Current Technologies and - Recherche en IA spécialisée au MIT

Current Technologies and
Compositional Practices for
Spatialization: A Qualitative
and Quantitative Analysis

Nils Peters,∗ Georgios Marentakis,†
and Stephen McAdams∗
∗CIRMMT—Centre for Interdisciplinary
Research in Music Media and
Technology Schulich School of Music
Department of Music Research
Université McGill
555 Sherbrooke Street West
Montréal, Québec, Canada H3A 1E3
{nils, smc}@music.mcgill.ca
†University for Music and Dramatic Arts
Institute of Electronic Music and Acoustics
Inffeldgasse 10/3
8010 Graz, Austria
marentakis@iem.at

Spatialization, the synthesis of spaces and spatial
properties of sounds for a listener, is a growing field
of interest for researchers, sound engineers, com-
posers, and audiophiles. Due to broad and diverse
viewpoints and requirements, the understanding
and application of spatial sound is developing in
many ways. To benefit from varying viewpoints,
individuals involved in artistic practice and those
involved in theoretical or applied research need
to engage in regular dialogue. Blesser and Salter
(2006, p. 184) reported on the long-term relationship
between artists and audio researchers regarding
virtual spaces, which is “the story of an evolving
relationship between sophisticated audio engineers,
creating tools, and impatient artists, incorporat-
ing such tools long before they are fully defined.”
Otondo (2008) showed that over the last ten years
the technical equipment of composers has improved
both in quality and quantity, with sound spatial-
ization based on five or more loudspeaker channels
being increasingly preferred over traditional two-
channel stereo systems. Novel spatialization tools,
cependant, have hardly found their way out of the
research lab: Artists continue to use conventional
and familiar spatialization techniques. As composer
Natasha Barrett said, “the spatialization equipment
and technology have become readily available, mais
the users haven’t caught up” (Otondo 2007, p. 17).
To effectively guide future research efforts, nous
need to understand this lack of coherence between
development and creative musical application.

Computer Music Journal, 35:1, pp. 10–27, Spring 2011
c(cid:2) 2011 Massachusetts Institute of Technology.

Méthodologie

Dans notre étude, a Web-based questionnaire was de-
signed and presented to composers and sonic artists
to help understand how they use spatialization, what
spatial aspects are essential, and what functionali-
ties spatial audio systems should strive to include
or improve. En plus, we surveyed the degree to
which artists know, and have already applied, récent
developments in spatial audio technologies.

The survey, consisting of multiple-choice and
comment-form (open-ended) questions in English,
was divided into two parts: 13 compositional and
11 technical questions. Unlike the multiple-choice
questions, answering the open-ended questions
was not obligatory. Each multiple-choice ques-
tion included a comment text field to account
for individual responses, and the arrangement of
multiple-choice responses was randomized across
respondents to reduce order effects. To ease the
response-entry process for the respondents, ce
survey was deployed over the Internet and could
be stopped and continued at any time. Open-ended
questions were independently analyzed by two
researchers to control for biases in interpretation.

Respondents

The survey was announced in March 2008 on sev-
eral appropriate Web domains, such as SpACE-Net,
and mailing lists by the Canadian Electroacoustic
Community (CEC), the British Sonic Arts Net-
travail (SAN), the Australasian Computer Music

Computer Music Journal

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Chiffre 1. Geographic
distribution of the 52
répondants.

Association (ACMA), and Norwegian young com-
posers. Plus loin, several invitations were directed
to specific contemporary composers, including the
panelists of the 2008 CIRMMT/UCSD Music +
Technology Incubator III workshop. Responses were
collected for 14 days and 52 surveys were completed
(environ 55 percent of all the surveys that
were started). This response rate can be considered
as very high for a non-reward, Web-based survey,
and suggests demand and interest.

Respondents were primarily male (85 pour cent)
and predominantly from Europe and North America
(voir la figure 1). For musical education, plus que 80
different universities/conservatories were named,
of which the most frequent were Universit ´e de
Montr ´eal (17 pour cent), University of Birmingham
(10 pour cent), and Stanford University (8 pour cent);
several respondents were self-taught (11 pour cent).
Respondents reported an overall composition ex-
perience of 20 years on average, 14 years of which
was computer-aided, et 10 years of which involved
spatialization. Remarquablement, several experienced
composers reported a longer history of using spa-
tialization than applying computer techniques to
their work. Because we expected that work ex-
perience might affect responses, composers were
separated into analytic groups according to their

reported experience in using spatialization tech-
niques: “beginners” (sous 5 années), “intermediate”
(5–10 years), and “advanced” (plus que 10 années),
resulting in equal-sized groups.

Responses

This section presents and interprets the participants’
responses to questions regarding compositional
aspects, the working environment, and the usage of
spatialization tools.

Fields and Forms of Application

To create valid use cases in research and develop-
ment, we asked respondents to specify the artistic
fields and presentation forms in which they apply
spatialization. The upper part of Figure 2 shows that
more than half of the respondents use spatialization
for live electronics and/or for prepared electronics
(fixed media). The “Acousmatique” classification
was added here because several composers explicitly
indicated this category in the comment text field.
Although prepared electronics seem to be equally
distributed among experience groups, one can see

Peters, Marentakis, McAdams

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Chiffre 2. Distribution of
“orchestration” and
contexts in which
spatialization is used as a
function of compositional
experience. Multiple
categories could be
selected. (In this and

similar ﬁgures, le
rightmost edge of an entire
bar measures the total
response percentage across
all three experience
groupes. Within a bar, le
response percentage for a
given experience group is

given by the width of the
corresponding colored
section of the bar, not by
the absolute position of
that section’s rightmost
edge.)

