Download Efficient Description and Rendering of Complex Interactive Acoustic Scenes Interactive environmental audio spatialization technology has become commonplace in personal computers and is migrating into portable entertainment platforms (including cell phones) and multiplayer game servers (virtual online worlds). While the primary current application of this technology is 3D game sound track rendering, it is ultimately necessary in the implementation of any personal or shared immersive virtual world (“virtual reality”). The successful development and deployment of such applications in new mobile or online platforms involves maximizing the plausibility of the synthetic 3D audio scene while minimizing the computational and memory footprint of the audio rendering engine. It also requires a flexible, standardized scene description model to facilate the development of applications targeting multiple platforms. This paper reviews a computationally efficient 3-D positional audio and spatial reverberation processing architecture for real-time virtual acoustics over headphones or loudspeakers, compatible with current interactive audio standards (including MPEG-4, OpenAL, JSR 234 and OpenSL ES).
Download 2nd Order Spherical Harmonic Spatial Encoding of Digital Waveguide Mesh Room Acoustic Models The aim of this research is to provide a solution for listening to the acoustics of Digital Waveguide Mesh (DWM) modelled virtual acoustic spaces. The DWM is a numerical simulation technique that has shown to be appropriate for modelling the propogation of sound through air. Recent work has explored methods for spatially capturing a soundfield within a virtual acoustic space using spatially distributed receivers based on sound intensity probe theory. This technique is now extended to facilitate spatial encoding using second-order spherical harmonics. This is achieved through an array of pressure sensitive receivers arranged around a central reference point, with appropriate processing applied to obtain the second-order harmonic signals associated with Ambisonic encoding/decoding. The processed signals are tested using novel techniques in order to objectively assess their integrity for reproducing a faithful impression of the virtual soundfield over a multi-channel sound system.
Download Hyper-Dimensional Digital Waveguide Mesh for Reverberation Modeling Characteristics of digital waveguide meshes with more than three physical dimensions are studied. Especially, the properties of a 4-D mesh are analyzed and compared to waveguide structures of lower dimensionalities. The hypermesh produces a response with a dense and irregular modal pattern at high frequencies, which is beneficial in modeling the reverberation of rooms or musical instrument bodies. In addition, it offers a high degree of decorrelation between output points selected at different locations, which is advantageous for multi-channel reverberation. The frequencydependent decay of the hypermesh response can be controlled using boundary filters introduced recently by one of the authors. Several hypermeshes can be effectively combined in a multirate system, in which each mesh produces reverberation on a finite frequency band. The paper presents two hypermesh application examples: the modeling of the impulse response of a lecture hall and the simulation of the response of a clavichord soundbox.
Download Ray Acoustics Using Computer Graphics Technology The modeling of room acoustics and simulation of sound wave propagation remain a difficult and computationally expensive task. Two main techniques have evolved, with one focusing on a real physical - wave-oriented - sound propagation, while the other approximates sound waves as rays using raytracing techniques. Due to many advances in computer science, and especially computer graphics over the last decade, interactive 3D sound simulations for complex and dynamic environments are within reach. In this paper we analyze sound propagation in terms of acoustic energy and explore the possibilities to map these concepts to radiometry and graphics rendering equations. Although we concentrate on ray-based techniques, we also partially consider wavebased sound propagation effects. The implemented system exploits modern graphics hardware and rendering techniques and is able to efficiently simulate 3D room acoustics, as well as to measure simplified personal HRTFs through acoustic raytracing.
