8.1 Introduction

The synthesis process of virtual auditory scenes has been an ongoing research topic for many years. The aim of so-called binaural rendering systems is to evoke the illusion of one or more sound sources positioned around the listener using stereo headphones. The positions of the sound sources can preferably be modified in terms of the perceived azimuth, elevation and distance. More advanced systems also include room acoustic models to simulate the acoustical properties, such as reflecting walls within the virtual space.

Binaural rendering has benefits in the field of research, simulation and entertainment [237]. Especially in the field of entertainment, the virtual auditory scene should sound very compelling and ‘real’. In order to achieve such a realistic percept, several aspects have to be taken into account, such as the change in sound source positions with respect to head movement [197], room acoustic properties such as early reflections and late reverberation [236], and using system personalization to match the anthropometric properties of the individual user [198, 199, 276]. Because of the complex nature of current state-of-the-art systems, several concessions are required for feasible implementations (cf. [159]), especially if the number of sound sources that has to be rendered simultaneously is large.

Recent trends in consumer audio show a shift from stereo to multi-channel audio content, as well as a shift to solid state and mobile devices. These developments cause additional constraints on transmission and rendering systems. Firstly, the number of audio channels that has to be transmitted increases beyond two. The corresponding increase in transmission bandwidth for conventional, discrete-channel audio coders is often undesirable and sometimes even unavailable. Secondly, consumers often use headphones for audio rendering on a mobile device. To experience the benefit of multi-channel audio, a compelling binaural rendering system is required. This can be quite a challenge given the limited processing power and battery life of mobile devices.

In this chapter, a binaural rendering process will be described that exploits spatial audio coding techniques. The method is based on the analysis and synthesis of perceptually relevant parameters of a virtual auditory scene. The analysis and synthesis of these so-called binaural parameters is outlined in Sections 8.3 and 8.4; the integration of this method in the recently finalized MPEG Surround standard (cf. [138] and Chapter 6) for multi-channel audio compression is described in Section 8.5.