This thesis investigates the design and the analysis of acoustic signal processing algorithms in reverberant rooms. Reverberation poses a major challenge to acoustic signal processing problems. It degrades speech intelligibility and causes many acoustic algorithms that process sound to perform poorly. Current solutions to the reverberation problem frequently only work in lightly reverberant environments. There is need to improve the reverberant performance of acoustic algorithms.¶ The approach of this thesis is to explore how the intrinsic properties of reverberation can be exploited to improve acoustic signal processing algorithms. A general approach to soundfield modelling using statistical room acoustics is applied to analyze the reverberant performance of several acoustic algorithms. A model of the underlying structure of reverberation is incorporated to create a new method of soundfield reproduction.¶ Several outcomes resulting from this approach are: (i) a study of how more sound capture with directional microphones and beamformers can improve the robustness of acoustic equalization, (ii) an assessment of the extent to which source tracking can improve accuracy of source localization, (iii) a new method of soundfield reproduction for reverberant rooms, based upon a parametrization of the acoustic transfer function and (iv) a study of beamforming to directional sources, specifically exploiting the directionality of human speech.¶ The approach to soundfield modelling has permitted a study of algorithm performance on important parameters of the room acoustics and the algorithm design. The performance of acoustic equalization and source tracking have been found to depend not only on the levels of reverberation but also on the correlation of pressure between points in reverberant soundfields. This correlation can be increased by sound capture with directional capture devices. Work on soundfield reproduction has shown that, though reverberation significantly degrades the performance of conventional techniques, by accounting for the reverberation it is possible to design reproduction methods that function well in reverberant environments.

Research investigating the behavioral and physiological responses of bats to echoes typically includes analysis of acoustic signals from microphones and/or microphone arrays, using time difference of arrival (TDOA) between array elements or the microphones to locate flying bats (azimuth and elevation). This has provided insight into transmission adaptations with respect to target distance, clutter, and interference. Microphones recording transmitted signals and echoes near a stationary bat provide sound pressure as a function of time but no directional information. This dissertation introduces spatial audio techniques to bat biosonar studies as a complementary method to the current TDOA based acoustical study methods. This work proposes a couple of feasible methods based on spatial audio techniques, that both track bats in flight and pinpoint the directions of echoes received by a bat. A spatial audio/soundfield microphone array is introduced to measure sounds in the sonar frequency range (20-80 kHz) of the big brown bat (Eptesicus fuscus). The custom-built ultrasonic tetrahedral soundfield microphone consists of four capacitive microphones that were calibrated to match magnitude and phase responses using a transfer function approach. Ambisonics, a signal processing technique used in three-dimensional (3D) audio applications, is used for the basic processing and reproduction of the signals measured by the soundfield microphone. Ambisonics provides syntheses and decompositions of a signal containing its directional properties, using the relationship between the spherical harmonics and the directional properties. As the first proposed method, a spatial audio decoding technique called HARPEx (High Angular Resolution Planewave Expansion) was used to build a system providing angle and elevation estimates. HARPEx can estimate the direction of arrivals (DOA) for up to two simultaneous sources since it decomposes a signal into two dominant planewaves. Experiments proved that the estimation system based on HARPEx provides accurate DOA estimates of static or moving sources. It also reconstructed a smooth flight-path of a bat by accurately estimating its direction at each snapshot of pulse measurements in time. The performance of the system was also assessed using statistical analyses of simulations. A signal model was built to generate microphone capsule responses to a virtual source emitting an LFM signal (3 ms, two harmonics: 40-22 kHz and 80-44 kHz) at an angle of 30° in the simulations. Medians and RMSEs (root-mean-square error) of 10,000 simulations for each case represent the accuracy and precision of the estimations, respectively. Results show lower d (distance between a capsule and the soundfield microphone center) or/and higher SNR (signal-to-noise ratio) are required to achieve higher estimator performance. The Cramer-Rao lower bounds (CRLB) of the estimator are also computed with various d and SNR conditions. The CRLB which is for TDOA based methods does not cover the effects of different incident angles to the capsules and signal delays between the capsules due to a non-zero d, on the estimation