Preface

Spatial audio is a dynamic and rapidly evolving field, the consequence of being closely linked to advances in computer technology and digital signal processing. The democratisation of virtual reality hardware available as consumer devices has moved the field towards applications and further away from traditional laboratory research. This book, Advances in Fundamental and Applied Research on Spatial Audio, includes eight peer-reviewed chapters on this exciting area of research. The chapters are organised into three sections: "Acoustic Methodology," "Perception," and "Applications."

The first section addresses advances related to both loudspeaker and headphone presentation in the context of spatial audio. For loudspeaker reproduction, the first chapter in this section discusses requirements for 3D audio from the perspectives of physical modelling and output-based measurements, considering the special requirements for sound-field control and including new metrics that simplify the interpretation of loudspeaker properties at individual points, sound zones, and across the entire sound field. For headphone reproduction, the second chapter provides an overview of state-of-the-art methods for capturing personalised head-related transfer functions (HRTFs).

The second section addresses binaural spatial perception, considering its quantification, multimodal interactions, and the limitations of reverberation perception. The first chapter in this section presents a meta-analysis of raw data from several studies and discusses HRTF performance evaluation methods and metrics, highlighting issues in both the design of evaluation protocols and the selection of metrics for better comparisons between studies. The second chapter examines the influences of the presence and characteristics of acoustic and visual environments on the perceived distance and room size, employing an extra-aural headset and a semi-panoramic stereoscopic projection. The third chapter provides an overview of recent research on reverberation perception in a binaural surround-sound context, with a focus on how to enable more efficient reproduction of realistic sound scenes. Special emphasis is given to Ambisonics-based techniques and the effect of spatial resolution on the perceptual quality of binaural reproduction.

The third and final section focuses on applied research and includes three chapters. The first chapter presents a method for improved rendering of Ambisonic sound fields incorporating ear orientation under the term Bilateral Ambisonics, an Ambisonic representation of the sound field formulated at both ears. The second chapter examines, in the context of modern automotive acoustic and audio environments, the fundamental and practical aspects of acoustic echo cancellation, noise reduction, reverberation reduction, and beamforming signal processing methods, with the aim of spatially enhancing signals and creating listening zones in cars. The final chapter addresses several case studies conducted in various settings, comparing the experiences of orchestra conductors and instrumentalists monitoring their performances with binaural and stereo headphone-based sound reproduction.

We gratefully acknowledge the support of the SONICOM project (www.sonicom.eu), funded under the European Union's Horizon 2020 research and innovation program under grant agreement No. 101017743, and the Aural Assessment By means of Binaural Algorithms (AABBA) working group in the preparation of this anthology.
