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#18.ART • 2018 • ISSN: 2238-0272
17th to 19th of oct 2019
ANAIS
18º Encontro internacional de Arte, Ciência Tecnologia
18th International Meeting of Art, Science and Technology
18º Encontro internacional de Arte, Ciência Tecnologia
18th International Meeting of Art, Science and Technology
Edição I Edition
ISSN: 2238-0272
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Iain Mott1 and Thibaud Keller2
Three-dimensional sound design with Mosca
Spatialisation tri-dimensionnel avec Mosca
Abstract
Mosca is a software extension class of the SuperCollider language for sound
synthesis and algorithmic composition. It produces three-dimensional sound
elds via an intuitive graphical user interface controlling a variety of hidden
internal methods. Drawing from ambisonics’ adaptable form of surround
sound applicable to wide-ranging loudspeaker congurations and head-
phones, Mosca is suitable in a variety of applications. Recent improvements to
the software include the incorporation of high-order ambisonics and the OS-
SIA/score project, enabling sophisticated control of audio spatialisation and
synchronisation with a variety of media. Additionally, current development
will bring location sensitivity to Mosca. Together with existing head-tracking
capacities for binaural audio reproduction, the software will be highly useful
in mixed and virtual reality projects.
Keywords: ambisonics, surround sound, electroacoustic music, SuperCollider,
OSSIA/score
Résumé
Mosca est une extension pour l’environnement de programmation audio SuperCol-
lider. Cette extension permet la production de champs sonores tridimensionnels à
travers une interface graphique intuitive et diérentes méthodes internes. Tirant
prot de la exibilité du format ambisonique, compatible avec le rendu au casque
et une large gamme de congurations d’enceintes, Mosca peut s’adapter à un grand
nombre d’applications. Ce programme est actuellement développé par les auteurs
pour intégrer des ordres ambisoniques supérieurs, et davantage de techniques de
1 Sound artist, composer and lecturer in sound design and voice at the Departamento de Artes
Cênicas, Instituto de Artes, Universidade de Brasília, http://cen.unb.br. Doctorate in arts from the
University of Wollongong entitled “Sound Installation and Self-listening”. Personal website: https://
escuta.org. Institutional email: iainmott@unb.br.
2 Software technician and system administrator at SCRIME, University of Bordeaux, https://scrime.u-
-bordeaux.fr. Member of the OSSIA team, https://ossia.io. Masters in computer music programming
from the university of Saint-Etienne, https://musinf.univ-st-etienne.fr/index.html. Personal page: ht-
tps://github.com/thibaudk. Organisation page: https://github.com/scrime-u-bordeaux. Institutional
email: thibaud.keller@u-bordeaux.fr.
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spatialisation, ainsi que le projet OSSIA/score, permettant un contrôle sophistiqué
et la synchronisation, avec diérents médias. En outre, les développements actuels
apporteront à Mosca une localisation GPS de l’auditeur. Avec les possibilités actu-
elles de suivi du mouvement de la tête pour le rendu binaural, le programme pourra
facilement être utilisé pour des projets de réalité virtuelle et mixte.
Mots clefs: ambisoniques, spatialisation, musique électroacoustique, SuperCollider,
OSSIA/score
Introduction
Mosca is a software extension class (or quark) of the SuperCollider language for
sound synthesis and algorithmic composition, and was initially developed as part
of a research project entitled Cerrado Ambisônico by Iain Mott, assisted by the MCTI/
CNPq in the Edital Universal. The software produces surround sound and oers an
intuitive graphical user interface (GUI) for direct control. A variety of ambisonic and
spatial audio techniques are used to render three dimensional sound designs on
both headphones and wide-ranging loudspeaker congurations. Mosca makes ex-
tensive use of the the Ambisonic Toolkit (ATK) code library for ambisonic processing
and the Automation quark to sequence control data. Recent work by Thibaud Keller
has brought improvements to the GUI and seen the inclusion of additional spatial
audio libraries. Furthermore, communication with the multimedia sequencer OSSIA/
score is now enabled, facilitating live performances and synchronisation with other
real-time multimedia systems. Current work also includes location sensitivity via GPS
and accelerometers, derived from Mott’s sound mapping installation Botanica, pre-
sented in the proceedings of #16.Art.
As an extension of SuperCollider, Mosca is open source and runs on Linux, Mac and
Windows platforms. This article describes both current capabilities of Mosca and the
work in progress. Along with the documentation for the Mosca quark in SuperCol-
lider, this article serves as a practical guide to the software and provides the reader
with information to realise their own projects.
