A virtual model for simulation and design of architectures in MPEG-4 audio and multimedia context

Research in multimedia for consumer electronics is dominated by the problem of incredibly short times-to-market, that means fast complexity estimations and fast design of new architectures. On one side more and more sophisticated and flexible applications are rapidly developed, on the other side the exponential growth in IC computational power seems to be hardly capable to keep pace with requirements for real-time applications, since their complexity is exponentially growing as well. The processor's performance, often slowed down by bottlenecks in memories and buses, is further reduced by the time wasted in communication among the several application layers. From this problem comes the conception of integrated development frameworks for simulation and design. Tools for simulation and analysis of architectures have appeared from academic and industrial research laboratories above all in the last decade. Many of them are conceived to provide low-level exact simulation of the supported devices, at the price of heavy slowdowns in simulation times and huge sizes of traced data reports. Some others, in the last years, introduced some degrees of approximation in simulations, in order to speed up execution time and to increase the flexibility of the tools to support multi-processors. The resulting more or less abstract models are anyway not suitable to analyze real multimedia-oriented applications, where programs are usually available in some languages including dedicated libraries and meaningful results are only those measured in function of time. On another level, tools for hardware/software codesign or for block-based system design provide more useful results, but to be effective they must rely on rigid cores that may allow only a few degrees of reconfigurability; some very recent tools are conceived to design complex systems by modeling blocks through a high level description language. Conversely, the virtual model and related tool proposed in this dissertation have their roots in an approach to the analysis of complexity that aims to be, as far as possible, platform independent. The method is based on the concepts of abstract classes of operations and simulation in function of the performance time. The work described in this dissertation finds its application field in the world of multimedia, more precisely in multimedia-oriented Audio applications. Media applications are commonly programmed by imperative or object-oriented languages, which are composed by many different statements, operators and above all standard libraries. A careful profiling of typical applications permits to detect fundamental operations and functions and to define a virtual instruction set, grouping more or less similar operators and breaking functions into basic building blocks. The resulting virtual instruction set does not correspond to any actual one but it has as property to be easily mapped on a large number of existing ones. The simulation of an architecture requires then the availability of measures, benchmarks or estimations of at least one member of each abstract class. The number of classes, i.e. the complexity vector, can be adapted in length and detail to the needed degree of precision and to the available set of actual measures and/or benchmarks. The input to the simulation is described by a high-level standardized programming language, the new MPEG-4 Structured Audio Orchestra Language (SAOL); in principle, it may also be the case that the application does not need any translation, if it is already available in this format. Moreover, simulation through a high-level language permits to trace the behavior of the target architecture in function of the internal time of the application itself, result that is fundamental when the related workload is highly variable as in downloadable and/or interactive scenarios. In such cases complexity has always been considered a guess. The new virtual model for analyses of complexity led to two main practical results: the proposed method of simulation has been used to define complexity levels for Structured Audio in the MPEG-4 Standard, and consequently the platform independent analyzer has become the MPEG-4 reference software for MPEG-4 SA Conformance test. a virtual instruction set has been conceived that has permitted the implementation of an efficient Structured Audio decoder, SAINT, based on a virtual interpreted DSP core. The flexibility of the SAINT virtual DSP approach has permitted a fast porting of its execution engine on a superscalar VLIW DSP, making it one of the building blocks of the ThreeDSPACE system, a framework for advanced rendering of 3-D Audio scenes based on MPEG-4 descriptions. The complete tool for simulation of architectures, including a cache simulator, has shown promising results, achieving estimations of the execution time of SAINT with an approximation of the 10% in the mean for a general purpose processor, and of the 20% for a very complex superscalar VLIW processor. Estimated programs have sometimes dynamic excursions of a factor 10 in their complexity along the time axis. In general, the experimental results can be considered in line with those of the most recent, state-of-the-art simulators presented in literature. A limitation of the language adopted to model the applications is that its generality is limited to onedimensional floating-point computation; the most relevant advantage is that simulation in function of the performance time is straightforward and provides the time-dependent results that are fundamental for the optimization of real-time applications. With the tool developed in this PhD work, complex programs can be quickly modeled thanks to SA specific libraries and also quickly analyzed; moreover, the tool can be easily extended to become a tool for automatic generation and configuration of the main building blocks of a system running the application, or the class of applications, under consideration. The proposed model is finally intended as an alternative approach to coordinate two sides; a principal goal of this work was to conceive and specify a systematic analysis method that can be useful to both the software programmer and to the hardware system engineer. The former can benefit of a reconfigurable and dedicated highlevel software tool able to profile programs in a simple and platform independent manner and to easily simulate, with some margins of error, the behavior of a specific platform, existing or virtual; the latter can exploit complexity estimations in an abstract format, with the possibility to study the target application in its several aspects (operations, memory usage, data flows among the different program blocks) and the potentiality to extend these results to an automatic generation of high-level system architectures

