context of n1uBiq1: !econcre te , can therefore bemisleading. A sound object implies a sound event possessing a basicunity, defined by some characterizable features. It is in fact the case thatall sound. properties are dependent on dynamic relahonswith thecontext, within which attributes as important as pitch, loudness, rough-ness, and other dimensions of timbre can find themselves significantlychanged as streams and vertical images are formed and reorganized.There exists no indivisible, staple sound object, but rather auditoryimages that possess more or less coherence in a dynamic relation.Each vertical auditory image, once it is. fanned and only then, pos-sesses emergent attrfbutes, These emergent attributes are born of thefusion of its eomponents, An emergent attribute is different from thesum of elementary attributes of the components contributing to theimage. The addition to spectral components higher in frequency to apure tone can lead to the perception o f a pitch lower than the originalputa tone one, as in the case of the missing fundamental (Schouten,1940; Terhardt, 1974). The recognition of a certain sound source emergesfrom the fusion of many components into a global6mbre, each of themtaken alone often being unable to unveil the sound origin (McAdamsand Bigand, 1993). Correct aJ,ldi~Qrygroupll:tg is therefore essential tobuild these emergent attributes and grasp a representation. of a naturalenvironment,Auditory imagesand musical structuresThe usual 'result o r auditory organization is to build stable auditoryimages, each. corresponding te a sound source, to he able to recognizethem. In a musical context, the emergent attributes, often COme from''Chimeric' sound sources. If each instrument of the symphonic orchestrawas tq be heard as a single source, the perce.phort of the musical struc-tures imagined by the composer would certainly be quite difficult -c-justas difficult as if all the Instruments were fused into a single auditoryimage, Auditoryorganization has therefore been explored by composersfora long time.Deceiving processes of horizontal organization allowed the writing ofvirtual or implied polyphony, wl',ere a:monopl1onicinstrume.nt-exp:ressesmore than one voice at the same time. Tricking processes of vertical organ-ization is the key to orchestration, where unheard o:fand augmented


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At' tWo/ics, Psycl'wacollslic;;Ofld Spcr:lm l M rlsic 53

timbre can be created by fusing different instruments, It can also haveradical structural consequences. In his piece Lantana (1967) , Ligeti createsdense structures within which, because of verticalfusion cues, the instru-ments cannot be distinguished. He then remarks that 'polyphony iswritten but One hears harmony'. A few years later, organization cues thatinduce the exact opposite conseg,uences were to be used by the samecomposer to write the S an F ra nc is co Polyphony (1973~74),this time clearlyheard as polyphony,TIle organization of the auditory scene can even be an argument for

musical structure. A first example of this is .Mutafions by Risset where thetransformation of a chord into timbre that we mentioned earlier is donewith. the help of auditory organiza tion cues. The inharrnonic structure ofthe chord requires the convergence of other cues such as synchrony to beheard as a fused timbre. Another even more. extreme example is the pieceDesintegNl,t ions by Tristan Murail (1982). In this work, a set of intervals isfirst heard fused ina section with a rapid tempo, comprising a complexmelodic .line, though it will be heard in a 'disintegrated' version in anearly static section. This structure is expressed by using different orga'-nizational cues (see Figs. 12, 13) ,

Figure 12


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- f _ g 1 t d t E ; l 1 : ~ ; e _ ' ; a!@" ,., r'~:;$4~~~1:=~:OifI. . . , ~ -, 'i'

I --:t:;:j~:4 ;' ,~ 'I I , - - - - = - ' j =.I1~~L j. . . .t ';: : .jg ~

I 1, I""= = r== r= -.--- _- -_

I ,

Figure 13

Listening and cognitionMemoryOf course, the bottom-up processes that we have described so far, thattook us front acoustic vibrations to auditory images, are not the onlyones to intervene in rnusicallistening, nor even in th formation of audi-tory images. A complex et of high-level cognitive pJ."Ocessesalso comeinto play. Without pretending to describe exhaustively and preciselythese processe1?(insofar as this is possible), we would like in concludingto addresscertain cognitive .aspects of listening, stressing the ones thatare associa ted more notably with ..memory,Various notions are implicated in music cognition: we mjght cite atten-tion, cultural knowledge, and temporal organization in perception. Acommon characteristic s ems to tie together these kinds of processes asthey play a role in listening: memory. Memory is Iinked to attending inthe sense that attention. seems to be predisposed to focus on events thatare expected on the basis of cultural knowledge abstracted from past,experience Oanes and Yee, 1993). Memory allows listeners to implicitly


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learn the basic rules of the musical cultl;rr to which they belong(Krumhansl, 1990; . Bigand, 1993). Finally the very notion o f time, soessential to music, derives from our ability to mentally establish eventsequences through t.heuse ef memory (Damasie et al., 1985).The auditory mod.e of recall is remarkably powerful. Crowder and