Ambisonic sound
Sound is not a static object. It is liberated from a source and propagated through
space by way of compression and rarefaction of air molecules. On a mild day of
20 degrees centigrade, it moves in waves through the air at the speed of approxi-
mately 343 metres per second. Various sounds arrive at our ears from all directions,
either directly or after having rst come into contact with surrounding objects and
materials. Ambisonics aims to both capture or synthesise and reproduce such
multidirectional sound elds for a certain region in space. Developed by Michael
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Gerzon and others in the UK and the USA in the early 1970s 3, ambisonics involves
encoding and decoding steps. To encode ambisonics is to process a sound source
or sources, for example a solo musical instrument or a ock of birds, by capturing
the waveform’s inherent phase and level information over a number of channels
and along specic spatial axes. Encoding may be done synthetically, by way of
digital or analogue processing, or acoustically, using a so-called soundeld4 mi-
crophone (Fellgett, 1975) rst developed by Michael Gerzon and Peter Craven in
the 1970s (Batke, 2009) with a number of capsules to capture the incoming sound
from multiple angles at once. As a convention, sound elds are generally encod-
ed in the multichannel B-format, which may exist at dierent spatial resolutions,
or ambisonic orders (Hollerweger, 2008) and is independent of the loudspeaker
conguration used for reproduction. The rendering of an ambisonic sound eld
is performed in the decoding step, where the signal is processed for a specic
loudspeaker array, whether it be a 2-dimensional arrangement of loudspeakers
surrounding an audience, or a three-dimensional array of loudspeakers and even
headphones, delivering a full spherical sonic experience.
Sound Sources
Mosca takes a exible approach to encoding and decoding. Sound sources may
be any combination of mono, stereo or B-format material and the signals may
originate from le (loaded into memory or streamed from disc), from hardware
inputs (physical or from other applications like a DAW via the Jack Audio Connec-
tion Kit (Jack)5) or from sound synthesis processes inside SuperCollider itself (Mc-
Cartney, 1996; Wilson, Cottle, & Collins, 2011). A particular source is rst selected
by right-clicking in a blank section in the GUI (Figure 1), then selecting its index
from the drop-down menu, with the total number of sources dened when initial-
ising Mosca. Once a source is selected, it can be assigned an input and the dened
sources appear as numbered circles in the GUI. The centre of the larger blue circle
denes the location of the listener or audience and its periphery marks the max-
imum audible distance from the listening point. Sources may be positioned and
moved in space by clicking and dragging.
3 For information on the origins and nature of ambisonics and extensive lists of early publications
on the subject, see: www.michaelgerzonphotos.org.uk. Ambisonics is under ongoing development
and many of the leading researchers participate in the email discussion group “Sursound”: https://
mail.music.vt.edu/mailman/listinfo/sursound. The website http://www.ambisonic.net alsoprovides
resources and the Wikipedia page on ambisonics provides an excellent technical introduction: ht-
tps://en.wikipedia.org/wiki/Ambisonics.
4 For information about encoding conventions see: https://www.ambisonic.net/leformats.html
5 http://jackaudio.org
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Figure 1. Typical Mosca work session
In order to spatialise the sound sources, mono and stereo inputs are processed
on a per-source basis by a selection of algorithm set from the “Library” pull-down
menu in the GUI. Users may choose between the ATK6, HOALib7 (Guillot, Paris, &
Deneu, n.d.), Ambitools (Grond & Lecomte, 2017)8, ADT(Heller & Benjamin, 2014)9,
BF-FMH, Josh and VBAP libraries10. The ATK and Josh are both restricted to 1st or-
der ambisonics, BF-FMH can either encode in 1st or 2nd order whereas Ambitools,
HOALib and ADTB oer up to 5th order ambisonics. The default ambisonic order of
Mosca is 1, however the user may enter a maximum order as an instantiation argu-
ment to perform higher order encoding and decoding. Josh is a simple ambisonic
granulator eect. VBAP on the other hand is a non-ambisonic method of sound
spatialisation unaected by the “maxorder” argument. The acronym stands for
vector based amplitude panning (Pulkki, 1997) and involves the panning of sound
sources between adjacent loudspeakers in an array, the details of which—angular
6 http://www.ambisonictoolkit.net
7 http://hoalibrary.mshparisnord.fr/en
8 https://github.com/sekisushai/ambitools
9 https://bitbucket.org/ambidecodertoolbox/adt
10 The last three libraries are provided by the ocial supercollider plugin repository
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location and distance—must be passed to Mosca in the creation arguments for
the Mosca instance. Regardless of the chosen technique for a particular source,
stereo signals are treated as two distinct mono signals, separated spatially by an
adjustable angle parameter.
