Etienne Corteel

Synthesis of directional sources using wave field synthesis, possibilities, and limitations

The synthesis of directional sources using wave field synthesis is described. The proposed formulation relies on an ensemble of elementary directivity functions based on a subset of spherical harmonics. These can be combined to create and manipulate directivity characteristics of the synthesized virtual sources. The WFS formulation introduces artifacts in the synthesized sound field for both ideal and real loudspeakers. These artifacts can be partly compensated for using dedicated equalization techniques. A multichannel equalization technique is shown to provide accurate results thus enabling for the manipulation of directional sources with limited reconstruction artifacts. Applications of directional sources to the control of the direct sound field and the interaction with the listening room are discussed.

Real-time rendering of dynamic scenes using wave field synthesis

Wave field synthesis (WFS) methods, combined with the MPEG-4 multimedia standard, allow us to capture, transmit and reproduce time-varying acoustic scenes, such as theatre events with moving actors in a concert hall, in a perceptually realistic way for groups of listeners in a defined listening area. In this paper, we present related techniques that have been developed within the European project Carrouso.

SMART-I 2 : “Spatial multi-user audio-visual real-time interactive interface”, A broadcast application context

SMART-I2 is a high quality 3D audio-visual interactive rendering system. In SMART-I2, the screen is also used as a multichannel loudspeaker. The spatial audio rendering is based on Wave Field Synthesis, an approach that creates a coherent spatial perception of a spatial sound scene over a large listening area. The azimuth localization accuracy of the system has been verified by a perceptual experiment. Contrary to conventional systems, SMART-I2 is able to realize a high degree of 3D audio-visual integration with almost no compromise on either the audio or the graphics rendering quality. Such a system can provide benefits to a wide range of applications.

Radiation control applied to sound synthesis: An attempt for ‘‘spatial additive synthesis.’’

Sound synthesis is generally focused on the reproduction of the spectral characteristics of the source or on the simulation of its physical behavior. Less attention is paid to the sound playback step which generally results in a simple diffusion on a conventional loudspeaker setup. Stating the perceptual importance of a faithful reproduction of the source radiation properties, the paper presents a method combining a synthesis engine, based on physical modeling, with a rendering system allowing an accurate control on the produced sound‐field. Two sound‐field synthesis models are considered. In the first one, a local 3D array of transducers is controlled by signal processing for creating elementary directivity patterns that can be further combined in order to shape a more complex radiation. The dual approach consists in surrounding the audience with transducer arrays driven by wave field synthesis in order to simulate the sound field associated to these elementary directivity patterns. In both cases, the di...

A design space for three-dimensional curve edition

Designing and editing 3D curves is often involved in a wide array of applications such as CAD, multimedia content edition or landscape and road generation. This diversity resulted in a spread of 3D-related works across different communities such as SIGCHI or SIGGRAPH. In this article, we introduce a design space to gather existing techniques in the field of 3D curves creation and edition. This design space is built around two axes: system and language, in order to describe and compare existing techniques.

Diffraction formulation for the sound radiation of a loudspeaker on a rigid convex edged shape enclosure

We present a method for calculating the sound radiation of a loudspeaker on a box-shape enclosure. This method is based on the iterative Asheim-Svensson formulation [Asheim et al. J. Acoust. Soc. Am., 2013]. In this geometrical acoustical model, the radiated sound is given by the addition of the direct sound of a baffled piston and the sound scattered by the edges of the loudspeaker enclosure. The latter are expressed in the form of multiple-order edge diffraction components. This method becomes particularly attractive at high frequencies since the maximum order required to get a correct estimation decreases with frequency. Altogether, the method becomes less costly than the Boundary Element Method (BEM) beyond a given frequency. The convergence of the method can be estimated by considering the distance traveled by the creeping wave on the enclosure instead of considering the successive orders of diffraction by each edge. An iterative formulation follows which is well-suited to slender objects such as a s...

A spheroid model for the sound radiation of a loudspeaker on a sound bar

The sound radiation of a loudspeaker on a sound bar with a slender shape is analyzed. Measurements and boundary element method (BEM) simulations of a rectangular rigid enclosure with a flat piston turn out to be in close agreement up to the frequency limit imposed by the discretization chosen for the BEM. Looking up for a shorter computation time, we consider an analytic model based on a geometrical approximation of the sound bar by a prolate spheroid. The corresponding spheroidal coordinate system allows for an analytical solution of the sound-radiation problem. The following parameters are adjusted: geometry of the ellipse-based spheroid, size and location of the circular piston, minimum order of the spheroidal wave functions that ensures convergence. In the light of the BEM results, we also predict the frequency validity of the analytic model. In order to improve the control of the acoustical field radiated by a sound bar, we discuss the influence of the enclosure edges on the regularity of the sound f...

Impact of spatial audiovisual coherence on source unmasking

The influence of the spatial audiovisual coherence is evaluated in the context of a video recording of live music. In this context, audio engineers currently balance the audio spectrum to unmask each music instrument getting it intelligible inside the stereo mix. In contrast, sound engineers using spatial audio technologies have reported that sound source equalization is unnecessary in live music mixing when the sound sources are played at the same location of the physical instruments. The effects of spatial audiovisual coherence and sound spatialization have been assessed: expert subjects were asked to compare two mixes in audio only and in audiovisual mode. For this aim, music concerts were visually projected and audio rendered using WFS. Three sound engineers did the audio mixing for all pieces of music in the same room were the test have been carried out.

Subjective and objective evaluation of localisation accuracy in wave field sysnthesis

Wave Field Synthesis (WFS) is a holophonic technique that relies on the reproduction of physical properties of sound fields in an extended listening area. Limitations of this technique are due to approximations regarding the mathematical basis and have been studied in [Ber88] [dB04]. The synthesis remains correct up to a corner frequency referred to as the spatial aliasing frequency and inside an area limited by the length of the WFS array and the position of the virtual sources. A Multichannel Equalization filter (MEQ) is applied to the driving limentation signals of the loudspeakers, as described in [Cor06]. The aim of the present study is to evaluate localisation in WFS depending on both listening and source positions. An objective analysis of the binaural signals is compared to the results of a localisation task for which spatialised high-pass filtered white noises served as stimuli. The results of the psycho-acoustic test are compared to the binaural localisation cues, namely ITD (interaural time dierences) and ILD (interaural level dierences). Above the aliasing frequency, ITD and ILD are conflicting and ILD errors account in most cases for the perceptual errors.