1. The theatre of spatialisation
I like to make shapes in the head and in the ears, and I also like to make them in the room. (Maryanne Amacher, in Handelman Reference Handelman2010)
Multichannel spatialisation allows the acousmatic composer to dynamically map individual sonic events to locations within a listening space in highly sophisticated ways that were previously impossible when diffusing from stereo sources. The composer is always limited to some extent in terms of where sound can be placed within the space by the architectural (and acoustic) features and by the specifications of the diffusion system. In a typical scenario, the acousmatic composer works outside of the performance space, preparing a multichannel mix from a set number of discrete stems that will be mapped to channels on the diffusion system. These stems correspond to usually 8, 16 or 24 loudspeaker configurations, largely because there is the same number of audio channels available on commercial audio interfaces. Parameters of spatialisation are approximated in the studio, so that strategies for spatiomorphology can be prepared, usually with some basic knowledge of the diffusion system and perhaps a diagram of the listening space. Prior to performance, parameters are then adjusted when the music is first performed in the listening space, usually with a significant degree of compromise and in a short space of time where there is minimal scope to alter loudspeaker positions or reconfigure audio channel routings.
1.1. Site-specific spatialisation
When a composer is fortunate enough to work in the space where the music will be performed, from the beginning of a project, the space becomes embedded within the compositional philosophy and the development of techniques. The composer is able to direct where loudspeakers will be positioned and can access the acoustic properties of the space as parameters within a composition, by creating a diffusion setup which can be used to excite modes at specific frequencies within the space, or which can be used to provide dramatic contrasts between dry and more reverberant (or distant/off-stage) sounds. There may also be opportunities to plan for sounds which appear from above or below the audience, or from hidden locations within the listening space. In this way, the listening space becomes the central feature of a theatrical acousmatic composition in which the space (and loudspeakers) becomes an ‘instrument’ for musical communication with the audience (see Steve Brown, in Brown Reference Brown2010: 173 and Emmerson Reference Emmerson2009: 149).
Such an approach exists of course in audio installations. The benefits of composing for a space can be measured easily in the results of a multichannel work such as Hans Tutschku’s Ailleurs – Intérieur (Tutschku Reference Tutschku2009), composed for the Eglise du Gesù in Montréal and resulting from an extended period of development over several months. Particularly evident in ‘The voices in the nave’ component of the installation is the use of several hidden loudspeakers which are distributed throughout the nave of the church, so that the voices and organ sounds within the work seem to emanate from the statues or pillars, or from the pipes of the church’s organ itself.
The need for extended periods of development to create site-specific sound works of any sophistication was also emphasised by Maryanne Amacher:
To produce the location-based installations for my major works, intensive acoustic and auditory research in the space is required. Usually a residency of one month is needed for my investigations, depending on the size of the space and the number of rooms. During this period I discover special acoustic features of each room, exploring how they interact sonically with each other, and develop the aural imaging and spatial characteristics of the installation. Creating the detailed sound design is very much like scripting a sonic choreography. (Amacher Reference Amacher2009)
A period of development lasting several months is unrealistic for most composers without long-term access to equipment and space, but even one or two days of working in a space with a customisable diffusion system should make a significant difference to the quality of musical results. Signal processing within the studio does not reproduce the visceral experiences and variations in perspective that arise from working directly in the space where the music is to be performed. The dividing lines between acousmatic music composition, theatre sound design and sonic art installation become blurred to the point that any remaining distinctions often seem irrelevant when there is so much shared terminology between the disciplines, although some composers (for example, Normandeau Reference Normandeau2009: 279 or Licht Reference Licht2009: 3) note a difference in the temporal structure of concert works and installations.
This text proposes that techniques for acousmatic spatialisation will function most effectively when developed ‘on location’, with concepts and strategies for spatiomorphology arising from prolonged exploration of the diffusion system within a particular space. Despite the fact that there may be some potential transferability of materials and practice developed for the work to another location, such works are a product of one listening space; a musical counterpart to that environment. The benefits of embedding an investigation of space within the process of composition are that musical and dramatic functions of spatialisation should then be clear to the audience because spatial patterns, interactions and other types of behaviour are presented to them as part of a coherent and audible spatiomorphological strategy.