Parametrization, auralization, and authoring of room acoustics for virtual reality applications

The primary goal of this work has been to develop means to represent acoustic properties of an environment with a set of spatial sound related parameters. These parameters are used for creating virtual environments, where the sounds are expected to be perceived by the user as if they were listened to in a corresponding real space. The virtual world may consist of both visual and audio components. Ideally in such an application, the sound and the visual parts of the virtual scene are in coherence with each other, which should improve the user immersion in the virtual environment. The second aim was to verify the feasibility of the created sound environment parameter set in practice. A virtual acoustic modeling system was implemented, where any spatial sound scene, defined by using the developed parameters, can be rendered audible in real time. In other words the user can listen to the auralized sound according to the defined sound scene parameters. Thirdly, the authoring of creating such parametric sound scene representations was addressed. In this authoring framework, sound scenes and an associated visual scene can be created to be further encoded and transmitted in real time to a remotely located renderer. The visual scene counterpart was created as a part of the multimedia scene acting simultaneously as a user interface for renderer-side interaction.reviewe

Bimodal Audiovisual Perception in Interactive Application Systems of Moderate Complexity

The dissertation at hand deals with aspects of quality perception of interactive audiovisual application systems of moderate complexity as e.g. defined in the MPEG-4 standard. Because in these systems the available computing power is limited, it is decisive to know which factors influence the perceived quality. Only then can the available computing power be distributed in the most effective and efficient way for the simulation and display of audiovisual 3D scenes. Whereas quality factors for the unimodal auditory and visual stimuli are well known and respective models of perception have been successfully devised based on this knowledge, this is not true for bimodal audiovisual perception. For the latter, it is only known that some kind of interdependency between auditory and visual perception does exist. The exact mechanisms of human audiovisual perception have not been described. It is assumed that interaction with an application or scene has a major influence upon the perceived overall quality. The goal of this work was to devise a system capable of performing subjective audiovisual assessments in the given context in a largely automated way. By applying the system, first evidence regarding audiovisual interdependency and influence of interaction upon perception should be collected. Therefore this work was composed of three fields of activities: the creation of a test bench based on the available but (regarding the audio functionality) somewhat restricted MPEG-4 player, the preoccupation with methods and framework requirements that ensure comparability and reproducibility of audiovisual assessments and results, and the performance of a series of coordinated experiments including the analysis and interpretation of the collected data. An object-based modular audio rendering engine was co-designed and -implemented which allows to perform simple room-acoustic simulations based on the MPEG-4 scene description paradigm in real-time. Apart from the MPEG-4 player, the test bench consists of a haptic Input Device used by test subjects to enter their quality ratings and a logging tool that allows to journalize all relevant events during an assessment session. The collected data can be exported comfortably for further analysis using appropriate statistic tools. A thorough analysis of the well established test methods and recommendations for unimodal subjective assessments was performed to find out whether a transfer to the audiovisual bimodal case is easily possible. It became evident that - due to the limited knowledge about the underlying perceptual processes - a novel categorization of experiments according to their goals could be helpful to