Morton (1969) have shown, ina task requiring listeners to recall a listpresented either visually or auditorially, that theauditory modality has anet advantage over the visual modality for the later elements in the list.The hypothesis advanced to explain this superiority is the existence of asensory storage: a .sort of 'echoic' memory specific te hearing, that COIl-serves the stimulus trace for a brief period of time. This hypothesis hassince been refined and there are most likely several different retentionintervals (Cowan, 1984).One of these intervals would be on the order ofseveral hundreds of milliseconds and another one on the order of severalseconds. The first storage would be related to sensation, constituting asort of 'perceptual present'iwhile the second one would serve as a basisfor what is called workingmemory, These fairly shod durations raise allkinds of questions concerning the possibility of apprehending structuresextended through time and carried by sound. The stimulus trace van-ishes within ill few milliseconds of the echoic memory, and the working:memoty cannot hold more than a few items, .Still, we can experience a perception of form and meaning over timewith spoken language, for instance, which is also carried by sound. So isthere a long term storage of the facsimile of the: acoustic stimuli wereceive? In facti there are a great deal of both behavinral and neurophysi-ological data that lead us to believe that there is not a rnemdry centerwhere this kind of storage takes plaCe in the brain (Rosenfeld, 198:8).Memory would rnore likely be distributed, as a by-product of cognitiveprocessing, in the form of p b t r u 7 t i a l repl~esentativ1' ls . In. other words, in thepresence of a stimulus, the brain activity results in the extraction o:f therelevant features, making generalizations, and. fotmin ..g categories. Thistheory has some physielogical basis . Perception activates the primarysensorycortices in the brain, which through their activity in time detectand encode different features of sound. These activity patterns are thenprojected onto association cortices. Each neuron in theassociation corticesreceives a large number of connections from various areas of the brain,whiohallows for generalization: sdmull-sharing similar features wtll actiiY~ate the Same groups of neurons, reinforcing the connections between theconcerned sensory COrtices and these neurons. When a new stimulus isperceived, if It is similar enough te a potential representation alreadytnernorized.iit will be categorized as a member of the same family. Inrecall o.r in imagination or dreaming, or also in forming ~ategories1 it


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would be the convergence zones. that then activate the sensory cortices inthe reverse direction (Damasio, 1994).The transformation of stimuli into potential representations, which arenot reproductions but rather abstractions of features of a stimulus, canhelp to interpret a study on the memory for melodies by Crowder (I993).The recall of melodies seems first of all to be based on the pitch contour,if recall follows shortly after Iearning has taken place. However, if recallis delayed in time, the influence of contour decreases to the benefit ofpitch relations: an abstraction has been performed from absolute pitch,an early level of perception, to relative pitdli.ntervaJ.\'l arid relationswithin a tonal framework. It is this. kind of abstraction that seems to bestored 'in long-term memory,This leads us back to what is implied in the possible use of differentcontinua, for only discrete scales allow a classification of perceptualvalLies that is apt to be coded inthe brain in terms of abstract relations. Infact, the existence of discrete degrees dividing the octave is one of therare constants tha t can be found throughout nearly all cultures (Dowlingand Harwood, 1986). .Fur.ther,numewus studies on musical cognitionseem to converge toward the importance of metric and rhythmic hierar-clues and thus of the discretization o f time (Lerdahl and J ackendoff, 1983;Clarke, 1987). The question is also raised 'for the use of timbre, seen as apotential carrier of structure, and its various.vapparenrly continuousdimensions (McAdams, 1989). These cenaideratiorrs on memory thushave .a direct influence on musical structures, if one WaLlIS them to heIntelligible.

ArousalAfter all these considerationsabout acoustics. psychoacoustics andcog-nition, a text about music would seem. to politely avoid an uneasy pointif it did notaddress, even superficially, the question of arousal (D remotion) in music. This issue, which may be considered at first glance tobe beyond the field of scientific irrvestlgation, -orwith one foot in the ~es"thetics domain, is in fact the subject of numerous psychological studiesthatcould find all application in the musical domain. : 5 0 , what is arousalfor the cognitive psychoJogist?An interestinganswer is proposed by Mandler (1984). Human beingshave a certain number of schemas, some innate and directly linked tosurvival, others acquired and eventually modifiable that are linked topast experience. Perceptions are thus evaluated in terms of expectancies.In the case of a perception that conforms to our expectancies, one mightexpect that little ccguitiveactivity is necessary. On the other hand, a . per-eeption that goes against expectancy triggers both an emotional reaction