1.2. The visual theatre of loudspeakers
Loudspeakers also have a visual role to play within the listening space (also see Emmerson Reference Emmerson2009: 147). They are often the only visual link for the audience during acousmatic performances, even in darkness, where LEDs often disclose their locations. One approach is to remove them from sight, as in some forms of theatre practice (Brown Reference Brown2010: 170), where the advantage of invisible loudspeakers is to encourage a more ambiguous perception of localisation and alleviate the natural tendency for audiences to look towards the origin of sounds. Conversely, the visual aspect of the loudspeaker can be used theatrically as part of an acousmatic performance. By making use of a wide variety of loudspeaker types and sizes of enclosure, it is possible to populate the listening space with objects that are both visually and sonically interesting for the audience. From BEAST’s ‘tweeter trees’ (Harrison Reference Harrison1999) or the customised loudspeakers of the GRM Acousmonium (for examples, see Chippewa Reference Chippewa2008) and in many smaller-scale installations, the theatre of loudspeakers is an important aspect of sound diffusion in this context. The dramatic impact of switching the focus of spatialisation from a cheap ‘ghetto-blaster’ to a large, expensive studio monitor (that could be ten times the size of the former) has more than a purely sonic function. Such an action may establish a sense of question–response dialogue between not only two spatial locations, but also between two technological extremes. In this scenario, the loudspeakers may assume personalities within the space as a result of the choreographed movement of sounds by the composer which could be used to reveal cultural, comic or melodramatic elements within the work, for example.
2. The theatre of spatial behaviour
Approaches to spatialisation in acousmatic music are frequently concerned with the creation of an immersive, enveloping spatial environment which may often be related to the ‘global perception of the surrounding sonic environment’ (Lotis Reference Lotis2003: 258). For example, ecological approaches to spatialisation have been proposed where the listener is provided with information to understand the surrounding sonic environment:
In music, ambiophony can be structured in meticulous detail, prepared by the composer in order to emphasise archetypal and global environmental perception. It offers a space in which attention is not guided by isolated or detached sounds, but focuses on larger-scale observation. Hence, the auditor does not localise the sources of sounds but becomes immersed in a diffused ambience. It is the nature of the diffused ambience that defines its archetypal character. (Lotis Reference Lotis2003: 258)
This approach can be highly successful in classic examples of acousmatic music (see Adair, Alcorn and Corrigan Reference Adair, Alcorn and Corrigan2008 for a comparative study of envelopment) and particularly perhaps those works which have roots in stereophonic or 5.1 surround sound. As a result, these pieces are transferable and tend to work effectively both on CD and when performed on a large multichannel diffusion system. Such works lend themselves to an immersive sonic experience which may also include periods of isolated point-source spatialisation to provide dramatic contrast in terms of musical scale and types of spatiomorphology.
The use of multichannel sound diffusion to create both immersive and point-source spatialisation effects has also become an important feature of both experimental and commercial theatre productions. For example, The Royal Exchange Theatre in Manchester uses typically between 70 and 120 loudspeakers rigged on three levels as well as above and below the audience, to immerse them in as much of a 360-degree surround environment as possible and according to the requirements of each production. IOU Productions (IOU 2010) follow a similar philosophy through their productions in outdoor locations. Their production of Waylaid, for example, was staged outdoors inside a portable dome where the large sound system was augmented by headphones for each member of the audience which supplied sounds relating to the inner thoughts and feelings of the central character (Wheeler and Sobey Reference Wheeler and Sobey2007). This approach highlights an interesting use of personal space (Smalley Reference Smalley2007: 48) within a performance that goes beyond the model of surrounding/immersive spatialisation to a multimodal use of space. Similarly, small loudspeakers can be placed underneath seats or very close to the audience without risk of ear damage to create dramatic invasions of personal space and to contrast large spatial gestures with small, intimate sonic events.
From a technological perspective, the limitations of physical control interfaces for multichannel spatialisation have not been completely overcome at this point in time and the studio mixing console in particular, as a relatively crude interface between composer and multichannel diffusion system, has become a serious barrier to the creative ambitions of live sound spatialisation. Certain types of spatiomorphology remain inaccessible to the composer without the use of customised software such as Resound (Mooney and Moore Reference Mooney and Moore2008) or equivalent systems to perform independent rotation of sound sources or other more complex spatial behaviours (see Stefani and Mooney Reference Stefani and Mooney2009: 416–18).
