<commit_before>% -----------------------------------------------
% Template for SMC 2009
%     smc2009.sty -> style file
% Last modified by <NAME> (<EMAIL>)
% Modified by <NAME> (<EMAIL>)
% By <NAME> (<EMAIL>)
% Based on the 2004 template by <NAME>.
% -----------------------------------------------

\documentclass{article}
\usepackage{smc2009,amsmath}
% To use when using pdflatex
\usepackage{graphicx}
\usepackage{url}     
\usepackage{hyperref}   
      
\newenvironment{packed_item}{
\begin{itemize}
  \setlength{\itemsep}{1pt}
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% To use when using latex, dvips and ps2pdf
% \usepackage[dvips]{graphicx}

% Title.
% ------
%\title{a layered approach to sound spatialization - concepts and examples}
\title{A stratified approach for sound spatialization}
% IMPORTANT NOTICE:
% Reviews are double-blind
% Authors will not be informed of who reviews their papers, and author names will be concealed from the reviewers 
% Please avoid evident self references in the text

% Authors' names must be omitted from title page (or listed as name(s) omitted for submission)


% Single address
% To use with only one author or several with the same address
% ---------------
%\oneauthor
%   {Author} {School \\ Email}

% Two addresses
 %--------------
\twoauthors
  {First author} {School \\ Email}
  {Second author} {Company \\ Email}

% Three addresses
% --------------
%\threeauthors
%  {First author} {School \\ Email}
%  {Second author} {Company \\ Email}
%  {Third author} {Company \\ Email}


\begin{document}
%    
\sloppy
\maketitle
%

\permission

\begin{abstract}
The improvements in computer and audio equipment in recent years makes it possible to experiment more freely with resource-demanding sound synthesis techniques such as spatialization. For seeking new means of expression different spatialization applications should be easily combined and accessible for both programmatic and user interfaces. % and/or other controllers. %e.g. a generative mapping of a granular synth output to different spatial renderer from one common user interface, while also streaming spatial encoded audio to the internet. 
Guaranteeing efficient workflow for non-standardized approaches requires structure, flexibility, and interoperability. Common spatialization systems are too often self-contained giving no consideration to these requirements. Therefore, we propose a multi-layer approach to mediate sound spatialization to meet these demands.\\                              	
\textbf{Keywords:} sound spatialization, interoperability, layered architecture, adaptation, site-specific, Ambisonics , TODO: make better \& stronger keywords   
%-flexible working environment for spatialization\\
%-A layered approach towards interoperability in sound spatialization management\\
%The abstract should be placed at the top left column and should contain
%about 150-200 words.
%stratified     strata  stratum 
%KEYWORDS : 
\end{abstract}

\section{Introduction}\label{sec:introduction}       
The goal of any spatialization
%rendering is it only the rendering system, or control/rendering ?
system is to facilitate or empower the creative use of the spatial medium for a sonic artist. Quantitative studies on spatial music (\cite{otondo2008ctu}, \cite{PetersSurvey}) remind us that there are great individual and context-related differences in defining that goal amongst artists. %that the compositional use of spatialization techniques varies strongly across composers and musical context.    
The requirements of a computer aided spatialization system may vary between a fixed-media composition (e.g \cite{BarrettOS02}%TODO: find a <NAME> reference
), an art-installation (\cite{lossius:2007sound_space_body}), and a live diffusion performance (\cite{Truax99}). 
One example is an interactive art installation where the real-time quality of a spatial rendering system is of great importance in combination with the possibility to control spatial processes through a multi-touch screen.  Juxtaposed is a second example: a performance of a fixed-media composition where the paramount features may be multichannel playback and the compensation of non-equidistant loudspeakers (in terms of sound pressure and time delays). Additional scenarios may require binaural rendering for headphone listening, multichannel recording, up and down mixing, or a visual representation of a sound scene.  
Moreover, even during the creation of one spatial art work, the importance of these requirements may change throughout different stages of the creative processes. % \emph{Experimentation -- Arranging -- Performance -- Documentation}. 
%Several common paradigms for spatial sound synthesis are outlined in section \ref{sec:review}. %The availability of better CPU resources in recent years makes it possible to experiment more freely with these paradigms for seeking new ways of expressions, e.g. a generative mapping of a granular synth output to different spatial renderer from one common user interface, while also streaming spatial encoded audio to the internet. This paper shows how such complex spatialization scenarios can be conceptualized through a multi-layer structure.    