Download Implementing Digital Audio Effects Using a Hardware/Software Co-Design Approach Digital realtime audio effects as of today are realized in software in almost all cases. The hardware platforms used for this purpose reach from multi purpose processors like the Intel Pentium class over embedded processors (e.g. the ARM family) to specialized DSP. The upcoming technology of complete systems on a single programmable chip contrasts such a software centric solution, because it combines software and hardware via some co-design methodology and makes for a promising alternative for the future of realtime audio. Such systems are able to combine the vast amount of computing power provided by dedicated hardware with the flexibility offered by software in a way the designer is free to influence. While the main realization vehicles for these systems – FPGAs – were already promising but unfortunately offered limited possibilities a decade ago [1] they have made rapid progress over the years being one of the product classes that drive the silicon technology of tomorrow. We describe an example for such a realtime digital effects system which was developed using a hardware/software co-design method. While digital realtime audio processing takes place in low latency dedicated hardware units the control and routing of audio streams is done by software running on a 32 bit NIOS II softcore processor. Implementation of the hardware units is done using a DSP centric methodology for raising the abstraction level of VHDL descriptions while still making use of standard of the shelf FPGA synthesis tools. The physical implementation of the complete system uses a rapid prototyping board tailored for communications and audio applications based on an Altera Cyclone II FPGA.
Download Binaural Source Separation in Non-Ideal Reverberant Environments This paper proposes a framework for separating several speech sources in non-ideal, reverberant environments. A movable human dummy head residing in a normal office room is used to model the conditions humans experience when listening to complex auditory scenes. Before the source separation takes place the human dummy head explores the auditory scene and extracts characteristics the same way as humans would do, when entering a new auditory scene. These extracted features are used to support several source separation algorithms that are carried out in parallel. Each of these algorithms estimates a binary time-frequency mask to separate the sources. A combination stage infers a final estimate of the binary mask to demix the source of interest. The presented results show good separation capabilities in auditory scenes consisting of several speech sources.
Download Spatial Track Transition Effects for Headphone Listening In this paper we study the use of different spatial processing techniques to create audio effects for forced transitions between music tracks in headphone listening. The audio effect encompasses a movement of the initially playing track to the side of the listener while the next track to be played moves into a central position simultaneously. We compare seven different methods for creating this effect in a listening test where the task of the user is to characterize the span of the spatial movement of audio play list items around the listener’s head. The methods used range from amplitude panning up to full Head Related Transfer Function (HRTF) rendering. It is found that a computationally efficient method using time-varying interaural time differences is equally effective in creating a large spatial span as the full HRTF rendering method.
Download Monophonic Source Localization for a Distributed Audience in a Small Concert Hall The transfer of multichannel spatialization schemes from the studio to the concert hall presents numerous challenges to the contemporary spatial music composer or engineer. The presence of a reverberant listening environment coupled with a distributed audience are significant factors in the presentation of multichannel spatial music. This paper presents a review of the existing research on the localization performance of various spatialization techniques and their ability to cater for a distributed audience. As the firststep in a major comparative study of such techniques, the results of listening tests for monophonic source localization for a distributed audience in a reverberant space are presented. These results provide a measure of the best possible performance that can be expected from any spatialization technique under similar conditions. Keywords: Sound localization, distributed audience, spatial music.
Download Synthesis of a Macro Sound Structure within a Self Organizing System This paper is focused on synthesizing macro-sound structures with certain ecological attributes to obtain perceptually interesting and compositionally useful results. The system, which delivers the sonic result is designed as a self organizing system. Certain principles of cybernetics are critically assessed in the paper in terms of interdependencies among system components, system dynamics and the system/environment coupling. It is aiming towards a self evolution of an ecological kind, applying an interactive exchange with its external conditions. The macro-organization of the sonic material is a result of interactions of events at a meso and micro level but also this exchange with its environment. The goal is to formulate some new principles and present its sketches here by arriving to a network of concepts suggesting new ideas in sound synthesis.
Download Characteristics of Broken-Line Approximation and Its Use in Distortion Audio Effects This paper deals with an analytic solution of spectrum changes in scalar non-linear discrete systems without memory, whose transfer characteristics can be approximated via broken-line function. The paper also deals with relations between the harmonics ratio and the approximation parameters. Furthermore, the dependence of the harmonics ratio on the amplitude of a harmonic input signal is presented for the most common characteristics that are approximated via broken-line function. These characteristics are judged from the dissonance point of view.