3. Investigating space
It’s unfortunate that music is still presented as it was in the 19th century, frontally, instead of finding new ways of presenting events. There should be fantastic buildings for musical and sound productions. Not just a lot of speakers, but a really extraordinary architecture that you find your way in, that evolves. This will happen because there is a need for it. (Maryanne Amacher, in Handelman Reference Handelman2010)
Most acousmatic concert music will follow a similar layout to the proscenium arch (Theatre Design 101 2009), where a frontal stage area is the focus of attention, with the audience facing forwards towards this point. Usually the stage area is also the focus for the majority of loudspeakers, with a more limited array at the sides and rear. Thrust layouts are similar to proscenium arch stages but tend to have a platform or performance area that extends into the audience space so that the audience is located on three sides, rather than just in front of the performers. Alternative layouts, such as theatre-in-the-round, take the spatialisation of sound even further. Theatre-in-the-round was common in ancient Greek and Roman theatre, but is still often considered as a somewhat experimental formation. Theatre-in-the-round exposes the central section of the theatre space (for a good example of this, see Royal Exchange Theatre 2010), resulting in very few places for sound or loudspeakers to be hidden within set or scenery on stage. The configuration of the diffusion system in this format typically means that loudspeakers are strategically placed around the central audience position in a circular formation immediately in front of the action on stage.
Freedom of movement is important in many examples of sound installation work, where artists such as Bernhard Leitner explore different sonic perspectives created by physical movement within a space. In the multichannel sound installation The Forty Part Motet (A reworking of ‘Spem in Alium’ by Thomas Tallis 1573) by Janet Cardiff, the freedom to move around the space allows each member of the audience to experience the different perspectives of each singer within the choir (Cardiff Reference Cardiff2010) and discover how each voice contributes to the overall composition of the music. In contrast, the interaction of audience and sound diffusion system is limited in most acousmatic performances by the physical restrictions of the performance venue. However, where there is no fixed seating or alternatives to the traditional concert-hall configuration are available, principles from theatre practice and sound installation may be explored in a musical context. The following case studies present approaches to the layout of loudspeakers and performance spaces that are inspired by examples of theatre settings and by installation works which prioritise the sonic investigation of space.
3.1. Symmetrical concert-hall configurations
A typical setup for multichannel spatialisation in a concert hall will follow the established configuration of loudspeakers arranged into stereo pairs throughout the space surrounding the audience area. The frequency response of the system is usually extended by pairs of subwoofers at the front and rear of the space, and perhaps one or more trees of tweeters may be positioned above the audience. The front of the listening space tends to be prioritised by positioning groups of larger ‘main’ loudspeakers in this zone to provide the best quality, optimum ratio of direct sound or accuracy of stereo imaging. More distant locations, particularly at the front and rear of the audience are used to provide a more diffuse sound when required, perhaps by elevating loudspeakers above head height or by facing them away from the audience. Variations of this type of configuration are usually suitable for performance of stereo, quadrophonic, octophonic or 16-channel works (see the Gmebaphone example in Emmerson Reference Emmerson2009: 153) and may be specifically designed to accommodate these formats as standard. The diffusion system can be augmented to accommodate a higher number of channels by adding extra loudspeakers to provide special effects or fill spatial gaps in the listening space.
3.2. Asymmetrical configurations
In a less conventional performance space, where audience positioning may be more flexible than in a concert-hall setting, there is potential to explore more radical loudspeaker configurations. The space may not be rectangular or symmetrical and may have features which make a geometrically proportional diffusion system less relevant. A particular focus in this scenario might be for the composer to look for contrasts in height and distance from the audience, and to find opportunities for sonically interesting point-source loudspeaker placements around the space, with scope for creating immersive effects if required as well.