%\begin{packed_item} 
%	\item {real-time or non real-time rendering}  
%%	\item {Plug-In structure: exchangeable renderer and interface components} - this is one of the ideas of the article, we don't need it here
%	\item {multichannel playback and recording possibility} 	
%	\item {binaural rendering for headphone listening}
%	\item {testing technical setup, e.g. loudspeaker connections}   
%	\item {customizable renderer in order to accommodate for different acoustical conditions, e.g. adapting the virtual room description to the listening room} 
%\item {customizable to accommodate for different technical conditions, e.g. rendering to different reproduction formats, compensation for non-ideal loudspeaker configurations, routing signals to dedicated physical outputs}  
%	\item {visual representation of a sound scene} 
%\item {separate render and control layer} - this is one of the ideas of the article, we don't need it here
%\item {allowing for external control e.g. through MIDI, OSC or other protocols}
%
%\end{packed_item}
%TODO: this list must become better!-please help - \emph{what do we want to say with this list ??} \\

%The outlined requirements may differ according to artistic paradigms.
%-Use cases (users : composers, installation artists, scientists...etc...)
%   - OpenMusic off-line rendering
%   - BEAST sound diffusion (the more speaker - the mre complicated to perform)
%   - interactive sound installations
%   - real-time control via sensors/gestural controller etc. by performer
%   - tape-music (fixed media)
%   - computer generated - real time spatialization (see <meta-description> layer)
   
    
%Experimental stage:\\
%\begin{packed_item}
% \item {Plug-In structure: exchangeable renderer and interface components} 
% \item {multichannel recording possibility for capturing of sketches/ideas}         
% \item {present management}
% \item {sound scene visualization - especially for off-line rendering of spatial processes}
%\end{packed_item} 

%Compositional stage:\\  
%\begin{packed_item}
%  \item {binaural rendering for headphone listening} 
%\end{packed_item} 
%Performance stage:\\
%\begin{packed_item} 
%	\item {customizable to accommodate for different technical conditions, e.g. rendering to different reproduction formats, compensation for non-ideal %loudspeaker configurations, routing signals to dedicated physical outputs}   
%    \item {testing technical setup, e.g. loudspeaker connections}
%    \item {customizable to accommodate for different acoustical conditions, e.g. adapting the virtual room description to the listening room} 
%\end{packed_item} 
%Documentation stage:\\  
%\begin{packed_item}
%\item {multichannel recording possibility}         
%\item {storing }       
%\end{packed_item}  


%\quote{ What WE need, for our personal work, is a way to extend the capabilities of those tools in a completely flexible and configurable way - and that suggests plug-ins (though it will always be a potential problem overcoming inherent IO structures in the host applications).}

%\quote{working with non-standard loudspeakers: Meyer Sound Spherical Loudspeaker Array that is under research at CNMAT, or the Hemisphere Point-source Emanation Loudspeaker, for example.  I would like to experiment with these;}

%\quote{Tool building and music making happen together and depend upon each other.}

%\quote{Very frustrated with my current spatialization software and am desperately looking for something better!}

