Evaluation of the accuracy of measurements performed by a spherical array of microphones

This Master’s thesis consists in evaluating a spherical microphone array developed in a previous project, which will be referred to later, that aimed to extract 3D Room Impulse Responses with a measurement system composed of the referred microphone, among other tools. We will focus on the accuracy of localization of the sound as a direct continuation of the previous work. It could be considered as the main application of this system, hence it is important to emphasize the need of this evaluation. The measurement system consists of a spherical antenna containing 16 microphones, two cards with 8 channels each and the associated signal treatment. The current aim is to evaluate the precision provided by the system, which is evaluated in several situations. Different acoustics measurements have been taken in an anechoic room and also in a reverberant room. Adobe Audition and the Matlab software are used in order to process the information which is provided by the measurement system

Spatial dissection of a soundfield using spherical harmonic decomposition

A real-world soundfield is often contributed by multiple desired and undesired sound sources. The performance of many acoustic systems such as automatic speech recognition, audio surveillance, and teleconference relies on its ability to extract the desired sound components in such a mixed environment. The existing solutions to the above problem are constrained by various fundamental limitations and require to enforce different priors depending on the acoustic condition such as reverberation and spatial distribution of sound sources. With the growing emphasis and integration of audio applications in diverse technologies such as smart home and virtual reality appliances, it is imperative to advance the source separation technology in order to overcome the limitations of the traditional approaches. To that end, we exploit the harmonic decomposition model to dissect a mixed soundfield into its underlying desired and undesired components based on source and signal characteristics. By analysing the spatial projection of a soundfield, we achieve multiple outcomes such as (i) soundfield separation with respect to distinct source regions, (ii) source separation in a mixed soundfield using modal coherence model, and (iii) direction of arrival (DOA) estimation of multiple overlapping sound sources through pattern recognition of the modal coherence of a soundfield. We first employ an array of higher order microphones for soundfield separation in order to reduce hardware requirement and implementation complexity. Subsequently, we develop novel mathematical models for modal coherence of noisy and reverberant soundfields that facilitate convenient ways for estimating DOA and power spectral densities leading to robust source separation algorithms. The modal domain approach to the soundfield/source separation allows us to circumvent several practical limitations of the existing techniques and enhance the performance and robustness of the system. The proposed methods are presented with several practical applications and performance evaluations using simulated and real-life dataset