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that in live electronics, spatialization is used less by
“beginners.” One could speculate that a live elec-
tronics project might generally be a bigger challenge
for an artist than a fixed-media production, such that
“beginners” are likely to reduce a project’s complex-
ity by avoiding spatialization. De la même manière, on average
we find fewer “beginners” in the mixed-music cat-
egory (electronics combined with instrumentalists).
An Analysis of Variance (ANOVA) revealed that the
number of orchestrations per respondent increases
significantly across experience groups (F(2, 46) = 5.6,
p < 0.007). More than 90 percent of the respondents present spatial music in a concert situation (see lower section of Figure 2). The second most frequent presentation form is sound installations (more than 60 percent). New media forms, represented through the categories “Web application” and “Film, video” are the least common forms for respondents with more than 10 years of experience. Compositional Motivation and Realization In an open-comment form, we asked composers why they use spatial aspects in music. The comments Table 1. Why Composers Use Spatial Aspects in Their Music Category Total Responses % To enhance the listening experience As a paradigm for artistic expression To organize and structure sounds To experiment with technology and spatial effects Perceptual motivation Segregation and blending of sounds To add motion and dynamism To make sounds more natural and vivid 29 22 20 12 12 11 9 7 58 44 40 24 24 22 18 14 Fifty responses in open-comment form. Respondents chose multiple categories. were sorted and clustered into response categories (see Table 1). Most frequently (58 percent), composers inten- tionally use spatialization to enhance the listening experience. Multiple responses suggest that such an augmented experience is often achieved through immersing the listener in sound. Spatial aspects heighten the experience of space and time and 12 Computer Music Journal therefore “intensify the sensory experience for the listener” per a British composition student. Several artists believe that listeners find it more interesting to hear sounds coming from a variety of directions than from only the traditional frontal stage direc- tion. For almost half (44 percent) of the respondents, spatialization is a compositional paradigm. “There is no other way to express the ideas I am working with,” said a 39-year-old artist who works on spatial sound installations, Internet applications, and con- cert music. Another composer working on prepared electronics for sound installations and film/video said that spatialization is “a subtle but important part of the whole in [his] compositions.” More precisely, a composer who works with Wave Field Synthesis (WFS) said that he is not interested in the accuracy of movement and localization of WFS, but in the way an individual sound can create a space itself without changing acoustical properties of the room, e.g., by using additional reverb. Forty percent mentioned that spatial aspects help to organize and structure music. “The spatial structure of a work may be of equal importance as its organization in terms of pitch, timbre or rhythm,” stated a composer who primarily presents fixed-media pieces within a concert situation. Another mentioned that spatialization “adds one or more artistic layers to a piece.” A quarter of the responses (24 percent) indicate that many composers are attracted to the experi- mental and exploratory side of spatial effects and spatial sound technology. One composer reported that in spatialization “there is still lots of room for innovation, which I like.” Another composer working in the field of live electronics said that spatial parameters are available a priori in the world of computer music and therefore have to be at least considered. Experienced composers are also attracted by the novel possibilities spatialization offers. “Spatialization gives the composer the means to expand their gestural palette into the spatial domain in a dynamic way not previously possible.” Nearly a quarter (24 percent) of the respondents replied that spatial aspects are perceptual attributes of hearing sounds and music. “Life is spatial, mu- sic is spatial”—therefore those attributes should be addressed in music. Composers also explicitly identified the use of sound segregation and sound blending, key concepts of auditory scene analysis re- search (Bregman 1990; Harley 1998), as a motivation for spatialization (22 percent). A composer working for more than 5 years with spatialization said he can “present more sound material at the same time without losing . . . clarity,” while others feel that “complex music becomes more comprehensible.” Respondents also mentioned that spatialization is applied to add motion and dynamism (18 per- cent) or to make electroacoustic sounds more real and vivid (14 percent), “to give sounds an identity.” Very often, composers simultaneously addressed several of these response categories. For a more comprehensive understanding, we studied these intercategorical relations and found a strong connec- tion between the three categories “To enhance the listening experience,” “As a paradigm for artistic ex- pression,” and “To organize and structure sounds.” Many responses that addressed “To experiment with technology and spatial effects” also relate to these three response categories and indicate how strongly experimentation permeates current spatial music. Furthermore, “Segregation and blending of sounds” is strongly connected with “To organize and structure sounds” and “To enhance the lis- tening experience.” Sound segregation is known to facilitate a listener’s processing of compositional structure. Continuing the previous question, we asked how composers configure sound elements to realize spatialized sound experience. If developers knew more about such methods, development could be better applied and could, for instance, increase the usability of spatialization tools. This question trig- gered a variety of unique responses that are related to musical context and site-specific aspects, and are therefore hardly generalizable. The responses (see Table 2) mainly addressed methods for moving sound sources and their distribution in space, and could involve experimentation with the sound ma- terial and the acoustics of the listening room. Often these methods are used to achieve a contrasting perception of sounds (i.e., clarity vs. blurriness, close vs. far, reality vs. surreality, thick sounds vs. thin sounds, dense vs. open). Peters, Marentakis, McAdams 13 l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 Table 2. How Do You Conﬁgure Sound Elements to Achieve Spatialized Sound Experience? Category Example Distribution Distance and depth and position Algorithmically generated distributions Spatial organization according to timbre, texture, and musical function Spatial granularization Stereo tracks as source material Diffuse sounds (multi-speaker distribution) Mono sound reproduced from one or two adjacent loudspeakers Size of the spatial image Planes, subspaces and hierarchical sound layers Front (stage) is the focal point Slight movements Contrast static vs. dynamic Many movements with a small number of sounds Strength of movements according to musical function: melody moves more than other sounds Prepared trajectories Instrumentalists move during composition Live performers moving loudspeakers Changing loudness and dynamics Spectral filtering Reverberation Simulating room acoustics Surreal spatial impressions Movements Others Forty-seven responses in open-comment form. Working Environments In the Composition Studio Figure 3 shows how often various reproduction systems are used in a composition studio. Possible responses were limited to a list of reproduction se- tups according to the frequency categories: “never,” “seldom/sometimes,” “usually,” and “always.” As the main reproduction system in a composition studio, 35 percent of the composers “always” use a two-channel stereo loudspeaker setup and 20 percent “always” use headphones. Multi-loudspeaker ar- rangements, such as quadraphonic or 5.1, are gener- ally used only “sometimes” or “seldom.” More than 50 percent of the composers “never” use, or do not have access to, seven- or eight-loudspeaker configu- rations. Because stereo and headphone reproduction is so common in the compositional phase, one might speculate whether, instead of using expensive multi-loudspeaker setups, composers use binaural or transaural processes to spatialize audio around their head with only two audio channels while composing. Composers’ responses to a question concerning whether binaural or transaural versions of their spatial music have been released suggest that these techniques are rarely used. At the Venue Most composers (76 percent) consider the loud- speaker arrangement in the performance situation as different from their studio environment. Very often, a venue is equipped with more loudspeakers than the composer’s studio. An acousmatique composer said “I have eight loudspeakers in my studio, but most of my work is intended for sixteen loudspeak- ers, and more recently, for twenty-four speakers. The eight loudspeakers in my studio give me an idea.” Another said that he works in a variety of composition studios with two to five loudspeakers, whereas he performs in venues with more than 50 loudspeakers. In contrast to reproduction systems found in composition studios, an eight-loudspeaker array is presently the most common loudspeaker configuration in venues and electroacoustic music festivals (Lyon 2008). However, loudspeaker setups also differ in terms of sound quality and in the hor- izontal and vertical distance between a listener and the loudspeakers. Several composers mentioned that their studio is acoustically treated to minimize the effect of room reflections, in contrast to the perfor- mance venue, where reverberation can be expected. The most common venues are traditional concert halls, specialized venues for electroacoustic music, and gallery spaces (see Figure 4). It is surprising that cinemas are not generally used, as they provide standardized (e.g., the THX standard) acoustic treatment and multichannel loudspeaker systems. On average, composers work in approximately four 14 Computer Music Journal l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 Figure 3. For composing spatialized music in your studio, how often do you use the listed reproduction systems? Figure 4. In what kind of venues are your spatial compositions performed? Others = bars and clubs, classrooms, spatial audio labs, virtual reality caves, spaces with remarkable acoustics. l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 <5 years 5 to 10>10 années