B-format signals up to 5th order, when used as input to Mosca, have no need to
undergo ambisonic encoding. The signal can be oriented and transformed directly
in various ways. The user can load or stream existing archival B-format material or
create their own audio les, either by using Mosca itself to record B-format les from
manipulated sources (mono, stereo or B-format) or record their own material acous-
tically with a sound eld microphone. Most commonly available soundeld micro-
phones are so-called A-format devices. Recorded signals using these microphones
will therefore need to be processed into B-format for use. The original Mosca project
has made use of such a microphone, the Core Sound Tetramic along with a TASCAM
DR-680 digital recorder and B-format material has been generated from raw record-
ings using the Linux software Tetraproc (Adriaensen, 2007). The methodology used
and a sample processing script are available online.11
Mosca uses two techniques for positioning B-format sources in space. Either the
push transformation from the ATK library or the Beam formation techniques avail-
able in Ambitools (Lecomte, Gauthier, Langrenne, Berry, & Garcia, 2016). Both eects
diminish as the source approaches the centre point, surrounding the listener and
allowing the inherent ambisonic coding of the original signal to dominate. With the
ATK, this signal can also be gradually striped of its directional attributes with the “Di-
rectivity” control. Fully rolled back, this parameter renders B-format inputs as omni-
directional signals with constituent sounds surrounding the listening point equally
from all directions. Additionally, rotation of incoming ambisonic sound elds around
their Z-axis can be performed with the “Rotation” parameter.
Mono and stereo sources are fully contracted by default, setting a focused position
in space. When fully de-contracted with the contraction control in the GUI, the signal
becomes omnidirectional. B-format sources, on the other hand, are de-contracted
by default and contraction causes them to become spatially focussed. The parame-
ter thus oers continuous control over the source’s width, from a narrow point to an
enveloping mass. When mono or stereo signals are de-contracted, the spread and
diuse GUI options of the ATK library oer two dierent types of spectral smearing
over the spherical ambisonic image. Both have distinct rendering qualities and users
may nd that one suits a specic class of sounds better than the other, as is the case
with all available libraries.
11 http://escuta.org/en/proj/research/ambiresources/item/222-shell-script.html
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Distance and reverberation
Along with angular location, Mosca’s source signals are attenuated proportionally
to their distance from the origin, inside an audible radius of one-hundred metres. In
this way, as sources move from the centre of the GUI towards the periphery, they be-
come quieter before being silenced once outside the large blue circle. All sources are
subject to high-frequency attenuation with distance. Additionally, a proximity eect12
is available via the ATK as well as a near eld compensation13 through Ambitools.
Reverberation plays an important psychoacoustic role in the perceived distance of
a sounding object. Typically, as a sound approaches, the ratio of direct to reected
sound—for example from walls, oor and ceiling—increases. In other words, distant
sounds generally appear more reverberant than close sounds. Mosca provides two
reverberation controls, close and distant, each with a selectable reverberation types.
Along with the Freeverb14 and a plain all-pass option, convolution reverberation can be
used to accurately simulate the resonance of natural environments. The Mosca project
has created B-format tail room impulse responses (RIR) to that eect using Linux based
software written by Fons Adriaensen (2007). The methods used have been document-
ed online. 15 Banks of such RIRs may be passed to Mosca as initiation arguments.
The implementation of convolution reverberation, under the close control, can be
described as a 2nd order diuse A-format reverberation. This technique produces re-
verberation weighted in the direction of sound events encoded in the dry ambisonic
signal and involves conversion to and from A-format in order to apply the eect. The
encoded 2nd order ambisonic signal is converted to a 12-channel A-format signal
and convolved with a B-format RIR which has been upsampled to 2nd order and con-
verted to A-format impulse spectrum, a process that is performed automatically on
rst initialisation. A nal step converts this reverberated A-format signal back to 2nd
order B-format for decoding and audition (Anderson, 2011).
Presently in Mosca, the distant reverberation control attenuates a type of reverberation
described by John Chowning as local, whereby the return signal from the reverberation
process16 is mixed back with the source signal before the spatialisation phase, producing
a tightly spatially focused reverberant signal at the same angular location as the source.