\section{Review of current Paradigms} \label{sec:review}
%This section gives an overview of current paradigms and solutions for sound spatialization, and shows their limitations. 
\subsection{Live sound diffusion}  
?? shall we mention live diffusion as a paradigm ?
\subsection{Digital Audio Workstations - DAW} \label{sec:digital audio workstations - DAW} 
Currently, many composers and sound-artists use DAWs for designing their sound spatialization primarily in the context of fixed media, tape-music, and consumer media production. Users of DAWs often have former experience with live diffusion systems, or with panning in a hardware mixing console. Their migration to DAWs seems reasonable because the linear time representation of sound material and the audio bus architecture in DAWs originates from the use of multitrack tape recorder and mixing consoles. 
A number of (mainly commercial) DAWs are mature and offer a systematic user interface, good project and sound file management, and extendability through plug-ins.  They can fulfill the needs of many users in the described context.\\
However, through focusing on consumer media products, multichannel capabilities are limited. ITU 5.1, a surround sound format with equidistant loudspeakers around an ideal located listener and originally designed for the requirements of the film industry, is the most common multichannel format in DAWs and in surround panning plugins. 
Moreover, the 5.1 setup favors frontal direction and has limited capabilities for localizing virtual sources from the sides and back, which may limit its artistic use.  More recently, extensions to 7.1 or 10.2 are available\footnote{A comparison of DAWs concerning their multichannel audio capabilities shows \url{http://acousmodules.free.fr/hosts.htm}.}.   
Non-commercial loudspeaker setups are used in art installations or concert hall environments varying in number and layout.  These configurations are not typically anticipated by existing DAW software. Consequently, existing DAW-projects are difficult to adapt to these situations. 
%From 1993, emergence of the ITU 5.1 has been announced as a major improvement for mixing surround sound. Originally designed to fulfill the needs of the film industry, this loudspeaker configuration appeared to music and entertainment companies as a new way to extend their commercial offer. Since then, all DAWs surround panners have been designed to respect and organize sound processing for this set-up. It was not until the late nineties that new suggestions for surround workstations (from 6.1 to 10.2, enhancing sides precision, and perception outside of the Central Listening Position) were considered.\\
%This was an useful approach for recording, multimedia or film prospects (cannot do business without standards), but still in a regular, circular, geometric and (FIXME: non-neutral ?we mean it influences the user) design, which cannot be acceptable and sufficient for creation or live applications. As an example, a non-flexible loudspeaker circle set-up is very rarely adapted to the concert hall.\\ 
\\Another critical function for surround sound mixing is the means by which a sound source's energy is distributed amongst the loudspeakers. A \emph{blur} parameter, which determines the apparent source width of a panned signal, should be a standard control element of every surround panner because it enables many variations and possibilities for a creative mix. %and because we would work with this parameter considering the specific features of the sound we have to spatialize. 
In most applications, this factor is restricted and linked to the sound source's position relative to the center in the surround panner, and is related to parameters such as \emph{spread} or \emph{diversity} (e.g. in Apple Logic Pro \footnote{\url{www.apple.com/logicstudio/}}). To the authors' opinion, the most flexible control element can be found in Sequoia \footnote{\url{http://www.magix.com/us/sequoia/}}, with \emph{soundfield} offset and character (shape) settings for each track, a \emph{global divergence} to fit to the listening room size, and a complete flexibility for the speaker set-up in the listening area. 
%
%
% Did we discuss all point below:? (moved above -> we should use them at the beginning IMHO)
%
%
%spatialization is mainly done in DAWs and leads to "panning" because the bus architectures and interfaces of the panning plugins suggests this.
%    Limitations:
%        a) mainly tied to consumer formats (stereo and ITU 5:1 surround)
%        b) restricted to linear prerendering compositional processes
%        c) complicated to maintain automation when changing rendering plugIn
%        d) burden to connect interfaces (Lemur, Stantum, Wacom, Camera-tracking)
%        
% 
      
\subsection{Media programming environments}  \label{sec:Media programming environments}
Beside the paradigm of the DAW, various media programming environments exist that are capable of spatial sound synthesis. These include SuperCollider, Pure Data, Chuck, OpenMusic, and Max/MSP.  In order to support individual approaches and to meet the specific needs of computer music and mixed media art, these environments enable the user to combine music making with computer programming.\\  
However, in the name of complete flexibility, these environments lack in providing structured solutions for the specific challenges of spatial music as outlined in section \ref{sec:introduction}. Consequently, numerous self-contained spatialization libraries and toolboxes have been created by artists and researchers to generate virtual sound sources and artificial spaces.  These include the Space Unit Generator \cite{SUG02}, IRCAM's Spatialisateur \cite{JotPhD}, and Virtual Microphone Control \cite{CMJ08-VIMIC}. Also toolboxes primarily dedicated to sound diffusion practice, such as the BEASTmulch System\footnote{\url{http://www.beast.bham.ac.uk/research}}, or ICAST \cite{ICAST06} are available.   
Each tool, however, may only provide solutions for a subset of compositional viewpoints.  The development of new aesthetics through combining these tools is difficult or limited through their specific designs. 