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N

Overall average

Mean response
Most frequent response

40
60
50
Response percentage

100

< 5 5 − 10 Experience in years > 10

Chiffre 3.

Cinemas

Others

Churches

Outdoors

Domestic rooms

Theaters

Art Galleries

Specialized venues for EA

Traditional concert halls

Chiffre 4.

different kinds of venues; this number increases
with more experience (voir la figure 4, droite).

Artists were also asked about the main challenges

venues posed to their compositional aspirations
(see Table 3). The main challenges are related to the
acoustic conditions, to technical limitations of the
venue, and to time constraints within the venue.
For the acoustical conditions, challenging attributes

of venues are room dimensions, raked seats (c'est à dire., un
inclined floor), modes and resonances, and too much
reverberation, which dominates the perception
of spatial elements in a composition and causes
microphone feedback for live electronics. Le
“sonic leakage” from one exhibition to another is an
additional problem for sound installations. Regard-
ing the technical limitations, the main complaint

Peters, Marentakis, McAdams

Tableau 3. What Are the Main Challenges of Venues
You Have Faced so Far with Respect to Your
Compositional Aspirations?

Category

Acoustical conditions
Technical limitations of the venue
Time constraints
Non-ideal loudspeaker

and audience location

Staff and audience
Sweet spot
Cost of production
No problems

Total
Responses

20
16
13
13

8
7
2
3

48
38
31
31

19
17
5
7

Forty-two responses in open-comment form.

was the limited number and quality of loudspeakers.
Nearly one response out of three reported that the
time allocated for arranging and optimizing the
loudspeaker configuration at the venue is too short.
Plus loin, non-ideal locations of loudspeakers with
respect to the audience and a small listening area
(sweet spot) were reported. Many venues have room
dimensions that complicate the setup of equidistant
loudspeakers, as required by most spatial rendering
algorithms. Composers who work with elevation
and height face the difficulty that loudspeakers are
often configured in a horizontal-only arrangement;
hanging loudspeakers is almost always impossible
in traditional concert spaces and opera theaters.
It was reported that venue managers, without the
agreement of the composer, repositioned the seats
of the audience or placed extra furniture in the
venue. This resulted in seats being too close to
loudspeakers and walls, degrading the sound quality
for listeners. Sometimes an ideal placement of
loudspeakers may not be possible due to aesthetic
constraints of the stage or lighting designer.