system. This shows the CRLB is not a proper tool to assess the estimator performance. For the second proposed method, the matched-filter technique is used instead of HARPEx to build another estimation system. The signal processing algorithm based on Ambisonics and the matched-filter approach reproduces a measured signal in various directions, and computes matched-filter responses of the reproduced signals in time-series. The matched-filter result points a target(s) by the highest filter response. This is a sonar-like estimation system that provides information of the target (range, direction, and velocity) using sonar fundamentals. Experiments using a loudspeaker (emitter) and an artificial or natural target (either stationary or moving) show the system provides accurate estimates of the target's direction and range. Simulations of imitating a situation where a bat emits a pulse and receives an echo from a target (30°) were also performed. The echo sound level is determined using the sonar equation. The system processed the virtual bat pulse and echo, and accurately estimated the direction, range, and velocity of the target. The simulation results also appear to recommend an echo level over -3 dB for accurate and precise estimations (below 15% RMSE for all parameters). This work proposes two methods to track bats in flight or/and pinpoint the directions of targets using spatial audio techniques. The suggested methods provide accurate estimates of the direction, range, or/and velocity of a bat based on its pulses or of a target based on echoes. This demonstrates these methods can be used as key tools to reconstruct bat biosonar. They would be also an independent tool or a complementary option to TDOA based methods, for bat echolocation studies. The developed methods are believed to be also useful in improving man-made sonar technology. / Doctor of Philosophy / While bats are one of the most intriguing creatures to the general population, they are also a popular subject of study in various disciplines. Their extraordinary ability to navigate and forage irrespective of clutter using echolocation has gotten attention from many scientists and engineers. Research investigating bats typically includes analysis of acoustic signals from microphones and/or microphone arrays. Using time difference of arrival (TDOA) between the array elements or the microphones is probably the most popular method to locate flying bats (azimuth and elevation). Microphone responses to transmitted signals and echoes near a bat provide sound pressure but no directional information. This dissertation proposes a complementary way to the current TDOA methods, that delivers directional information by introducing spatial audio techniques. This work shows a couple of feasible methods based on spatial audio techniques, that can both track bats in flight and pinpoint the directions of echoes received by a bat. An ultrasonic tetrahedral soundfield microphone is introduced as a measurement tool for sounds in the sonar frequency range (20-80 kHz) of the big brown bat (Eptesicus fuscus). Ambisonics, a signal processing technique used in three-dimensional (3D) audio applications, is used for the basic processing of the signals measured by the soundfield microphone. Ambisonics also reproduces a measured signal containing its directional properties. As the first method, a spatial audio decoding technique called HARPEx (High Angular Resolution Planewave Expansion) was used to build a system providing angle and elevation estimates. HARPEx can estimate the direction of arrivals (DOA) for up to two simultaneous sound sources. Experiments proved that the estimation system based on HARPEx provides accurate DOA estimates of static or moving sources. The performance of the system was also assessed using statistical analyses of simulations. Medians and RMSEs (root-mean-square error) of 10,000 simulations for each simulation case represent the accuracy and precision of the estimations, respectively. Results show shorter distance between a capsule and the soundfield microphone center, or/and higher SNR (signal-to-noise ratio) are required to achieve higher performance. For the second method, the matched-filter technique is used to build another estimation system. This is a sonar-like estimation system that provides information of the target (range, direction, and velocity) using matched-filter responses and sonar fundamentals. Experiments using a loudspeaker (emitter) and an artificial or natural target (either stationary or moving) show the system provides accurate estimates of the target's direction and range. Simulations imitating a situation where a bat emits a pulse and receives an echo from a target (30°) were also performed. The system processed the virtual bat pulse and echo, and accurately estimated the direction, range, and velocity of the target. The suggested methods provide accurate estimates of the direction, range, or/and velocity of a bat based on its pulses or of a target based on echoes. This demonstrates these methods can be used as key tools to reconstruct bat biosonar. They would be also an independent tool or a complementary option to TDOA based methods, for bat echolocation studies. The developed methods are also believed to be useful in improving sonar technology.