\section{Strategies \& Methodologies in sound spatialization}  
 
A traditional workflow in electroacoustic composition or linear sound editing comprises a number of steps leading to the construction of the audio scene. Other contexts such as audio installations or interactive/multimedia work imply a different sequence in the steps of the process. The modular approach tries to abstract these differences and define underlying common elements that are always in play when spatialization is used. This layer model doesn't imply a specific method, it much rather tries to emphasize the importance of the interchangeability of modules, which share their interconnecting interfaces. The tools for each layer can be exchanged and compared, without forcing the artist to completely rebuild their setup.

\begin{quote}Spatial orchestration eases this [...] constraint, [...] the composition may be reconfigured for each individual performance. This will require [...] the composer [to] conceive spatial attributes in a more abstract fashion, that is then instantiated in potentially different ways into different performance environments. \cite{Lyon:2008spatial_orchestration} \end{quote}
By working symbolically during the composition/editing process and separating the authoring from the rendering processes a realization can become portable. A common set of descriptors and shared representation metaphors such as timelines or scene graphs builds the glue to make a disparate set of tools into a coherent workflow by enhancing interoperability between the different building blocks.\\
Modularity is another essential tenet.  Modularity allows the separation of elements into different layers according to their function as described in \ref{sec:layers}.  Furthermore, Modularity provides a means by which   modules may query additional modules and then adapt themselves to other parts of the graph.\\
The Tools used for authoring or rendering must comply to these recommendations, and can be separated in two categories : rendering engines and authoring meta-tools.\\


\subsection{A layered approach to the spatialization workflow}\label{sec:layers}
%TROND, J45CH\\
In order to better grasp the structural and methodological entities used in a spatialization process, a layered approach is proposed, which defines the problem domains in an ascending order of abstraction (Table \ref{fig:layers}). This model gets its inspiration from the OSI network model \footnote{\url{http://en.wikipedia.org/wiki/OSI_model}}. OSI (Open Systems Interconnection), is an abstract description for layered communications and computer network protocol design, which divides network architecture into seven layers which range, from top to bottom, between the Application and the Physical Layers
%
%
%\begin{packed_enumerate}   
%\item[5.]{controlling the rendering (e.g. HoloEdit, ambicontrol, swarms, boids \cite{kimboyle:ssp}, trajectories...)     <indirect control %description or meta-description>
%       Protocol: SpatDIF extended }
%\item[4.]{position of sources and speakers at one moment in time as SpatDIF                          <direct control description>
%       Protocol: SpatDIF core, SpatDIF extended if required by the encoder }
%\item[3.]{encoded audio
%       Protocols:
%           Spatial infomation embedded in format: (e.g. B-format and Dirac, MPEG-surround ?)
%           SpatDIF core and extended if required by the encoder (concerning info on target system) }
%\item[2.]{decoded audio
%       Protocols: E.g. CoreAudio, Jack, PortAudio }
%\item[1.]{physical layer (computers, sound cards, speakers, etc.)}
%\end{packed_enumerate}  
%TODO: sketch of the layers?
%<commit_msg>Section 3: - I added a TODO for someone about the end of the first paragraph. - I worked on the following paragraphs.  They are still not very satisfying, but I'm getting tired.  Is everyone else happy with the structure of this section?<commit_after>% -----------------------------------------------
% Template for SMC 2009
%     smc2009.sty -> style file
% Last modified by <NAME> (<EMAIL>)
% Modified by <NAME> (<EMAIL>)
% By <NAME> (<EMAIL>)
% Based on the 2004 template by <NAME>.
% -----------------------------------------------