Because of the diverse reproduction conditions

across venues, artists have developed (composi-
tional) strategies to adapt their work. “I tend to
accept the effect of venue as part of the concretiza-
tion of my ideas,” said an artist who performs in
traditional concert halls, specialized venues for
electroacoustic music, and art galleries. Other com-
posers reduce their technical requirements from the

début, thereby limiting the spatial possibilities.
“As I have moved more towards visual arts, J'ai
discovered that even getting adequate stereo play-
back in a venue is problematic. I certainly don’t try
for anything beyond 5.1,” explains an Australian
artist. Some responses suggest that composers tend
to work with more extreme and obvious spatial
properties, such as heavy panning rather than using
more subtle spatialization techniques, to ensure that
at least these gestures will be perceived. Composers
of fixed-media pieces create different versions to
account for different loudspeaker arrangements.
If there are more loudspeakers than tracks, quelques
tracks may be assigned to more than one loud-
conférencier. Donc, “the more the number of tracks,
the less the adaptability” according to one artist.
“In the studio, I usually use a stereo system. À
the performance place, I then adapt my work to
the diffusion system,” added a Canadian composer.
An Austrian composer simulates “real-world condi-
tion[s]” by using outdoor loudspeakers in his studio
when he works on outdoor installations.

Preservation of Spatial Music

The preservation of electroacoustic music is an
increasingly important topic and is especially
challenging when spatialization is involved. Ainsi,
this questionnaire addressed media formats and
notation practices.

Media Formats

One multiple-choice question asked what media
formats are used for publishing spatial music. Le
two-channel audio CD is the most common medium
(80 pour cent), and all other formats are used by less
que 40 percent of the respondents. Fait intéressant, le
average respondent uses DVD, currently the most
common medium for multichannel audio work, comme
often as conventional two-channel MP3. It should
be mentioned that in a sound installation project,
par exemple, a two-channel recording is often made
mainly to serve as documentation. One composer
mentioned that he will use the “good old audio CD”
until there is a proper storage standard for multi-
channel files. Spatial music is also often stored on

Computer Music Journal

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data DVDs that contain either (1) PCM audio files for
each individual loudspeaker feed (fixed media) ou (2)
the composition within the audio software project
files. An acousmatique composer, l'un des 10 par-
cent who do not use any media, stated, “Publication
is not important for me, I mostly work for live per-
formance.” The level of experience does play a role
in choice. Only those in the “beginners” group were
found to use MP3-surround, a technology to encode
spatial audio in a conventional MP3 file. Another
respondent anticipates that fixed media will fade
away in a few years in favor of sound files on generic
media that can be adapted for different listening
scenarios.

Notation

Through scores, compositions can be stored, ex-
changed, studied, and performed, but also revised
and adapted after their initial creation. To the
authors’ knowledge, there is no common notation
format or standardized vocabulary to describe spatial
parameters (see Kendall and Ardila 2008; Kendall,
Peters, and Geier 2008). Donc, it seems rea-
sonable that 62 percent of the respondents do not
use notation for spatial aspects. Most composers
argued that for (fixed) tape music, there is no need
for a score, or they haven’t found a satisfying way
to notate spatialization. Others said that there is
no score because spatialization is created through
improvisation and experimentation or generated
by real-time algorithms. Composers seem to have
developed individual spatial notations, ranging from
photos and drawings over diffusion guides, to poems
and descriptive text, to sonograms of the music with
annotations. Notation forms also depend on the
production environment. When working in media
programming environments such as Max/MSP or
SuperCollider, spatial parameters are stored in data
arrays within the composition patch, in contrast to
digital audio workstations (DAWs), where built-in
track automation is used to store and recall parame-
ter changes. “When working with the WFS system,
the drawings become one of the main parts” was
a response that suggests that the notation scheme
and the technical environment, including rendering
concept, can influence each other.

Artists and Their Spatialization Tools

We are interested in what composers think about
the software and hardware tools they use for
spatialization, and how their feedback can affect
future development. We are also interested in the
degree to which composers are aware of recent
developments in spatial audio technologies. Chiffre 5
shows the responses to the question “What software
and hardware tools have you used for spatial
compositions?” according to the categories: Never
heard, Heard about but never used, No longer in use,
Currently in use, and Planning to try it. The list of
spatialization tools, which the authors assembled
by reviewing spatialization applications, is a mix of
concepts and products. The experimental approach
to spatialization (Tableau 1) is supported in the choice
of tools: 20 percent of all respondents use self-made
or custom-made tools and 31 percent use a media
programming environment such as Max/MSP or
SuperCollider. The primary spatialization tools are
the built-in panning devices of DAWs and audio
sequencers (75 pour cent) and panning performed
with a hardware mixing console (58 pour cent). Il
seems that older technologies, such as the panning
potentiometers (pan-pots) in mixing consoles, sont
well known, but many are no longer used (dans
case of pan-pots, 37 percent of the respondents no
longer use hardware mixers). De la même manière, IRCAM’s
Spatialisateur, under development since 1991 (Jot
1999), and VBAP (Pulkki 2001) depuis 1998 are widely
known, but are also often replaced by other tools.
The categories “No hardware” (41 pour cent)
and “No software” (33 pour cent) also account for
composers who work with instrumentalists and
without any electronics. It is surprising to see that
several respondents are planning to work without
software. Does that mean that they are frustrated
with current spatialization tools? The categories
“Panning with mixing console” (58 pour cent) et
“No hardware used” (41 pour cent) formulaire 99 percent of
the responses, and artists show little awareness of
other hardware-based spatialization tools.