3.2.1. The proscenium arch as an ensemble space
This proposed configuration focuses upon the stage area within a conventional concert-hall space, where all of the available loudspeakers are distributed unevenly across the stage area and only at the front of the listening space. Here, there is no attempt to engage with notions of immersion (or stereo reproduction: loudspeakers are not arranged in pairs), but instead a solo instrumental view of the diffusion system is adopted, where loudspeakers are individually positioned on stage so that they each point at varying angles and directions outwards towards the audience. Loudspeakers become mono point-sources within the listening space and the distinctiveness of pre-composed material supplied to each point is the most important element of the study: each loudspeaker has its own individual spectromorphological character (reminiscent of the intonarumori) supplied by a discrete track in a multichannel arrangement. What is interesting in this context is the relationship between an individual loudspeaker and its individual sonic character (and musical function) within the ‘ensemble space’ (see Smalley Reference Smalley2007: 41–2), which should be identifiable by the audience. Once the relationship has been established long enough to be clearly understood, it is then possible for the composer to reconfigure the mappings between source material and spatial locations, therefore altering the balance of the music within the space, or performing a spatial remix of individual sonic components within the work. The rate and manner in which this transformation occurs will produce either subtle drifts in the localisation of discrete sounds, or dramatic shifts in perspective.
3.2.2. The inverted thrust layout
In this example, the traditional tiered seating of a concert space becomes the focus of attention, with loudspeakers positioned on each row while the audience stand or sit on the floor of the stage area, facing the loudspeakers. This approach gives the composer the ability to investigate height as the central component of a work, with each row and column of loudspeakers within the diffusion system potentially allocated a distinct musical role within the composition. The audience are encouraged to re-evaluate their relationship with the diffusion system, which no longer assumes the same passive or anonymous role within the performance as they look out from the stage to where they should be seated.
3.2.3. Linear arrays
This study presents a panoramic configuration of loudspeakers distributed evenly in a long line across the listening space and positioned at head height relative to a seated audience directly in front. A suitable space for this configuration would be a long room, corridor or tunnel of sufficient width. The audience is positioned in a staggered line directly facing the loudspeaker array at a distance of between 1 and 2 metres, so that they sit in groups of two or three per loudspeaker. In this case, the compositional focus is upon the diffusion of sounds on a horizontal plane, along which sequences and patterns of sounds may be presented. An obvious instrumental analogue of this spatial configuration would be a performance of handbell ringing. Here, the proximity of the audience to the loudspeakers is particularly important, as this will dictate to what extent the listener is close enough to focus mainly upon a single point along the plane (and where the nearest loudspeaker may be close enough to encroach upon personal space), or at a greater distance, where the listener is able to experience a broader, ‘holistic’ space (Smalley Reference Smalley2007: 37). With this in mind, two rows of loudspeakers (separated by a distance of at least 2 metres), could be employed by the composer to switch between personal and holistic spatial representations of the material as it is diffused along the horizontal plane. The outcomes of this case study are likely to resonate with Smalley’s discussion of ‘enclosure’ and ‘ouverture’:
At one extreme, a process of enclosure implies filling prospective space to the extent that the distal periphery will be absent or masked; there will be an emphasis on proximate space, which may be aided by an impression of magnification … At an opposite extreme, a process of ouverture, whether sudden or gradual, will be initiated by the total or partial erasure of elements within proximate space, permitting the view to expand into distal space, possibly paralleled by an impression of panoramic extension, thereby creating a more open or transparent view which no longer threatens egocentric space. (Smalley Reference Smalley2007: 49)
3.2.4. Non-standard interior spaces
Interior spaces in more unusual locations can provide interesting opportunities for the composer to explore point-source and immersive spatialisation, particularly when the audience are given the freedom to move around the space and alter their perspective of the music. Maryanne Amacher’s work included many potent illustrations of how musical sound could be used to celebrate architectural spaces, such as in her series of Music for Sound Joined Rooms(1980–2002):
Immersive aural architectures are constructed, linking the main audience space sonically with adjoining rooms through specially designed multiple loudspeaker configurations, creating the effect that sounds originate from specific locations and heights rather than from the loudspeakers. The idea is to create an atmosphere similar to the drama of entering a cinematic closeup, a form of ‘sonic theater’ in which architecture magnifies the expressive dimensions of the work. (Amacher 2009)
Ross Brown describes the ‘aural pleasure’ of architecture in relation to the design of theatre spaces (Brown Reference Brown2010: 154) where prominent resonances, reverberation and other sonic features within a space contribute to the audience’s enjoyment of the performance. Spaces with irregular shape that would normally be difficult environments for stereo reproduction can be interesting for the composer when investigating options for point-source placement of loudspeakers in asymmetrical arrangements which may also permit opportunities for greater height variation than would be possible in a typical concert-hall space. In a more unusual space, the composer must also consider how the audience should interact with the work and whether a fixed seating area is necessary to ensure some degree of uniformity in the experience. Many composers may wish to preserve the notion of a static audience, to retain greater control over how the work is perceived and maintain high levels of concentration, which may be difficult to achieve when an audience is mobile.
