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    ABSTRACT: In this paper, a method for modeling diffusive boundaries in finite-difference time-domain (FDTD) room acoustics simulations with the use of impedance filters is presented. The proposed technique is based on the concept of phase grating diffusers, and realized by designing boundary impedance filters from normal-incidence reflection filters with added delay. These added delays, that correspond to the diffuser well depths, are varied across the boundary surface, and implemented using Thiran allpass filters. The proposed method for simulating sound scattering is suitable for modeling high frequency diffusion caused by small variations in surface roughness and, more generally, diffusers characterized by narrow wells with infinitely thin separators. This concept is also applicable to other wave-based modeling techniques. The approach is validated by comparing numerical results for Schroeder diffusers to measured data. In addition, it is proposed that irregular surfaces are modeled by shaping them with Brownian noise, giving good control over the sound scattering properties of the simulated boundary through two parameters, namely the spectral density exponent and the maximum well depth.
    IEEE Transactions on Audio Speech and Language Processing 04/2011;
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    ABSTRACT: This paper presents methods for simulating room acoustics using the finite-difference time-domain (FDTD) technique, focusing on boundary and medium modeling. A family of nonstaggered 3-D compact explicit FDTD schemes is analyzed in terms of stability, accuracy, and computational efficiency, and the most accurate and isotropic schemes based on a rectilinear grid are identified. A frequency-dependent boundary model that is consistent with locally reacting surface theory is also presented, in which the wall impedance is represented with a digital filter. For boundaries, accuracy in numerical reflection is analyzed and a stability proof is provided. The results indicate that the proposed 3-D interpolated wideband and isotropic schemes outperform directly related techniques based on Yee's staggered grid and standard digital waveguide mesh, and that the boundary formulations generally have properties that are similar to that of the basic scheme used.
    IEEE Transactions on Audio Speech and Language Processing 02/2011;
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    ABSTRACT: We refer to ??Virtual Analog?? (VA) as a wide class of digital implementations that are modeled after nonlinear analog circuits for generating or processing musical sounds. The reference analog system is therefore typically represented by a set of blocks that are connected with each other through electrical ports, and usually exhibits a nonlinear behavior. It therefore seems quite natural to consider Nonlinear Wave Digital modeling as a solid approach for the rapid prototyping of such systems. In this paper, we discuss how nonlinear wave digital modeling can be fruitfully used for this purpose, with particular reference to special blocks and connectors that allow us to overcome the implementational difficulties and potential limitations of such solutions. In particular, we address some issues that are typical of VA and physical modeling, concerning how to accommodate special blocks into WD structures, how to enable the interaction between different WD structures, and how to accommodate structural and topological changes on the fly.
    IEEE Transactions on Audio Speech and Language Processing 06/2010;
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    ABSTRACT: This paper describes the use of physiological and kinematic sensors for the direct measurement of physical gesture and emotional changes in live musical performance. Initial studies on the measurement of performer and audience emotional state in controlled environments serve as the foundation for three pieces using the BioMuse system in live performance. By using both motion and emotion to control sound generation, the concept of integral music control has been achieved.
    Affective Computing and Intelligent Interaction and Workshops, 2009. ACII 2009. 3rd International Conference on; 10/2009
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    ABSTRACT: This paper describes the development of a framework that allows virtual object contact sounds to be synthesised in real time from information provided by a governing physics engine at physics refresh rate. The objects can be modified during run-time by their physical or perceptual parameters and both impact and continuous contact sounds can be created. The new contributions are features designed to give the user control over how objects look, sound and behave physically. This is to help pave the way for innovations involving object manipulation and sounding and in particular a tool/game in which composers/gamers can create sounds and music that is driven by physics and accompanied by animation is envisaged.