According to Figure 5, the rendering concepts of
first-order and higher-order Ambisonics (HOA) seem
to be the most interesting techniques for future com-
positions. Cependant, people currently seem slightly

Peters, Marentakis, McAdams

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Chiffre 5. What software
and hardware tools have
you used for spatial
compositions? The longer
the vertical line under the
bubble, the less the
composer continues to use
this tool. The bigger the
bubble, the more the

composer plans to try it.
M3S = Sonic Emotion M3S
WFS system; TiMax =
TiMax Audio Imagine
System; IOSONO =
IOSONO WFS system;
Vortex = Vortex Surround
tools; ViMiC = Virtual
Microphone Control;

SUG = Space Unit
Generator; VSP = Virtual
Surround Panning in
Studer-digital mixer;
S6000 = TC-Electronics
S6000; Zirkonium = ZKM
Zirkonium; Holophon =
GMEM Holophon tools;
DBAP = Distance Based

Amplitude Panning;
Waves 360o = Waves 360o
Surround tools; VBAP =
Vector Base Amplitude
Panning; HOA = Higher
Order Ambisonics; WFS =
Wave Field Synthesis;
Spat<= IRCAM Spatialisateur. l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 more aware of Wave Field Synthesis (Rabenstein, Spors, and Steffen 2004) than Ambisonics. Although HOA and WFS are both high-resolution spatial sound reproduction techniques that are conceptually based on the physical reconstitution of a wave field (Spors and Ahrens 2008), one wonders what makes HOA more attractive. Might it be Ambisonics’ ability to store spatial audio material independently of the reproduction setup? Or, is it that by defining the “Ambisonics order” and choosing the number of loudspeakers, the size of the listening area can be scaled to different listening scenarios? WFS requires a large number of loudspeakers and their spacing creates perceivable artifacts throughout the listen- ing area. By using a periphonic loudspeaker dome, Ambisonics can reproduce elevated sounds, which is an important feature for many composers (as will be seen later in Figure 7). To our knowledge this feature is not currently supported by available WFS systems. Moreover, WFS systems are still rare. Approximately 20 research labs and about 20 auditoriums are equipped with a permanent WFS system (De Vries 2009). Ambisonics systems may simply be more easily accessible to artists. There are several Ambisonics tools up to eleventh order that are freely available (e.g., Schacher 2010). Although these Ambisonics tools do not work in high enough Ambisonics orders as to compete with WFS’s sound reproduction abilities, composers can adapt to the Ambisonics concept by using lower-order forms in production studios and for concert performances (F ¨arber and Kocher 2010) and can more easily switch to higher-order systems in the future. However, the small number of loudspeakers that are currently used in composers’ studios (Figure 3) suggests that more loudspeakers are required for these new spa- tial rendering concepts (e.g., WFS and HOA) to be applied. Despite the greater interest in HOA, WFS offers many compositional possibilities (see Baalman 2007). In contrast to HOA, if an artist only wants to present sounds from one side (e.g., from the front), loudspeakers do not have to surround the audience—an economic, aesthetic, and pragmatic argument. A composer working mainly with WFS systems reported that “the most interesting aspect is not the accurate movement of sounds nor their localization, but the way that an individual sound can create a space itself.” Besides these concepts and products, the survey revealed that many tools are unknown to the majority of artists. Are most users satisfied enough with their current choice of tools and not looking for 18 Computer Music Journal Table 4. What Is Your Motivation for Working with Your Current Spatialization Equipment (versus Using Other Tools)? Motivation Total Responses Usability, learning curve Quality of spatialization, fit to aesthetic goals Availability, accessibility, and cost Flexibility, versatility Integration into existing technical framework Reliability Other 20 15 15 12 7 6 2 Forty-two responses in open-comment form. % 48 36 36 29 17 12 5 other (perhaps more suitable) tools? Do composers rely mainly on audio sequencer software with integrated common spatialization features? Choice of Tools A composer’s rationale for choosing his or her current spatialization tools provides insight into those choices. The responses, in comment form, are analyzed and grouped together in Table 4. Almost half of the responses are related to the usability of tools. Common replies include “simple,” “intuitive,” and “easy to use.” Also, the challenge of learning how to use a tool is included in this category. Sixty-one percent of respondents think the time spent with spatialization tools could be reduced with optimization. The importance of time and usability are likely connected to the pressure composers feel to meet commission deadlines and to maximize work and creative outcomes within limited studio time and resources. People who invest time in creating their own spatialization tools reported that self-written software enables a personal approach to spatialization. Further, the user has control over all the essential parameters, suggesting that ready-made tools might be lacking in this respect. Half of the respondents use fewer features than their spatialization tools offer. Thirty- six percent of respondents base their choice of tools on the degree to which a specific tool can be applied in achieving compositional and aesthetic goals. Responses to another question revealed that 30 percent of the artists are constrained by the number of sound sources that can be spatialized using their current palette of tools. Besides trying less limiting and more appropriate tools, faster and multiple CPUs will also help these composers. Flexibility and versatility were mentioned in 29 percent of the responses, whereas only 12 percent addressed the reliability of their tools. As reliability seems