3.3. Outdoor spaces
When planning multichannel spatialisation in an outdoor setting, careful consideration of the sonic potential of the environment is required: for example the maximum dynamic range (which may be reduced by traffic noise perhaps), natural reverberation/echo, special acoustic features (such as resonant spaces), options for loudspeaker positions throughout the space, and the overall number and size of loudspeakers required to fill the site with sounds at the levels required. Practical limitations may of course also be critical, including access to mains electricity and management of public safety, before the piece can be realised. As an illustration of this process, Memories Unearthed (Lauke Reference Lauke2009) makes use of a disused colliery site in the middle of a large public park. The site was chosen as it offered several special sonic and geographical features for the composer, including different levels above and below ground and places where loudspeakers could be concealed at varying heights along a footpath and around the pit entrance. The paths were used to lead the listener down steep steps to the old Gal Pit, with loudspeakers strategically placed around the top section where the pulley system, which would have once operated the cage, still stands. The diffusion system and layout of the site provided a varying impression of acoustic depth and proximity for the electronically processed sounds, which metaphorically followed the listener downwards from the top of the cage, down to the bottom of the echoing shaft, as though mimicking the journey of the miners to the coal-face.
4. Case studies: spatial composition techniques
Sound spatialisation in live acousmatic performance can provide an explanatory role in the identification of sonic textures, rhythms and forms of musical interaction within composed structures, so that logical patterns of spatial movement may be used to highlight corresponding patterns of rhythm, pitch and spectrum, for example. The following case studies illustrate compositional approaches and experiments which employ spatialisation techniques to enhance or reveal musical features within an acousmatic work.
4.1. Spatial Klangfarbenmelodie
In this example, pitched sounds are organised into monophonic lines (similar in morphology to a melodic line, but here with more drastic variations in spectrum with each event in the sequence) which are then broken up and distributed between individual loudspeakers or groups of loudspeakers positioned around the space. The contour of each Klangfarbenmelodie can be programmed to follow a path through the diffused space, with a specific and identifiable pattern of spatial movement evident in the composition. This technique is possible without sophisticated software algorithms or controllers and can be programmed into a multitrack digital audio workstation, for example. It is therefore possible to associate discrete Klangfarben sounds, arranged as a melodic pattern, with specific spatial locations, or even individual loudspeakers. With repetition, spatial positioning of sounds becomes thematic or motivic (depending upon the length of a phrase), with the potential for thematic variation and motivic development by the composer once a recognisable pattern has been established. A focus upon pitched sounds is important to assist in our perception of spatial patterns and although similar effects will be possible with sequences of unpitched sounds, the combination of pitch and varying spectrum makes recognition of spatial patterns particularly clear (see Davies Reference Davies2010: 17).
4.2. Spatial counterpoint and polyphony
In this model of spatialisation, contrasting musical functions of the listening space are defined by the composer so that specific musical material can be allocated appropriately to discrete zones within the diffusion system, or individual loudspeakers. Once the musical character of each zone within the space has been established, the potential for contrapuntal interactions between zones emerges. As an illustration of this process, in a study of three zones within a listening space, distinctive material is independently devised and allocated to spatially dispersed zones within a large acoustic area surrounding the audience. Simple patterns of musical interaction, such as ‘question and response’ are heard between the zones, in some ways reminiscent of the cori spezzati techniques of early antiphonal works. Once a pattern or behaviour of musical interaction between zones has been established (through repetition), and the audience become familiar with the logic of the spatiomorphology, the composer can then interrupt anticipated patterns of spatiomorphology and expand the range and complexity of interactions between the zones. For example, the composer may alter the speed of spatial movement, and increase the polyphony (i.e. the number of concurrent, interacting spatial patterns) and subsequent textural density of the spatialisation. The lack of familiarity, or potential disorientation experienced by the audience, becomes an expressive tool for the composer, where complex and irregular patterns of spatiomorphology are contrasted with periods of relative spatial stability throughout the work.