\documentclass{article}
\usepackage{smc2009,amsmath}
% To use when using pdflatex
\usepackage{graphicx}
\usepackage{url}     
\usepackage{hyperref}   
      
\newenvironment{packed_item}{
\begin{itemize}
  \setlength{\itemsep}{1pt}
  \setlength{\parskip}{0pt}
  \setlength{\parsep}{0pt}
}{\end{itemize}}

\newenvironment{packed_enumerate}{
\begin{enumerate}
  \setlength{\itemsep}{1pt}
  \setlength{\parskip}{0pt}
  \setlength{\parsep}{0pt}
}{\end{enumerate}}
% To use when using latex, dvips and ps2pdf
% \usepackage[dvips]{graphicx}

% Title.
% ------
%\title{a layered approach to sound spatialization - concepts and examples}
\title{A stratified approach for sound spatialization}
% IMPORTANT NOTICE:
% Reviews are double-blind
% Authors will not be informed of who reviews their papers, and author names will be concealed from the reviewers 
% Please avoid evident self references in the text

% Authors' names must be omitted from title page (or listed as name(s) omitted for submission)


% Single address
% To use with only one author or several with the same address
% ---------------
%\oneauthor
%   {Author} {School \\ Email}

% Two addresses
 %--------------
\twoauthors
  {First author} {School \\ Email}
  {Second author} {Company \\ Email}

% Three addresses
% --------------
%\threeauthors
%  {First author} {School \\ Email}
%  {Second author} {Company \\ Email}
%  {Third author} {Company \\ Email}


\begin{document}
%    
\sloppy
\maketitle
%

\permission

\begin{abstract}
The improvements in computer and audio equipment in recent years makes it possible to experiment more freely with resource-demanding sound synthesis techniques such as spatialization. For seeking new means of expression different spatialization applications should be easily combined and accessible for both programmatic and user interfaces. % and/or other controllers. %e.g. a generative mapping of a granular synth output to different spatial renderer from one common user interface, while also streaming spatial encoded audio to the internet. 
Guaranteeing efficient workflow for non-standardized approaches requires structure, flexibility, and interoperability. Common spatialization systems are too often self-contained giving no consideration to these requirements. Therefore, we propose a multi-layer approach to mediate sound spatialization to meet these demands.\\                              	
\textbf{Keywords:} sound spatialization, interoperability, layered architecture, adaptation, site-specific, Ambisonics , TODO: make better \& stronger keywords   
%-flexible working environment for spatialization\\
%-A layered approach towards interoperability in sound spatialization management\\
%The abstract should be placed at the top left column and should contain
%about 150-200 words.
%stratified     strata  stratum 
%KEYWORDS : 
\end{abstract}

\section{Introduction}\label{sec:introduction}       
The goal of any spatialization
%rendering is it only the rendering system, or control/rendering ?
system is to facilitate or empower the creative use of the spatial medium for a sonic artist. Quantitative studies on spatial music (\cite{otondo2008ctu}, \cite{PetersSurvey}) remind us that there are great individual and context-related differences in defining that goal amongst artists. %that the compositional use of spatialization techniques varies strongly across composers and musical context.    
The requirements of a computer aided spatialization system may vary between a fixed-media composition (e.g \cite{BarrettOS02}%TODO: find a Robert Normandeau reference
), an art-installation (\cite{lossius:2007sound_space_body}), and a live diffusion performance (\cite{Truax99}). 
One example is an interactive art installation where the real-time quality of a spatial rendering system is of great importance in combination with the possibility to control spatial processes through a multi-touch screen.  Juxtaposed is a second example: a performance of a fixed-media composition where the paramount features may be multichannel playback and the compensation of non-equidistant loudspeakers (in terms of sound pressure and time delays). Additional scenarios may require binaural rendering for headphone listening, multichannel recording, up and down mixing, or a visual representation of a sound scene.  
Moreover, even during the creation of one spatial art work, the importance of these requirements may change throughout different stages of the creative processes. % \emph{Experimentation -- Arranging -- Performance -- Documentation}. 
%Several common paradigms for spatial sound synthesis are outlined in section \ref{sec:review}. %The availability of better CPU resources in recent years makes it possible to experiment more freely with these paradigms for seeking new ways of expressions, e.g. a generative mapping of a granular synth output to different spatial renderer from one common user interface, while also streaming spatial encoded audio to the internet. This paper shows how such complex spatialization scenarios can be conceptualized through a multi-layer structure.    