funda- mental, we expected more responses for this aspect. Importance of Technical Features We asked respondents to rate the relative importance of ten technical features for their work using five categories: “Not” important, “Slightly,” “Fairly,” “Very,” and “Extremely” important. The ratings result in relatively little variance; all technical features having an average around “fairly” important (see Figure 6, left). The feature “Spatial rendering in real-time” received the highest ratings (“very” important), whereas “Visual 3D representation of a sound scene” was rated lowest (less than “fairly” important). The most frequent responses demonstrate that there are three features rated as “extremely” important: “Integration into digital audio workstations as plug-ins,” “Controllability via external controller,” and “Spatial rendering in real- time.” To the provided feature list, respondents added properties such as “Level visualization of each speaker feed,” “Up- or down-mixing to eight output channels,” “Managing trajectories, patterns, and direct control protocols within a database,” and “Adaptation to different loudspeaker configurations.” Some of the technical features correlate moder- ately with each other (Spearman correlation ρ(52) ≈ 0.5). A cluster analysis was performed on the indi- vidual responses in order to group technical features together that were similarly rated (see Figure 6, right). This cluster analysis suggests technical features that developers might want to conjointly address for different use cases (indicated with dashed lines in the figure). For instance, a spatialization tool that can be integrated as a plug-in into DAWs should Peters, Marentakis, McAdams 19 l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 Figure 6. Rate the importance you attach to the listed technical features. l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 be equipped with a graphical user interface, whereas an application that renders a spatial scene in an audio-file in non-realtime should be equipped with a visual representation of the sound scene. Another grouping of features addresses real-time rendering in combination with external controllers and the ren- dering of non-standardized speaker configurations. The advantage of real-time rendering is that spatial parameters can be manipulated, e.g., via a gestural controller in real-time (Marshall et al. 2006). Fur- thermore, the rendering process can be adapted to accommodate a given loudspeaker arrangement and certain acoustic conditions. Desired Features When asked if features were missing, 41 percent responded “Yes” and 20 percent said “No.” Often an improvement in the usability of the spatialization tools was requested, such as “intuitive interfaces . . . to control spatialization processes from a high level” or “scalable interfaces that can go from 2 to 500 channels.” Another respondent wished to draw trajectories for multiple sound sources in one scene editor, rather than having multiple trajectory editors, one for each audio track, in a DAW. Others addressed the bus architecture in the DAW application, which often limits the number of loudspeaker feeds: “I prefer to use commercial DAW software, . . . but find most of the available multi-speaker tools inflexible and too cinematic.” Another composer said that DAWs are too inflexible for live work and non- standardized playback scenarios. He misses features that facilitate flexible routing and control of stereo planes to various speaker sets. Generally, a higher degree of flexibility was requested. One respondent said that each tool has strengths and weaknesses, and it is very difficult for him to imagine a tool that does everything perfectly. To benefit from the power of individual tools, he proposed a framework that interconnects them. This might appeal to another survey respondent who wants to map parameters of time, pitch, timbre, and space in his music “through expressive software tools.” Others would like to have tools that help to adapt music to the varying acoustical and technical situations of the performance venues. Lastly, respondents expressed the desire to easily apply different interface devices for controlling spatialization, e.g., for drawing trajectories of sound sources. Besides using common 20 Computer Music Journal Figure 7. Rate the importance you attach to the listed spatial feature. (Features are listed in an order determined by the cluster analysis on the right side.) l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 human–computer interfaces, such as a joystick or keyboard, it was suggested to develop input devices that are tailored to the specific needs of controlling spatialization, for example, multi-touch interfaces to visualize and control multiple spatialization parameters simultaneously. Analysis In this section, we statistically analyze a subset of the responses to relate technical and compositional aspects to each other and to identify potential areas for further research and development. Spatial Aspects: Compositional Importance and Their Fulﬁllment We provided a list of 15 spatial aspects to discover which ones artists consider to be important, and to what degree they can be effectively created through their tools. First, the importance of spatial aspects was addressed and the responses were categorized as: “N/A,” “Not,” “Slightly,” “Fairly,” “Very,” and “Extremely” important. The distribution of responses was: “N/A” 6 percent, “Not” 10 percent, “Slightly” 17 percent, “Fairly” 20 percent, “Very” 24 percent and “Extremely” 23 percent. Hence, almost half the ratings were extremely or very important (see Figure 7, left). Some composers mentioned that the degree of importance can change according to the compositional situation and the musical material. Other comments provided additional aspects not included in this question, such as “Spatial clarity and density,” “Spatial perspective,” and “Spatialization of timbre.” The highest rated spatial aspects are “Immersiveness,” “Distance