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and cognitive processing, the latter in order to adapt our representationof the external world to what has been perceived. Damasio goes evenfurther, in showin,g by way of numerous examples from neuropathologythat preceding amasa! IS not only sufficient, but also absolutely neces-sary for the correct operation of many cognitive processes such associally relevant decislort-making and personal planning for the future(Damasio, 1994)..If aroused occupies such an important place in our cQg-nitive processing (usually associated with 'pure reason'), the question oftherelation between emotion and music takes on a new dimension.Let us try to make a parallel between what we learned from cognitive

psychology and what happens inmusic listening. Bregman (1 '990) clearlystates that schemas influence the way we organize the auditory scene, byproviding us witha mechanism to extract certain tbjngsth


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acculturation that we have of basic harmonic rules.P However, when thecomposer leaves the well-trodden path of convention, the mastery of acue aBowing the expression of a sin.1:ple and immediate tension canbecome primordial again, FOT example, the piece La. tempestu t / 'apri?9Giorgione by Hugues Dufourt (1977) .is constructed as a movement oflatent tension going (nearly) all the way to its Ow n paroxysm. This pieceemploys wind instrumentsin a very low register. In the Lowregisten thespaeing between the partials of the instrument sounds are very smallcompared to the critical band. Different partials thus fall into the samecritical band: this induces a pe];cepti'on of roughness. The same materialtransposed to a medium or high register would lose its meaning to alargeextent. As such, acoustics (the beats) and psychoacoustics (percep-tion of these beats) contribute to the structure of the piece! Gerard Criseycan therefore exclaim.r'we are musicians and our model is sound, notliterature, sound, not mathematics; sound, not theater, plastic arts,quantum theory; geology, astrology, oracupuncture' (Gdsey, 1984, p. 22,asquoted by Wilson, 1989). Spectral music, in its .search for expressionthrough the material itself, without hidden or conventional reference,makes possible the recourse to . certain. data Iromaeoustics and psyche-acoustics not only to justify certain choices a posteriori, but also as ameans of formalizing.musicalprocesses.

ConclusionThroughout this article, we have attempted to evoke a set of factsderived hom acoustics, psychoacoustics, and cognitive psyohclogythathave a certain resonance with the spectral approach, Through theexample of roughness, we showed how a part of an essential musicalfeature such as dissonance could be embedded In the material itself,involving the knowledge of its acoustic g1'0und1the study of its transfor-mation through perception, and .how it is put into perspective throughthe influence of cognitive processes involved in 'listening. The mutualcuriosity of scientists and musicians is not recent, but it has often. haddifferent motivations. Concerning Q:L~rexample, the question of whycertain intervals are consonant had .sparkad interest throughout history.When Pythagoras WaS, interested in intervals, it took Ute form of a newmanifestation of the omnipresence of numbers ..Later, with Kircher,divi.ne intervention was sought in harmonic ratios. Kepler, Galilee,6. WI?might, hmvever, ask ourselvesif these rules, that actually n~~\dtJl


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Leibniz, Euler, Helmholtz, among others, all made attempts to proposean explanation of their own (Assayag and 01011etoTI , 1995).The goal here is much more modest. To bring this goal to light wewould like to cite a musical custom in New Guinea that is practiced bythe Kaluli of Papua. A ceremony takes place in a hut where the membersof a clan are gathered. Passing vi itor enter the hut at dusk, singing thenames of places they crossed within the territory of their hosts. This songproduces particular reactions among the listeners. Sehieffelin (1979),quoted in Dowling and Harwood (1986), tells the story as follows:'After a while, the audience (the hosts) becomes verydeeply moved. Some 0 , f them, burstinto tears. hen, in reaction to the sorrow they have been made to feel, they jump angrilyand bum the dancers on the shoulders, with the torches used ro.Jight the .eremony. Thedancers continue their performance without showing, ally sign of pain. The dancing andsinging with the concomitant ~ieeping and bmning continue all night with brief restperiods between songs.' (p, 128).Evoking the name of a place to which a tragic memory is perhapsattached (the death family or friends, for example) has triggeredsuch

reactions in the listeners. Obviously, th singer is not interest d inacoustics, nor even in psychoacoustics, and why W01,11d he be so sine heis leaning on external referents to trigger arousals. The point here is thathe knows very little about the referents he is using, being a stranger tothe territory of his hosts. If only the small amount of data concerningmusic perception that have been presented here could be used to avoid'such embarrassing situations. ..

Author note

Th authors would like to thank Joshua Fineberg for providing musicalmateria] as well as useful comments on earlier versions of the manu-script. Correspondence should be addressed to either Daniel Pressnitzeror Stephen McAdams, IR eAM, 1 place Igor Stravinsky, P-7S0Q4Paris,France (email: [email protected]@ircam.fr )..
mailto:[email protected]@ircam.frmailto:[email protected]@ircam.fr

04 Pressnitzer Daniel & McAdams, Stephen - Acoustics, Psycho Acoustics and Spectral Music

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