3.1 Introduction

Similarly to the way humans perceive a visual image, humans are also able to perceive an auditory spatial image. The different objects which are part of the auditory spatial image are denoted auditory objects. For example, if a listener listens to a musical performance, the auditory objects are the different instruments which are playing. In most listening situations, the perceived directions of auditory objects correspond well to the directions of the physical sound sources emitting the sounds that are associated with the corresponding auditory objects. This is a necessity in order that the perceived auditory spatial image corresponds to the physical surroundings of a listener.

Figure 3.1 illustrates the perception of the auditory spatial image for a listener being in a performance with three sound sources in a room (left). For each source an auditory object is perceived (1 in Figure 3.1) with a specific position and width. The frontal auditory spatial image has also a total extent (2 in Figure 3.1) which is not necessarily directly associated with the auditory objects. The impression of being within the sound field is denoted listener envelopment (3 in Figure 3.1). The different attributes of the auditory spatial image, auditory object location/width and listener envelopment, have been discussed by Rumsey [228] in the context of spatial quality evaluation.

The chapter is organized as follows. A description of the physiology of the human auditory system is followed by an introduction of spatial hearing phenomena. The important case of spatial hearing in rooms is treated in detail. Limitations of the auditory system are described and a model is presented which attempts to explain the remarkable properties of the human auditory system in terms of perceiving complex auditory spatial images given a mix of source signals and reflections at the ear entrances. The chapter is concluded with a discussion on how the described spatial hearing knowledge relates to and enables spatial audio processing and coding.