perception of sound sources,” and “Localization accuracy of sound sources.” The aspect “Large listening area,” a feature of the high-resolution reproduction techniques WFS and HOA, was rated as “very” to “fairly” important. The aspects of “Avoiding” or “Simulating a Doppler effect,” a natural pitch change of fast-moving sounds, were surprisingly rated as least important. Considering that artists who were new to WFS reported disturbing sound coloration when moving sounds, one would have expected this feature to be rated with a higher importance. The higher ratings of Peters, Marentakis, McAdams 21 Figure 8. How satisﬁed are you with the ability of your preferred spatialization tools to produce the listed spatial aspects? (Features are listed in an order determined by the cluster analysis on the right side.) l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 “Creating slow, subtle movements of sound sources” compared to “Creating fast movements” suggest that the unwanted Doppler effect might occur less due to the preference for slow movements, which minimize this percept. The aspect “Virtual sources within the audience” (also associated with WFS and HOA) was rated similarly to “Elevated sound sources” as “fairly” important. The right panel of Figure 7 visualizes the cluster analysis according to a Spearman correlation be- tween the features, computed from all individual responses. “Distance perception” of sound sources was very similarly rated to “Adaptable apparent source width” and also to the aspects concerning the creation of room impressions, e.g., through syn- thetic reflection patterns. Another interesting clus- ter was created from “Elevated sound sources” and “Localization accuracy,” suggesting that composers favoring accurate localization are also interested in perceiving elevated sounds. Remarkably, “Immer- siveness,” the highest rated aspect, is unrelated in this analysis to any other presented aspect. After rating the importance of spatial aspects, respondents were asked to rate in a similar way their satisfaction with the ability of their spatialization tools to (re)create those spatial aspects. The inten- tion behind this question was to determine whether there is a gap between the creative desire and the ability to achieve compositional aims with available tools. The distribution of the responses among the satisfaction categories was “N/A” 18 percent, “Not” 8 percent, “Slightly” 14 percent, “Fairly” 23 percent, “Very” 27 percent, and “Extremely” satisfied 9 per- cent (see Figure 8, left). On average, 6 of the 15 listed spatial aspects that can be produced by the currently used tools were rated “very” satisfactory. Five as- pects have mean ratings below “fairly” satisfactory: “Elevated sound sources,” “Virtual sound sources within the audience,” “Simulation of a specific room acoustic,” “Simulation of an instrument’s di- rectivity,” and “Adaptable apparent source width.” As previously described, a cluster analysis was performed on the ratings. The resulting dendrogram (see Figure 8, right) shows similarities to the cluster 22 Computer Music Journal Figure 9. Spatial aspects, comparison of Importance and Satisfaction ratings from three different composers. Composer A: 1 year of experience; Composer B: 8 years of experience; Composer C: 30 years of experience. l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 analysis of the importance ratings (see Figure 7), that is, aspects regarding the Doppler effect and source movements were also found to be correlated. Comparison In comparing the average responses in Figure 7 with those in Figure 8, one sees that generally the satisfaction ratings are lower than the associated importance ratings. Figure 9 yields insight into the inter-individual differences by showing the ratings of three composers with different levels of spatialization experience. The slight tendency is that with more experience, the differences between importance and satisfaction ratings increase. “Noth- ing is perfect—dissatisfaction is a state of mind” commented composer C from Figure 9. In contrast, a generally satisfied artist with fewer years of expe- rience than composer C said that he can usually get adequate results. His two most important spatial aspects are “Immersiveness” and “Creating slow subtle movements of sound sources.” Spatial aspects rated with the highest “Impor- tance” but with low “Satisfaction” indicate a Table 5. Confusion Matrix Showing the Regions of Interest Satisfaction Not Slightly Fairly Very Extremely e c n a t r o p m I Not Slightly Fairly Very Extremely + + + + + “+” symbolizes cells with the best values in Importance and Satisfaction; “ ” symbolizes cells related to a low Satisfaction but high Importance. demand for better tools and, therefore, more re- search, innovation, and development. Table 5 shows the region of potential research and development interest (marked with “ ”). The responses are sorted according to this confusion matrix. For instance, composer A’s rating of the “Large listening area” shown in Figure 9 fits into a +-region (“very” im- portant and “very” satisfied), whereas composer C’s rating would be sorted into a -region (“very” important and “slightly” satisfied). Peters, Marentakis, McAdams 23 Figure 10. Spatial aspects: All responses are sorted according to importance and satisfaction ratings. The bar height indicates the number of responses in a given category. Figure 11. Spatial aspects: Top part of the plot shows items within the cells marked with a + according to Table 5, whereas the bottom part shows items within the cells marked with a (y-axis = number of responses). The barplot also shows the responses according to the experience groups. l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o m j / l a r t i c e - p d f / / / / 3 5 1 1 0 1 8 5 5 6 1 2 / c o m _ a _ 0 0 0 3 7 p d . j f b y g u e s t t o n 0 8 S e p e m b e r 2 0 2 3 Figure 10. 30 25 20 15 10 5 0 0 5 10 1515 Figure 11. <5 years 5 to 10 years >10 années