Il y a plus d'un siècle, les conditions de travail ont fortement évolué sous l'influence de l'industrialisation et notamment à partir de nouvelles méthodes de travail du type Tayloriennes. Des bureaux ouverts à l'Action Office des années 50, c'est plus de 60% de la population active qui est concernée aujourd'hui en Europe. L'évolution des réglementations, liée à la prise de conscience collective des effets psychosomatiques des nuisances sonores, entraîne l'implication par les maîtrises d'ouvrages de bureaux d'études acoustiques pour la préconisation et la mise en œuvre dans la construction et la réhabilitation des espaces tertiaires. La rencontre d'acteurs scientifiques et industriels a donné lieu à ce travail de thèse, étudiant la propagation de l'énergie acoustique pour des espaces dont une des dimensions est différente des autres.La méthode se réduit à la conservation du tenseur énergie-impulsion puis à un système d'équations couplées sur l'intensité acoustique et sur la densité d'énergie. C'est un système hyperbolique d'équations linéaires aux dérivés partielles du premier ordre. Une méthode d'intégration sur une à deux dimensions de l'espace permet d'introduire les coefficients d'absorption et de diffusion moyens. Nous introduisons le potentiel d'intensité et nous écrivons le système sous la forme d'une équation hyperbolique linéaire aux dérivées partielles du second ordre impliquant la densité d'énergie, l'intensité acoustique ou le potentiel d'intensité sur une ou deux dimensions. Nous proposons une méthode analytique approchée permettant de vérifier les résultats à une dimension.Pour la conception acoustique des plateaux de bureaux, la modélisation informatique est un outil remarquable souffrant pourtant de limitations restreignant ses applications. Nous résolvons le formalisme introduit dans ce travail par la méthode des différences finies dans le domaine temporel sur une et deux dimensions. Les schémas utilisés sont stables et explicites et peu couteux en mémoires informatiques. Le fait que nous nous intéressions à une variable énergétique permet de considérer un pas de modélisation spatial important - de l'ordre du mètre - et d'accélérer d'autant les calculs.Le partenariat industriel nous a notamment permis d'accéder à des espaces de type plateaux de bureaux. Nous comparons les résultats des modélisations avec des mesures in situ conduites avec un microphone SoundField ST250 permettant l'estimation de la densité d'énergie et de l'intensité acoustique. / More than a century ago, working conditions have evolved under the influence of industrialization and especially of new management methods such as the Taylorism. From Open-Spaces to Action Offices in the 1950s, more than 60 % of the European working population is concerned today. The evolution of regulations, linked to the collective awareness of the psychosomatic effects of noise, has led clients to request the involvement of acoustical consultants for giving recommendations and supervising their implementation in constructions and rehabilitations of office spaces. This is why scientific and industrial stakeholders joined forces for this thesis dedicated to the propagation of sound energy within rooms characterized by one dimension different from the others.The method developed in this thesis reduces the conservation of the energy-stress tensor to a system of coupled equations for the sound intensity and the sound energy density. It is a hyperbolic system of linear, partial differential equations of first order. Integrating this system on one or two space dimensions leads to the introduction of the mean absorption and diffusion coefficients. We then introduce an intensity potential and write the system in the form of a linear hyperbolic equation involving partial derivatives of second order for the energy density, the sound intensity, or the intensity potential in one or two dimensions. We also propose an analytical approximated method to verify the results in one dimension.For the acoustic design of open-space offices, computer modelling is an outstanding tool. Yet limitations restrict its applications. We solve the equations introduced in this work by the finite-difference time-domain method in the one- and two-dimensional cases. We use stable and explicit schemes that require little computer memory. Considering energy variables allows the use of large spatial steps - of the order of the metre - and accelerates the calculations.The industrial partnership notably gave us access to open-space offices. We compare the results of the modelling with in situ measurements carried out with a SoundField ST250 microphone that makes it possible to estimate the sound energy density and the sound intensity.