%\begin{packed_item} 
%	\item {real-time or non real-time rendering}  
%%	\item {Plug-In structure: exchangeable renderer and interface components} - this is one of the ideas of the article, we don't need it here
%	\item {multichannel playback and recording possibility} 	
%	\item {binaural rendering for headphone listening}
%	\item {testing technical setup, e.g. loudspeaker connections}   
%	\item {customizable renderer in order to accommodate for different acoustical conditions, e.g. adapting the virtual room description to the listening room} 
%\item {customizable to accommodate for different technical conditions, e.g. rendering to different reproduction formats, compensation for non-ideal loudspeaker configurations, routing signals to dedicated physical outputs}  
%	\item {visual representation of a sound scene} 
%\item {separate render and control layer} - this is one of the ideas of the article, we don't need it here
%\item {allowing for external control e.g. through MIDI, OSC or other protocols}
%
%\end{packed_item}
%TODO: this list must become better!-please help - \emph{what do we want to say with this list ??} \\

%The outlined requirements may differ according to artistic paradigms.
%-Use cases (users : composers, installation artists, scientists...etc...)
%   - OpenMusic off-line rendering
%   - BEAST sound diffusion (the more speaker - the mre complicated to perform)
%   - interactive sound installations
%   - real-time control via sensors/gestural controller etc. by performer
%   - tape-music (fixed media)
%   - computer generated - real time spatialization (see <meta-description> layer)
   
    
%Experimental stage:\\
%\begin{packed_item}
% \item {Plug-In structure: exchangeable renderer and interface components} 
% \item {multichannel recording possibility for capturing of sketches/ideas}         
% \item {present management}
% \item {sound scene visualization - especially for off-line rendering of spatial processes}
%\end{packed_item} 

%Compositional stage:\\  
%\begin{packed_item}
%  \item {binaural rendering for headphone listening} 
%\end{packed_item} 
%Performance stage:\\
%\begin{packed_item} 
%	\item {customizable to accommodate for different technical conditions, e.g. rendering to different reproduction formats, compensation for non-ideal %loudspeaker configurations, routing signals to dedicated physical outputs}   
%    \item {testing technical setup, e.g. loudspeaker connections}
%    \item {customizable to accommodate for different acoustical conditions, e.g. adapting the virtual room description to the listening room} 
%\end{packed_item} 
%Documentation stage:\\  
%\begin{packed_item}
%\item {multichannel recording possibility}         
%\item {storing }       
%\end{packed_item}  


%\quote{ What WE need, for our personal work, is a way to extend the capabilities of those tools in a completely flexible and configurable way - and that suggests plug-ins (though it will always be a potential problem overcoming inherent IO structures in the host applications).}

%\quote{working with non-standard loudspeakers: Meyer Sound Spherical Loudspeaker Array that is under research at CNMAT, or the Hemisphere Point-source Emanation Loudspeaker, for example.  I would like to experiment with these;}

%\quote{Tool building and music making happen together and depend upon each other.}

%\quote{Very frustrated with my current spatialization software and am desperately looking for something better!}