Conversely in our implementation, the close reverberation control attenuates what
12 http://doc.sccode.org/Classes/FoaProximity.html
13 http://www.sekisushai.net/ambitools/hoa_encoder
14 https://ccrma.stanford.edu/~jos/pasp/Freeverb.html
15 http://escuta.org/en/proj/research/ambiresources/item/222-shell-script.html
16 In the case of Mosca, fed by the w component of the source’s B-format encoded signal.
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Chowning described as global reverberation, a type of reverberation that envelopes
the listener, albeit, in our implementation, with a source-directed weighting. The overall
eect is that as the source recedes from the listener, and as it moves from close to dis-
tant control, the width of the reverberant eld narrows (Chowning, 1977). In the future,
Mosca will also oer the option of applying A-format convolution reverberation under
distant as well as close control.
Movement, control and automation
Mosca is well disposed to create sound elds with moving sound sources and its
name was inspired in part by ambisonic recordings of ies—moscas in Portuguese—
made inadvertently during eld recordings in the national park of Chapada dos Vea-
deiros 17. It is also a reference to Trevor Wishart’s recordings of bluebottle ies for his
electroacoustic composition Red Bird. After attempts of recording a y axed to a
substrate, he discovered that only with a y in motion—achieved by waving a blue-
bottle attached to a stick in a stereo eld—“could the aural image ‘y’ be recreated”
(Wishart, 1996, p. 151). To reproduce this characteristic of moving sound, a scalable
Doppler eect is implemented in Mosca for each source.
Creating movements and animating parameters in Mosca can be done in a number
of ways. A quick and intuitive method relies on the Automation quark 18 and direct
interaction with the GUI. If users select record in the automation transport without
selecting play, any changes made with the interface—for instance loading particular
audio les, positioning sources, adjusting various level controls—are recorded as a
single register in memory and may be saved and later recalled as such, in a named
directory. If play is selected while recording, users may record the spatial movement
of sources and changes to the controls, as a continuous stream of data. The transport
may be rewound any number of times to overlay additional changes or to override
prior alterations of the controls. Again, the recorded data may be saved and later
reloaded from a named directory for playback. The transport may be synchronised
to a digital audio workstation (DAW) using Midi Machine Control (MMC) messages
by selecting the slave to MCC checkbox in the GUI 19. This allows Mosca to spatialise
multitrack audio compositions, the individual tracks being sent to Mosca via Jack to
individual sources with HW-in selected20.
17 B-format audio recordings from this eld work are available online on an interactive map: https://
escuta.org/mapa
18 https://github.com/neeels/Automation
19 This method has been tested to work with the open source DAW Ardour on Linux.
20 When selected in the GUI, the user must enter the number of channels and the starting bus number.
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Mosca can run without an active GUI by reading stored Automation data21 and may
also be controlled entirely through coded commands by way of proxies for the GUI
elements. Calling “myMoscaInstanceName.xboxProxy[i].value”, for example, will re-
turn the current x-coordinate of the source at index “i”. With the “valueAction” meth-
od, new values can be set in real time for any given parameter proxy. A full list of
available proxies is given in the help le for Mosca.
A major focus of Mosca’s rework was to enable communication with the intermedia se-
quencer OSSIA/score22 (Celerier, 2018). This open source project can be described as a
graphical language to formulate software interactions in time. The approach expands
on a traditional sequencer interface with the addition of exible durations, parallel
timelines, conditional branches and a host of communication protocols. Developed
as a virtual conductor, OSSIA/score allows the creation of scenarios where events and
processes obey “when”, “while” and “switch case” statements represented as Triggers,
Loops and Conditions. Open Sound Control (OSC) (Schmeder, Freed, & Wessel, 2010)
and OSCQuery23 compliant applications like Mosca can then be remotely controlled
and synchronised together inside a single scenario. Exposed on the network with the
OSSIA quark24 for supercollider, all of Mosca’s parameters appear within the device ex-
plorer of OSSIA/score. This new feature not only greatly improves the integration with
other systems, it also provides high level functionalities for editing large-scale spatial
audio compositions and real time interactive projects of all kinds.
Figure 2. OSSIA/score scenario example
21 Using initialisation arguments.
22 ossia.io
23 https://github.com/Vidvox/OSCQueryProposal
24 https://github.com/OSSIA/ossia-sclang
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Decoding
A variety of options are available for decoding, each dependent on the rendering
system used (binaural, 2D ring or 3D array). A SuperCollider decoder object, chosen
from a number of types, may be passed to the Mosca instance in an initialisation
argument. If none is provided, raw ambisonic components of the chosen order are
outputted for processing with an external decoder, such as Ambdec (Adriaensen,
2011). The AmbiDecoderToolbox library for Octave and Matlab (Heller & Benjamin,
2014) may also be used and is recommended for higher-order decoding. It enables
users to create custom decoders calibrated specically for their setup. The scripting
and compiling steps for ADT are described in the SC-HOA quark tutorials (Grond &
Lecomte, 2017). As mentioned, VBAP involves neither ambisonic encoding nor de-
coding, however Mosca does require VBAP to be initialised with an array of loud-
speaker coordinates (2D or 3D) passed as an initialisation argument.