4.3. Spatial articulation and dynamics
Sound diffusion has a long-established role in the dynamic shaping of musical lines by skilful performances at the mixing console (particularly from stereo source material), where the performer uses the balance of output channels on the console to dynamically alter the proportion of sound that is sent to each loudspeaker within the listening space. The effect of this is to push sounds away from the audience to a more distant zone within the listening space (perhaps emphasising a diminuendo) or draw sounds inwards from a wider panoramic stereo image into a narrower, central focus, for example. In a multichannel context, the level of control over such dynamic spatialisation increases exponentially as a greater number of simultaneous musical lines and discrete channel-loudspeaker mappings are available to the composer. The dynamic contour of complex musical material can be shaped dynamically via spatialisation within the listening space, where individual lines within a sonic texture may be independently diffused with great precision to accentuate details in a way that would have been impossible to achieve at the mixing console.
4.4. Spatial harmony; unison; tutti!
In this proposed series of studies, spatial harmony is here used to describe concurrence of morphological behaviour across different zones within the listening space. Each zone may be performing a different musical function within the listening space, but the combined effect of all zones is more important musically than the individual components and it may not be possible for the audience to hear significant differences in sonic character between zones. As an illustration of how this may occur in a musical context, the composer can combine several different forms of spatiomorphology into a spatial behaviour that is perceived as a unified circular rotation at a fixed speed of motion around the diffusion system. In this case, the listening space will be heard to gradually rotate in a harmonious progression around the audience, despite the potential variance of material between zones.
In contrast, a spatial unison in this context describes when each zone within the listening space concurs not only in terms of spatiomorphological behaviour, but also in terms of sonic material: each appropriate loudspeaker within the listening space plays the same sound at (approximately) the same time, perhaps with some amplitude variation to enhance the immersive effect. A distinction between unison and tutti is made here: tutti implies that sounds will be heard together, but they are not necessarily the same sound. As a dramatic device, tutti is particularly expressive as a means of suddenly and momentarily unifying the musical performance across the listening space to contrast with periods of more polyphonic music or complex forms of interactions between spatial zones.
4.5. Pitch and pulse
The use of pure tones, pulses, impulses and other simple sounds can be useful in a complex spatial environment, where the objective of the composer is to reveal spatiomorphological techniques clearly to the audience. Aside from any aesthetic reasons for choosing such minimal sounds to work with (and the links to experimental works by artists such as La Monte Young and Alvin Lucier are obvious), the composer may find that creating simple studies in spatial behaviour for use within a space using tones or impulses is a useful exercise before introducing more sophisticated spectra simply because it is often easier to evaluate the acoustic properties of the space in this way. Discovering how particular synthetic tones interact with the modal frequencies of the space may inform subsequent decisions about spectral processing parameters, for example, and synthetic impulses will be useful in judging the potential speed of motion that can be applied to the spatialisation of percussive sounds.
Studies may include investigations of how audible microtonal clusters and small shifts in frequency will be when placed in different zones within the listening space. Tones or simple broadband spectra with varying loudness and envelope characteristics will demonstrate the effectiveness of different attack/decay times as the sounds move within the space. The audibility of spatialised rhythmic patterns, synchronisation of distant sounds and forms of interaction between spatial zones may also be assessed at this preliminary stage of development.
Such experimental work may also find its way into final compositions: using tones to excite resonant frequencies can suggest purity, ritual, physical sensation (Brown Reference Brown2010: 149–162) or simply provide a contrast to music featuring more complex sounds.
4.6. Synthesis and spectrum
What is unique in electroacoustic music is the possibility to fragment sound spectra amongst a network of speakers. When a violin is played, the entire spectrum of the instrument sounds, whereas with multichannel electroacoustic music timbre can be distributed over all virtual points available in the defined space. (Normandeau Reference Normandeau2009: 278)
A cluster of tones (heard as a single timbre) in one area of the space (perhaps from a single loudspeaker) can be gradually decomposed into individual frequency components which are dispersed to individual zones separated by an appropriate distance within the listening space. As a study of timbre and spatial decomposition of additive spectra, this technique can also be applied to resynthesised spectra derived from recorded sounds (for example, Torchia and Lippe Reference Torchia and Lippe2003), where component frequencies are dispersed and reassembled in space. Such techniques of spectral synthesis and decomposition within the performance space evoke notions of Schaeffer’s analytical (or ‘reduced’) listening mode (Smalley Reference Smalley1997: 111), here realised through the process of sound diffusion.