organize the research in the field. Furthermore, a number of influencing factors could be identified that exercise control over bimodal perception in the given context. By performing the perceptual experiments using the devised system, its functionality and ease of use was verified. Apart from that, some first indications for the role of interaction in perceived overall quality have been collected: interaction in the auditory modality reduces a human's ability of correctly rating the audio quality, whereas visually based (cross-modal) interaction does not necessarily generate this effect.Die vorliegende Dissertation beschäftigt sich mit Aspekten der Qualitätswahrnehmung von interaktiven audiovisuellen Anwendungssystemen moderater Komplexität, wie sie z.B. durch den MPEG-4 Standard definiert sind. Die Frage, welche Faktoren Einfluss auf die wahrgenommene Qualität von audiovisuellen Anwendungssystemen haben ist entscheidend dafür, wie die nur begrenzt zur Verfügung stehende Rechenleistung für die Echtzeit-Simulation von 3D Szenen und deren Darbietung sinnvoll verteilt werden soll. Während Qualitätsfaktoren für unimodale auditive als auch visuelle Stimuli seit langem bekannt sind und entsprechende Modelle existieren, müssen diese für die bimodale audiovisuelle Wahrnehmung noch hergeleitet werden. Dabei ist bekannt, dass eine Wechselwirkung zwischen auditiver und visueller Qualität besteht, nicht jedoch, wie die Mechanismen menschlicher audiovisueller Wahrnehmung genau arbeiten. Es wird auch angenommen, dass der Faktor Interaktion einen wesentlichen Einfluss auf wahrgenommene Qualität hat. Das Ziel dieser Arbeit war, ein System für die zeitsparende und weitgehend automatisierte Durchführung von subjektiven audiovisuellen Wahrnehmungstests im gegebenen Kontext zu erstellen und es für einige exemplarische Experimente einzusetzen, welche erste Aussagen über audiovisuelleWechselwirkungen und den Einfluss von Interaktion auf die Wahrnehmung erlauben sollten. Demzufolge gliederte sich die Arbeit in drei Aufgabenbereiche: die Erstellung eines geeigneten Testsystems auf der Grundlage eines vorhandenen, jedoch in seiner Audiofunktionalität noch eingeschränkten MPEG-4 Players, das Sicherstellen von Vergleichbarkeit und Wiederholbarkeit von audiovisuellen Wahrnehmungstests durch definierte Testmethoden und -bedingungen, und die eigentliche Durchführung der aufeinander abgestimmten Experimente mit anschlieÿender Auswertung und Interpretation der gewonnenen Daten. Dazu wurde eine objektbasierte, modulare Audio-Engine mitentworfen und -implementiert, welche basierend auf den Möglichkeiten der MPEG-4 Szenenbeschreibung alle Fähigkeiten zur Echtzeitberechnung von Raumakustik bietet. Innerhalb des entwickelten Testsystems kommuniziert der MPEG-4 Player mit einem hardwaregestützten Benutzerinterface zur Eingabe der Qualitätsbewertungen durch die Testpersonen. Sämtliche relevanten Ereignisse, die während einer Testsession auftreten, können mit Hilfe eines Logging-Tools aufgezeichnet und für die weitere Datenanalyse mit Statistikprogrammen exportiert werden. Eine Analyse der existierenden Testmethoden und -empfehlungen für unimodale Wahrnehmungstests sollte zeigen, ob deren Übertragung auf den audiovisuellen Fall möglich ist. Dabei wurde deutlich, dass bedingt durch die fehlende Kenntnis der zugrundeliegenden Wahrnehmungsprozesse zunächst eine Unterteilung nach den Zielen der durchgeführten Experimente sinnvoll erscheint. Weiterhin konnten Einflussfaktoren identifiziert werden, die die bimodale Wahrnehmung im gegebenen Kontext steuern. Bei der Durchführung der Wahrnehmungsexperimente wurde die Funktionsfähigkeit des erstellten Testsystems verifiziert. Darüber hinaus ergaben sich erste Anhaltspunkte für den Einfluss von Interaktion auf die wahrgenommene Gesamtqualität: Interaktion in der auditiven Modalität verringert die Fähigkeit, Audioqualität korrekt beurteilen zu können, während visuell gestützte Interaktion (cross-modal) diesen Effekt nicht zwingend generiert

Platforms for handling and development of audiovisual data

Estágio realizado na MOG Solutions e orientado por Vítor TeixeiraTese de mestrado integrado. Engenharia Informátca e Computação. Faculdade de Engenharia. Universidade do Porto. 200