    Games Innovations Conference, 2009. ICE-GIC 2009. International IEEE Consumer Electronics Society's; 09/2009
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    ABSTRACT: The numerical issues involved in modelling measured room transfer functions (RTFs) are examined. This is explored using a nonlinear parametric estimation technique known as the decimated Pade' approximant (DPA). The DPA combines the well-known methodology of Pade' rational polynomial approximation with beamspace windowing. This combination helps to overcome the severe numerical instabilities encountered in calculations with large data records. The aim is to accurately extract the parameters that reliably quantify the analytic structure of signals composed of decaying sinusoidal oscillations. DPA parameter estimation provides the ability to construct a high-resolution spectral estimate of such signals for either specific spectral regions or the entire Nyquist interval. As demonstrated in the authors' previous work (O'Sullivan and Cowan, 2006), this technique, developed in quantum chemistry, readily cross-fertilises to the field of acoustics, where it can fully reconstruct the complicated spectra of experimental RTFs. A noise-filtering technique using the removal of Froissart doublets to obtain an irreducible rational model is investigated. This noise filtering can be used to find an order of the parametric model that is inherent in the data. Additionally, an example is shown suggesting that such a process may be useful in room spatialisation problems.
    IET Signal Processing 07/2008;
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    ABSTRACT: Fluid dynamical analysis and time-domain modelling of a single reed-mouthpiece-lip system can be used to inform the formulation of a lumped model of the woodwind excitation mechanism. Coupling this lumped model to a model of the instrument bore enables computationally efficient generation of sustained oscillations, using a small number of physical parameters that define the instrument and the way the player controls them. As such, the embouchure of the player as well as the geometry of the system is taken into account. In this paper, an attempt is carried out to use the numerically generated sound as an input to an inversion algorithm for the reed-mouthpiece-lip system. Assuming that the reed motion is proportional to the pressure difference across it, a relationship can be established between the pressure and the total flow inside the mouthpiece that allows a first estimation of the physical parameters using standard optimisation techniques. Currently we are undertaking efforts to apply the inversion to data measured under real playing conditions, i.e. effectively capturing player gesture information in the form of physical control parameters.
    The Journal of the Acoustical Society of America 06/2008; 123(5):3123.
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    ABSTRACT: Knowledge of the forward and backward traveling waves inside the bore of a wind instrument is a useful starting point for the estimation of its playing parameters. These are mainly parameters describing the mouthpiece embouchure and the states of the tone holes. Due to the highly nonlinear behaviour of the excitation mechanism, a precise estimation is needed. The separation method under investigation relies on a model inversion, starting from the pressure measured by three microphones. For this reason the estimation is very sensitive to the relative positions of the microphones, and the latter must therefore be known very precisely. A geometrical measurement would not be reliable because of construction tolerances, including uncertainties about the acoustic centers of the microphones; therefore the distances are gathered through audio measurements. A number of approaches to such a calibration of the measurement system have been investigated, using a purposely constructed apparatus which will also be described.
    The Journal of the Acoustical Society of America 06/2008; 123(5):3016.
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    ABSTRACT: In this paper, we present new methods for constructing and analysing frequency-dependent boundaries in room acoustic modelling with the use of finite difference time domain (FDTD) techniques. Novel FDTD formulations of simple locally reacting wall models with complex impedance are proposed and analysed in terms of pressure wave reflectance for different wall impedances and angles of incidence. The analysis is done using both numerical experiments and analytic evaluation. For the numerical experiments, a compact implicit scheme of 4th-order accuracy is used for updating the room interior grid points, the results of which are analysed in both time and frequency domains. The simulation results show that the 2D frequency-dependent locally reacting wall models adhere well to their theoretical counterparts, particularly at low frequencies. Furthermore, they validate the analytic evaluation method, which paves the way for using either method as a tool for analysis of numerical reflectance.
    Communications, Control and Signal Processing, 2008. ISCCSP 2008. 3rd International Symposium on; 04/2008
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    ABSTRACT: A time-domain formulation of a lumped model approximation of a clarinet reed excitation mechanism is presented. The lumped model is based on an analytical representation of the flow within the reed channel, incorporating a contraction coefficient (vena contracta factor) that is defined as the ratio of the effective flow over the Bernoulli flow. This coefficient has been considered to be constant in previous studies focusing on sound synthesis. In this paper it will be treated as a function of the reed opening, varying between 0 and 1 as predicted by boundary layer flow theory. Focussing on a specific mouthpiece geometry, the effect of modelling a variable air jet height on the synthesised sound is analysed.
    Communications, Control and Signal Processing, 2008. ISCCSP 2008. 3rd International Symposium on; 04/2008
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