4.6.1. Granularity and space
Granularity is here defined not only as a method of sound synthesis, but as a broader notion (Smalley Reference Smalley1997: 117), which may include spectra derived from granular resynthesis of recorded sounds. By directly mapping granular parameters to spatial behaviours (for example McLeran, Roads, Sturm and Shynk Reference McLeran, Roads, Sturm and Shynk2008) the composer is able to experiment with the continuum between sound texture and rhythm (or pulse) as a manifestation of space. When grain size or time distance between grains is algorithmically linked to spatial distance (including height), so that grain sizes are linked to relative distances between the audience position and the zones within the listening space, for example the sound spectrum can be used to express the flow of spatial movement between two zones. Complex textures may be created when a number of different granular textures are combined to form multiple grain-streams that change in density or evolve from trains of pulses to continuous timbres or tones as they are moved between points within the listening space.
4.7. Soundscapes
A soundscape may be spatially decomposed, or (re)composed in a similar way to an additive synthetic spectrum. The possibility of spatially ‘exploding’ or re-synthesising a soundscape from individual sonic components emerges if the soundscape has been recorded in a multichannel format. Spatialisation in this case can be used to dramatically alter the balance and spatial perspective of the sonic environment. In an ‘exploded’ state, where the components of the soundscape are separated spatially by a significant distance, it may be possible to force them to become abstracted from their context and assume an independent sonic function within the listening space. When these individual sonic components are de-contextualised (by separating them from other sounds that are required to identify them as being part of a real environment), they are revealed in their isolated state as unnaturally loud, detailed or containing an overly broad spectrum to be ‘believable’ components of the soundscape. Filtering, reverberation (including their acoustic equivalents) and other forms of signal processing such as convolution may be used to enhance the effects of de-contextualisation and reintegration within a convincing sonic environment. This technique could also function in a similar manner with synthetic sounds to create impressions of artificial or imaginary soundscapes that are enhanced by the listening space.
Individual elements of a soundscape can be focussed and developed as compositional subjects within a work by relocating them from a distant zone to a location close to the audience, thereby potentially transforming a quiet, background component of the soundscape into an isolated sound object that can be evaluated in detail by the audience and explored in spectromorphological terms by the composer.
4.8. Spatial mapping of DSP
By mapping discrete audio effects busses from computer to dedicated loudspeakers, it is possible to link a specific type of signal processing to a spatial location within the performance space. The basic notion of applying signal processing to particular loudspeaker channels is not new: filtering, delay and reverberation have been used in commercial surround-sound applications to compensate for deficiencies in the home listening environment, to provide an enhanced sense of localisation or to introduce special effects, particularly in surround channels. However, in this context a more radical use of signal processing is proposed to drastically alter the spectrum and morphology of sounds during spatialisation. In one proposed study, distinct impulse responses are applied via convolution to individual audio busses which supply audio to dedicated loudspeaker channels. A single sound source may then be dynamically panned across the available audio busses, so that the sound not only changes spatial location, but also radically changes in spectral character as it moves between loudspeakers. Therefore, a direct mapping is made between a spectral characteristic (provided by the discrete impulse responses) and a spatial location within the listening space. Convolution is frequently used to create realistic reverberation effects, but here its function is to provide a wide variety of spectral transformations that are not limited to the simulation of existing acoustic spaces. Other less computationally intensive types of signal processing such as ring modulation will also provide dramatic variations in timbre when mapped in a similar way.
5. Conclusions
This text proposes an application of multichannel spatialisation to focus upon the spatial exploration (and demonstration) of higher-level concept-driven parameters within an acousmatic composition. The depiction and synthesis of realistic, mimetic or immersive auditory scenes which have been created within a conventional studio space (and which are designed to be transposed to a wide variety of listening spaces) require a degree of uniformity and standardisation in the diffusion system that would contradict the aims of the approaches proposed here. By taking a site-specific approach to composition, with spatialisation (and the individual characteristics of a space) at the heart of the conceptual framework for each study, the theatrical and musical potential of spatialisation can be explored without compromise. The disadvantages of the lack of portability in such an approach are balanced by the potential benefits of developing new compositional techniques for musically coherent multichannel sound diffusion that are informed by an understanding of real spaces.