↑ Number of items in the cells that have high ratings in Importance and high ratings in Satisfaction ↑
↓ Number of items in the cells that have high ratings in Importance but low ratings in Satisfaction ↓

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Chiffre 10. The higher the blocks, the higher the num-
ber of responses in this “Importance”/“Satisfaction”
catégorie. One can see that many ratings were
given with the combination “extremely” impor-
tant/“very” satisfied and “very” important/“very”
satisfied (lower right corner). The middle-ground

responses “fairly” important/“fairly” satisfied and
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quent. The -region in Table 5 represents more than
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of all responses. An examination of these response
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Chiffre 11. In the -region (voir la figure 11, bottom),

Computer Music Journal

the aspects with the most responses are “Elevated
sound sources,” “Distance perception,” and “Vir-
tual sound sources within the audience.” In the
+-region (voir la figure 11, top), the most frequent
aspects are “Creating slow subtle movements of
sound sources,” “Localization accuracy of sound
sources,” and “Immersiveness.” The latter two
aspects were also judged with very high importance
ratings (voir la figure 7). Localization of sound sources
is traditionally a strong field in psychoacoustics (par exemple.,
Blauert 1997) and much research on spatial audio
reproduction has evaluated this aspect (par exemple., Pulkki
and Hirvonen 2005). The analysis of the composers’
responses suggests that research and development
efforts have benefitted the field of musical ap-
plications. Fait intéressant, the aspects “Distance
perception of sound sources” and “Creating unreal
room responses” have relatively similar contribu-
tions in both regions, indicating a polarization of the
réponses. An analysis of these responses did not
reveal the use of any particular spatialization tool
as a potential explanation. Cependant, the number of
tools a respondent uses affects his or her satisfaction
ratings; two or three tools are more satisfying than
un, but six may not be.

Conclusion and Recommendations

The high response rate of this survey suggests
that this kind of questionnaire is well received
by artists. Researchers from related fields might
be encouraged to similarly gather feedback from
artistes. The responses of 52 composers regarding
technical and compositional aspects were analyzed
to find general tendencies in current usage, alors que
acknowledging the artistic individuality of each
composer. Based on our interpretation of the survey
findings, we derived the following recommendations
for collaborative work between composers and
chercheurs.

The technical and practical challenges of mul-
tichannel sound reproduction systems experienced
by artists often relates to an under-utilization of
available spatial features. To address these chal-
lenges, one has to acknowledge the higher technical
complexity of multi-loudspeaker setups, especially

the emerging high-quality spatialization techniques
WFS and HOA, which require careful calibration
of the equipment for full compositional advantage.
To familiarize composers with new technology, le
learning curve must be kept reasonably shallow
(c'est à dire., gradual). Good usability (par exemple., avoiding cum-
bersome command line control) and the possibility
of integrating new tools into common composi-
tional environments are paramount and can lower
the entry barriers for artists. Many DAWs (le
most commonly used compositional environment,
Chiffre 5) are limited to eight-channel spatializa-
tion. To accommodate the needs of high-quality
spatial rendering concepts, the bus architecture
must be extended to allow for massive output
chaînes.

We also saw the demand for technology to give
composers a feeling of the venue acoustics while
working in the studio. Regarding new technologies,
a number of responses suggest that some artists are
motivated and technically experienced enough to
explore the artistic potential of new or unreleased
tools and become “early adopters.” Real-world loud-
speaker setups often differ from the standardized
systems usually employed in listening experiments.
More ecologically valid speaker configurations in
the labs yield more meaningful data that better
generalize to real-world conditions. The first part
of the survey tells us where, why, and how spatial
concepts are applied, and this information can be
used by researchers and developers to create, dans
the labs, meaningful test environments that ap-
proximate real-world scenarios. Composers could
support this effort by making parts of a composi-
tion accessible to researchers and by supporting
the development of spatial-notation or description
systems as proposed by Kendall, Peters, and Geier
(2008). Apart from increasing the potential of pre-
serving compositions, a common description format
could let developers more authentically re-render
spatial music and evaluate novel rendering methods
or loudspeaker configurations. It is necessary to
investigate how diffusion practice, as a prominent
form of sound spatialization, can be incorporated
into notation/description approaches.

In this article we have analyzed a survey of the
compositional use of spatialization by composers.

Peters, Marentakis, McAdams

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The purpose of the survey was to give an overview of
the current state of practice in order to guide future
research and development of spatial audio systems.
Because the questionnaire was presented in En-
glish, we acknowledge that language barriers might
have created a bias, leading to an underrepresenta-
tion of African, Asian, and South American artists
(voir la figure 1). Cependant, because the respondents
showed a great diversity in composing experience,
âge, and place of education and residence, we be-
lieve that the responses represent a meaningful
cross-section of composers’ views on compositional
and technical aspects of spatialization. Besides the
expected individual differences in composers’ re-
sponses, we also extracted common themes in moti-
vation, compositional practice, preferences, and cri-
tiques of available audio technologies. We hope that
our findings will help enable communication be-
tween artists and researchers in order to refine future
spatial audio technologies that will enhance future
artistic practice. As a side note, although the survey
took place in 2008, the data are still relevant: com-
posers have directly addressed how time-consuming
it is to change from one tool to another. Besides men-
tioning steep learning curves, they clearly operate on
tight deadlines, which leaves little time for explor-
ing alternative and novel technologies. Cependant,
the interest in tools that fit their needs is high.

Remerciements

This work was funded by a grant from the Canadian
Natural Sciences and Engineering Research Council
(NSERC) and the Canada Council for the Arts
(CCA) to Stephen McAdams; and by the Centre
for Interdisciplinary Research in Music, Médias,
and Technology (CIRMMT). Thanks to Matthias
Geier, Sandra Duric, Finn Upham, and Catherine
Guastavino for discussions and suggestions during
the different phases of this research.

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Computer Music Journal

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