\section{Review of current Paradigms} \label{sec:review}
%This section gives an overview of current paradigms and solutions for sound spatialization, and shows their limitations. 
\subsection{Live sound diffusion}  
?? shall we mention live diffusion as a paradigm ?
\subsection{Digital Audio Workstations - DAW} \label{sec:digital audio workstations - DAW} 
Currently, many composers and sound-artists use DAWs for designing their sound spatialization primarily in the context of fixed media, tape-music, and consumer media production. Users of DAWs often have former experience with live diffusion systems, or with panning in a hardware mixing console. Their migration to DAWs seems reasonable because the linear time representation of sound material and the audio bus architecture in DAWs originates from the use of multitrack tape recorder and mixing consoles. 
A number of (mainly commercial) DAWs are mature and offer a systematic user interface, good project and sound file management, and extendability through plug-ins.  They can fulfill the needs of many users in the described context.\\
However, through focusing on consumer media products, multichannel capabilities are limited. ITU 5.1, a surround sound format with equidistant loudspeakers around an ideal located listener and originally designed for the requirements of the film industry, is the most common multichannel format in DAWs and in surround panning plugins. 
Moreover, the 5.1 setup favors frontal direction and has limited capabilities for localizing virtual sources from the sides and back, which may limit its artistic use.  More recently, extensions to 7.1 or 10.2 are available\footnote{A comparison of DAWs concerning their multichannel audio capabilities shows \url{http://acousmodules.free.fr/hosts.htm}.}.   
Non-commercial loudspeaker setups are used in art installations or concert hall environments varying in number and layout.  These configurations are not typically anticipated by existing DAW software. Consequently, existing DAW-projects are difficult to adapt to these situations. 
%From 1993, emergence of the ITU 5.1 has been announced as a major improvement for mixing surround sound. Originally designed to fulfill the needs of the film industry, this loudspeaker configuration appeared to music and entertainment companies as a new way to extend their commercial offer. Since then, all DAWs surround panners have been designed to respect and organize sound processing for this set-up. It was not until the late nineties that new suggestions for surround workstations (from 6.1 to 10.2, enhancing sides precision, and perception outside of the Central Listening Position) were considered.\\
%This was an useful approach for recording, multimedia or film prospects (cannot do business without standards), but still in a regular, circular, geometric and (FIXME: non-neutral ?we mean it influences the user) design, which cannot be acceptable and sufficient for creation or live applications. As an example, a non-flexible loudspeaker circle set-up is very rarely adapted to the concert hall.\\ 
\\Another critical function for surround sound mixing is the means by which a sound source's energy is distributed amongst the loudspeakers. A \emph{blur} parameter, which determines the apparent source width of a panned signal, should be a standard control element of every surround panner because it enables many variations and possibilities for a creative mix. %and because we would work with this parameter considering the specific features of the sound we have to spatialize. 
In most applications, this factor is restricted and linked to the sound source's position relative to the center in the surround panner, and is related to parameters such as \emph{spread} or \emph{diversity} (e.g. in Apple Logic Pro \footnote{\url{www.apple.com/logicstudio/}}). To the authors' opinion, the most flexible control element can be found in Sequoia \footnote{\url{http://www.magix.com/us/sequoia/}}, with \emph{soundfield} offset and character (shape) settings for each track, a \emph{global divergence} to fit to the listening room size, and a complete flexibility for the speaker set-up in the listening area. 
%
%
% Did we discuss all point below:? (moved above -> we should use them at the beginning IMHO)
%
%
%spatialization is mainly done in DAWs and leads to "panning" because the bus architectures and interfaces of the panning plugins suggests this.
%    Limitations:
%        a) mainly tied to consumer formats (stereo and ITU 5:1 surround)
%        b) restricted to linear prerendering compositional processes
%        c) complicated to maintain automation when changing rendering plugIn
%        d) burden to connect interfaces (Lemur, Stantum, Wacom, Camera-tracking)
%        
% 
      