Le nombre croissant d'appareils de diffusion de contenus audio pose le problème de partager le même espace physique sans partager lemême espace sonore. Les Sound Zones rendent possible la reproduction de programmes audio indépendants et spatialement séparés, àpartir d'un ensemble de haut-parleurs et de méthodes de reproduction de champs sonores. Le problème est alors décomposé en deuxzones : la Bright zone, où le contenu doit être reproduit et la Dark zone, où il doit être annulé. De nombreuses méthodes existent pourrésoudre ce problème, mais la plupart ne traite que le cas d'auditeurs en position statique. Elles s'appuient sur la résolution directe desméthodes d'optimisation adaptative, telle que la méthode de Pressure Matching (PM). Or, pour des utilisateurs en mouvement, cesméthodes ont un coût de calcul trop élevé, rendant impossible leur application à un problème dynamique. Le but de cette thèse est dedévelopper une solution présentant une complexité compatible avec un contrôle dynamique des Sound Zones, tout en conservant lesperformances des méthodes conventionnelles. Sous l'hypothèse que les déplacements sont lents, une résolution itérative du problème PMest proposée et évaluée. Les algorithmes LMS, NLMS et APA sont comparés sur la base de simulations en champ libre. La méthode LMSs'avère la plus avantageuse en termes de complexité, mais elle souffre d'une erreur de reproduction. Un effet mémoire limitant la réactivitédes algorithmes est aussi mis en évidence. Il est corrigé en implémentant une variante introduisant un facteur d'oubli (Variable LeakyLMS ou VLLMS). / The growing number of audio devices raises the problem of sharing the same physical space without sharing the same sound space. SoundZones make it possible to play independent and spatially separated audio programs by loudspeaker array in combination with sound fieldreproduction methods. The problem is then split into two zones: the Bright zone, where the audio content must be reproduced and theDark zone, where it must be cancelled. There are many methods available to solve this problem, but most only deal with auditors in astatic position. They are based on the direct resolution of adaptive optimization methods, such as the Pressure Matching (PM) method.However, for moving users, these methods have a too high computation cost, making it impossible to apply them to a dynamic problem.The aim of this thesis is to develop a solution offering a level of complexity compatible with a dynamic control of Sound Zones, whilemaintening the performance of conventional methods. Under the assumption that displacements are slow, an iterative resolution of the PMproblem is proposed and assessed. The LMS, NLMS and APA algorithms are compared on the basis of free field simulations. The LMSmethod is the most advantageous in terms of complexity, but it suffers from a reproduction error. A memory effect limiting the reactivityof the algorithms is also highlighted. It is corrected by implementing a leaky variant (Variable Leaky LMS or VLLMS) introducing aforgetting factor.

Ultrasonic transducers are used in many fields of daily life, e.g. as parking aids or medical devices. To enable their usage also for mass applications small and low- cost transducers with high performance are required. Capacitive, micro-machined ultrasonic transducers (CMUT) offer the potential, for instance, to integrate compact ultrasonic sensor systems into mobile phones or as disposable transducer for diverse medical applications. This work is aimed at providing fundamentals for the future commercialization of CMUTs. It introduces novel methods for the acoustic simulation and characterization of CMUTs, which are still critical steps in the product development process. They allow an easy CMUT cell design for given application requirements. Based on a novel electromechanical model for CMUT elements, the device properties can be determined by impedance measurement already. Finally, an end-of-line test based on the electrical impedance of CMUTs demonstrates their potential for efficient mass production.

Ultrasonic transducers are used in many fields of daily life, e.g. as parking aids or medical devices. To enable their usage also for mass applications small and low- cost transducers with high performance are required. Capacitive, micro-machined ultrasonic transducers (CMUT) offer the potential, for instance, to integrate compact ultrasonic sensor systems into mobile phones or as disposable transducer for diverse medical applications. This work is aimed at providing fundamentals for the future commercialization of CMUTs. It introduces novel methods for the acoustic simulation and characterization of CMUTs, which are still critical steps in the product development process. They allow an easy CMUT cell design for given application requirements. Based on a novel electromechanical model for CMUT elements, the device properties can be determined by impedance measurement already. Finally, an end-of-line test based on the electrical impedance of CMUTs demonstrates their potential for efficient mass production.