When a binaural ambisonic decoder is used for headphone reproduction, it may be
advantageous to use a head-tracking device. In this way the sound eld rotates cor-
respondingly with rotations of the head and the listener may better audition each
source. Mosca provides support for the Arduino 9-Axes Motion Shield25 sensor with
the Arduino Uno26 microprocessor. The Mosca help le provides information on how
the head-tracker should be installed and congured. Movements of the head are
displayed in the GUI as values of heading, pitch and roll as well as corresponding ro-
tations of sound sources. These orientation controls, like the origin parameters, only
aect the relative spherical coordinates for every source, leaving the absolute Carte-
sian coordinates intact. Both types of coordinates are available in OSSIA/score when
exposed to the network.
Current work
Work is currently underway to bring location sensitivity to Mosca using SuperCol-
lider code developed in the sound art project Botanica (Mott, 2017). The code will
enable Mosca to import a map and then calibrate it to position a mobile listener in
accordance with their physical location. Longitude and latitude serial data may be
used as input, be it from GPS or from any location sensing device. The system de-
veloped uses a Ublox NEO-6M GPS module27 which is wired directly to the Arduino
Uno with 9-Axes Motion Shield. Coupled with head tracking, listeners will be able to
walk in a direction of their choice, or travel by some other means, to explore sound-
scapes spanning physical space. Together with existing head-tracking capacities for
25 https://store.arduino.cc/usa/9-axis-motion-shield
26 https://store.arduino.cc/usa/arduino-uno-rev3
27 https://lastminuteengineers.com/neo6m-gps-arduino-tutorial/
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binaural audio reproduction, location sensitivity will lend Mosca broad application
in mixed and virtual reality projects. The OSSIA quark is also under development to
take over from the now deprecated ossia-supercollider28 project, currently the only
way to enable OSCQuery communication. It will soon be recongured and based on
Pierre Cochard’s wsclang29 fork of SuperCollider and the changes then submitted to
the ocial SuperCollider repository.
Resources
The home page for Mosca is http://escuta.org/mosca. To use Mosca, SuperCollider
must be installed on a Linux, Mac or Windows computer along with SuperCollider’s
assortment of plugins, including HOA30 and the ATK31. Like SuperCollider and the
ATK, the Mosca source code and accompanying Arduino source for head-tracking,
are available on the Github site.32 As well as including the SuperCollider source code
for Mosca and help les, the repository, as mentioned above, contains the source
code for the Arduino-based head-tracker and should be loaded onto the device us-
ing the Arduino IDE33 software. The Mosca quark and additional prerequisite quarks
including the ATK may be loaded via the Quarks.gui interface in SuperCollider. Once
loaded, the user may access the Mosca help le and guide with full instructions and
code examples, by running the help command on the class name Mosca. Addition-
ally, the moscaproject.zip le contained within the git source may be used. Once
extracted, the archive contains the basic le structure for a Mosca project as well as
an example RIR le. A much larger project directory with B-format audio les is also
available on the site Escuta.org.34
Acknowledgements
Participation in this event was made possible with assistance from the Fundação de
Apoio a Pesquisa do Distrito Federal (FAP DF). The authors gratefully acknowledge
Joseph Anderson (ATK), Pierre Lecomte (Ambitools), Florian Grond (SC-HOA), Pierre
28 https://github.com/OSSIA/ossia-supercollider
29 https://github.com/pchdev/wsclang
30 https://github.com/scrime-u-bordeaux/sc3-pluginsHOA
31 http://www.ambisonictoolkit.net/download/supercollider
32 https://github.com/escuta/mosca
33 https://www.arduino.cc
34 http://escuta.org/tmp/moscaproject.zip. The archive includes a B-format audio recorded by Iain
Mott in Chapada dos Veadeiros and Brasilia as well as a Spitre recording by John Leonard, provided
with kind permission.
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Guillot (HoaLib), Neels Hofmeyr (Automation), Jean-Michël Celerier (OSSIA/score),
Pierre Cochard (ossia-supercollider & wsclang) and members of the SuperCollider
users and dev lists for their assistance and valuable suggestions.
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