Direction of arrival estimation of multiple acoustic sources using a maximum likelihood method in the spherical harmonic domain

© 2018 Elsevier Ltd Direction of arrival estimation (DOA) of multiple acoustic sources has been used for a wide range of applications, including room geometry inference, source separation and speech enhancement. The beamformer-based and subspace-based methods are most commonly used for spherical microphone arrays; however, the former suffers from spatial resolution limitations, while the later suffers from performance degradation in noisy environment. This letter proposes a multiple source DOA estimation approach based on the maximum likelihood method in the spherical harmonic domain and implements an efficient sequential iterative search of maxima on the cost function in the spherical harmonic domain. The proposed method avoids the division of the spherical Bessel function, which makes it suitable for both rigid-sphere and open-sphere configurations. Simulation results show that the proposed method has a significant superiority over the commonly used frequency smoothing multiple signal classification method. Experiments in a normal listening room and a reverberation room validate the effectiveness of the proposed method

Spherical Harmonic Decomposition of a Sound Field Using Microphones on a Circumferential Contour Around a Non-Spherical Baffle

Spherical harmonic\ua0(SH) representations of sound fields are usually obtained from microphone arrays with rigid spherical baffles whereby the microphones are distributed over the entire surface of the baffle. We present a method that overcomes the requirement for the baffle to be spherical. Furthermore, the microphones can be placed along a circumferential contour around the baffle. This greatly reduces the required number of microphones for a given spatial resolution compared to conventional spherical arrays. Our method is based on the analytical solution for SH\ua0decomposition based on observations along the equator of a rigid sphere that we presented recently. It incorporates a calibration stage in which the microphone signals due to a suitable set of calibration sound fields are projected onto the SH\ua0decomposition of those same sound fields on the surface of a notional rigid sphere by means of a linear filtering operation. The filter coefficients are computed from the calibration data via a least/squares fit. We present an evaluation of the method based on the application of binaural rendering of the SH\ua0decomposition of the signals from an 18/element array that uses a human head as the baffle and that provides 8th ambisonic order. We analyse the accuracy and robustness of our method based on simulated data as well as based on measured data from a prototype

Numerical relativity with the conformal field equations

I discuss the conformal approach to the numerical simulation of radiating isolated systems in general relativity. The method is based on conformal compactification and a reformulation of the Einstein equations in terms of rescaled variables, the so-called ``conformal field equations'' developed by Friedrich. These equations allow to include ``infinity'' on a finite grid, solving regular equations, whose solutions give rise to solutions of the Einstein equations of (vacuum) general relativity. The conformal approach promises certain advantages, in particular with respect to the treatment of radiation extraction and boundary conditions. I will discuss the essential features of the analytical approach to the problem, previous work on the problem - in particular a code for simulations in 3+1 dimensions, some new results, open problems and strategies for future work.Comment: 34 pages, submitted to the Proceedings of the 2001 Spanish Relativity meeting, eds. L. Fernandez and L. Gonzalez, to be published by Springer, Lecture Notes in Physics serie

Visualizing Interior And Exterior Jet Aircraft Noise

In today\u27s competitive aerospace industry, the quest for quiet has drawn significant attention to both the interior and exterior design of an airplane. Understanding the noise generation mechanisms of a jet aircraft is a crucial first step toward developing the most cost-effective noise and vibrations abatement methods. In this investigation, the Helmholtz Equation Least Squares (HELS) based nearfield acoustic holography will be used to understand noise transmission caused by jet engine and turbulence into the fuselage of a jet aircraft cruising at 30,000 ft. Modern propulsive jet engines produce exterior noise sources with a high amplitude noise field and complicated characteristics, which makes them very difficult to characterize. In particular, there are turbulent eddies that are moving through the jet at high speeds along the jet boundary. These turbulent eddies in the shear layer produce a directional and frequency dependent noise. The original HELS approach assumes a spherical source at the origin and computes the acoustic field based on spherical emission from this source. This assumption of one source at the origin is not sufficient to characterize a complex source like a jet. As such, a modified HELS approach is introduced that will help improve the source characterization as it is not dependent on a single source at the origin but a number of virtual sources throughout the space. Custom microphones are created to take acoustic pressure measurements around the jet engine. These measured acoustic pressures are then taken as input to the modified HELS algorithm to visualize the noise pattern of a subsonic jet engine

