Microphone array processing for parametric spatial audio techniques

Abstract

Reproduction of spatial properties of recorded sound scenes is increasingly recognised as a crucial element of all emerging immersive applications, with domestic or cinema-oriented audiovisual reproduction for entertainment, telepresence and immersive teleconferencing, and augmented and virtual reality being key examples. Such applications benefit from a general spatial audio processing framework, being able to exploit spatial information from a variety of recording formats in order to reproduce the original sound scene in a perceptually transparent way. Directional Audio Coding (DirAC) is a recent parametric spatial sound reproduction method that fulfils many of the requirements of such a framework. It is based on a universal 3D audio format known as B-format and achieves flexible and effective perceptual reproduction for loudspeakers or headphones. Part of this work focuses on the model of DirAC and aims to extend it. Firstly, it is shown that by taking into account information of the four-channel recording array that generates the B-format signals, it is possible to improve both analysis of the sound scene and reproduction. Secondly, these findings are generalised for various recording configurations. A further generalisation of DirAC is attempted in a spatial transform domain, the spherical harmonic domain (SHD), with higher-order B-format signals. Formulating the DirAC model in the SHD combines the perceptual effectiveness of DirAC with the increased resolution of higher-order B-format and overcomes most limitations of traditional DirAC. Some novel applications of parametric processing of spatial sound are demonstrated for sound and music engineering. The first shows the potential of modifying the spatial information in the recording for creative manipulation of sound scenes, while the second shows improvement of music reproduction captured with established surround recording techniques.The effectiveness of parametric techniques in conveying distance and externalisation cues over headphones, led to research in controlling the perceived distance using loudspeakers in a room. This is achieved by manipulating the direct-to-reverberant energy ratio using a compact loudspeaker array with a variable directivity pattern. Lastly, apart from reproduction of recorded sound scenes, auralisation of the spatial properties of acoustical spaces are of interest. We demonstrate that this problem is well-suited to parametric spatial analysis. The nature of room impulse responses captured with a large microphone array allows very high-resolution approaches, and such approaches for detection and localisation of multiple reflections in a single short observation window are applied and compared.