\subsection{Media programming environments}  \label{sec:Media programming environments}
Beside the paradigm of the DAW, various media programming environments exist that are capable of spatial sound synthesis. These include SuperCollider, Pure Data, Chuck, OpenMusic, and Max/MSP.  In order to support individual approaches and to meet the specific needs of computer music and mixed media art, these environments enable the user to combine music making with computer programming.\\  
However, in the name of complete flexibility, these environments lack in providing structured solutions for the specific challenges of spatial music as outlined in section \ref{sec:introduction}. Consequently, numerous self-contained spatialization libraries and toolboxes have been created by artists and researchers to generate virtual sound sources and artificial spaces.  These include the Space Unit Generator \cite{SUG02}, IRCAM's Spatialisateur \cite{JotPhD}, and Virtual Microphone Control \cite{CMJ08-VIMIC}. Also toolboxes primarily dedicated to sound diffusion practice, such as the BEASTmulch System\footnote{\url{http://www.beast.bham.ac.uk/research}}, or ICAST \cite{ICAST06} are available.   
Each tool, however, may only provide solutions for a subset of compositional viewpoints.  The development of new aesthetics through combining these tools is difficult or limited through their specific designs. 

\section{Strategies \& Methodologies in sound spatialization}  
 
A traditional workflow in electroacoustic composition or linear sound editing comprises a number of steps leading to the construction of an audio scene. Other contexts, such as audio installations or interactive/multimedia work, imply a different sequence in the steps of the process. A layered modular approach tries to abstract these differences and define underlying common elements that are always in play when spatialization is used. This layered model doesn't imply a specific method.  It much rather emphasizes the importance of the interchangeability of modules, which share their interconnecting interfaces and communication protocol.  Thus, the tools for each layer can be exchanged and compared without forcing an artist to completely rebuild their setup.  TODO:  I (Tim) am not sure what word to use at the end of the preceding sentence, but you cannot use 'setup'.  Using 'setup' as a noun is not really correct English; when it is used it is considered extremely informal.

\begin{quote}Spatial orchestration eases this [...] constraint, [...] the composition may be reconfigured for each individual performance. This will require [...] the composer [to] conceive spatial attributes in a more abstract fashion that is then instantiated in potentially different ways into different performance environments. \cite{Lyon:2008spatial_orchestration} \end{quote}
By working symbolically during the composition/editing process, and separating the authoring from the rendering processes, a realization can become portable. A common set of descriptors and shared representation metaphors, such as timelines or scene graphs, builds the glue to make a disparate set of tools into a coherent workflow by enhancing interoperability between the building blocks.\\
Thus modularity is an essential tenet.  Modularity allows the separation of elements into different layers according to their function as described in \ref{sec:layers}.  Furthermore, Modularity provides a means by which modules may query additional modules and then adapt themselves to the system's topography.\\
The Tools used for authoring and rendering must comply to these recommendations and can be separated into two categories: rendering engines and authoring meta-tools.\\


\subsection{A layered approach to the spatialization workflow}\label{sec:layers}
%TROND, J45CH\\
In order to better grasp the structural and methodological entities used in a spatialization process, a layered approach is proposed, which defines the problem domains in an ascending order of abstraction (Table \ref{fig:layers}). This model gets its inspiration from the OSI network model \footnote{\url{http://en.wikipedia.org/wiki/OSI_model}}. OSI (Open Systems Interconnection), is an abstract description for layered communications and computer network protocol design, which divides network architecture into seven layers which range, from top to bottom, between the Application and the Physical Layers
%
%
%\begin{packed_enumerate}   
%\item[5.]{controlling the rendering (e.g. HoloEdit, ambicontrol, swarms, boids \cite{kimboyle:ssp}, trajectories...)     <indirect control %description or meta-description>
%       Protocol: SpatDIF extended }
%\item[4.]{position of sources and speakers at one moment in time as SpatDIF                          <direct control description>
%       Protocol: SpatDIF core, SpatDIF extended if required by the encoder }
%\item[3.]{encoded audio
%       Protocols:
%           Spatial infomation embedded in format: (e.g. B-format and Dirac, MPEG-surround ?)
%           SpatDIF core and extended if required by the encoder (concerning info on target system) }
%\item[2.]{decoded audio
%       Protocols: E.g. CoreAudio, Jack, PortAudio }
%\item[1.]{physical layer (computers, sound cards, speakers, etc.)}
%\end{packed_enumerate}  
%TODO: sketch of the layers?
%
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