Efficient modeling of sound source radiation in free-space and room environments

Motivated by the need to develop efficient acoustics simulations for sources in different room environments, a modeling procedure has been proposed that consists of two steps in general: (1) the modeling of the free-space radiation of the source based on measurements in a anechoic environment, and (2) the prediction of the sound field in a room environment based on that free-space information. To achieve a high modeling efficiency, i.e., to reduce the number of modeling parameters while still maintaining acceptable accuracy, a Multipole Equivalent Source Model (ESM) with undetermined source locations has been developed for the free-space sound field prediction. In contrast with traditional ESM’s, or acoustical holography methods in general, the model developed in the present work possesses two efficiency improvements: (1) the use of the series of monopoles, dipoles, quadrupoles, etc. as equivalents sources (since in predicting the sound field, the multipole series can be simply represented as closely located monopoles) and (2) the flexibility of using spatially separated sources with undetermined locations. In the inverse parameter estimation process of this method, the calculation of the source strengths is linear while the source locations are determined by a nonlinear optimization procedure. It is shown, by an experimental validation, that the prediction using this method can be accurate for almost the whole audio frequency range. To model the sound field at high frequencies specifically, different types of methods using local-basis functions were developed. At high frequencies, the spatial variation of the sound field is usually large and thus the number of measurements points in space is likely not to be enough to model a relatively complicated source if a traditional equivalent source model is used, and the under-sampling errors from all regions will accumulate to affect the predictions in any particular region. However, if localized basis functions are used to represent the sound field, the under-sampling errors from different regions do not affect each other. Two types of local-basis method are developed in this work: one based on piece-wise polynomial interpolation (which is limited to having only a single source) and the other based on least squares (which can be applied to multiple sources and even to interior problems). Simulation results have shown that these local-basis methods, at very high frequencies, can achieve good overall prediction accuracy with only a loss of some details in the spatial variation of the sound field. In the room acoustics modeling section, the Equivalent Source Method is modified and implemented which, compared with the geometric acoustics models, gives a prediction based on a more rigorous mathematical foundation and, compared with Boundary Element methods, reduces the computational intensity. In this proposed room acoustics ESM, the free-space source radiation is assumed known, and the room component sound field is determined by an ESM. Differing from the free-space ESMs, this room acoustics ESM (1) contains additional equivalent sources representing the incoming waves, and (2) uses impedance boundary conditions on the surfaces instead of the measured sound field, to estimate the source strengths. It is validated by simulations (in both 2D and 3D spaces) and then by experiments that the proposed room acoustics ESM can be used as a reduced order modeling technique in simulating the sound field in a room. It is also shown that the prediction accuracy and the computational load can be flexibly balanced, if Multipole ESMs are used, by selecting an appropriate maximum source order

The Cauchy Problem for the Einstein Equations

Various aspects of the Cauchy problem for the Einstein equations are surveyed, with the emphasis on local solutions of the evolution equations. Particular attention is payed to giving a clear explanation of conceptual issues which arise in this context. The question of producing reduced systems of equations which are hyperbolic is examined in detail and some new results on that subject are presented. Relevant background from the theory of partial differential equations is also explained at some lengthComment: 98 page

Effects of errorless learning on the acquisition of velopharyngeal movement control

Session 1pSC - Speech Communication: Cross-Linguistic Studies of Speech Sound Learning of the Languages of Hong Kong (Poster Session)The implicit motor learning literature suggests a benefit for learning if errors are minimized during practice. This study investigated whether the same principle holds for learning velopharyngeal movement control. Normal speaking participants learned to produce hypernasal speech in either an errorless learning condition (in which the possibility for errors was limited) or an errorful learning condition (in which the possibility for errors was not limited). Nasality level of the participants’ speech was measured by nasometer and reflected by nasalance scores (in %). Errorless learners practiced producing hypernasal speech with a threshold nasalance score of 10% at the beginning, which gradually increased to a threshold of 50% at the end. The same set of threshold targets were presented to errorful learners but in a reversed order. Errors were defined by the proportion of speech with a nasalance score below the threshold. The results showed that, relative to errorful learners, errorless learners displayed fewer errors (50.7% vs. 17.7%) and a higher mean nasalance score (31.3% vs. 46.7%) during the acquisition phase. Furthermore, errorless learners outperformed errorful learners in both retention and novel transfer tests. Acknowledgment: Supported by The University of Hong Kong Strategic Research Theme for Sciences of Learning © 2012 Acoustical Society of Americapublished_or_final_versio

Dark Energy: Observational Evidence and Theoretical Models

The book elucidates the current state of the dark energy problem and presents the results of the authors, who work in this area. It describes the observational evidence for the existence of dark energy, the methods and results of constraining of its parameters, modeling of dark energy by scalar fields, the space-times with extra spatial dimensions, especially Kaluza---Klein models, the braneworld models with a single extra dimension as well as the problems of positive definition of gravitational energy in General Relativity, energy conditions and consequences of their violation in the presence of dark energy. This monograph is intended for science professionals, educators and graduate students, specializing in general relativity, cosmology, field theory and particle physics.Comment: Book, 380 p., 88 figs., 7 tables; 1st volume of three-volume book "Dark energy and dark matter in the Universe", ed. V. Shulga, Kyiv, Academperiodyka, 2013; ISBN 978-966-360-239-4, ISBN 978-966-360-240-0 (vol. 1). arXiv admin note: text overlap with arXiv:0706.0033, arXiv:1104.3029 by other author

Mathematical Aspects of General Relativity (hybrid meeting)

General relativity is an area that naturally combines differential geometry, partial differential equations, global analysis and dynamical systems with astrophysics, cosmology, high energy physics, and numerical analysis. It is rapidly expanding and has witnessed remarkable developments in recent years