DAFX: Digital Audio Effects, Second Edition

5.1 Introduction

A listener is capable of sensing his surroundings in some degree using only hearing, for example directions, distances, and spatial extents of sound sources, and also some characteristics of the rooms. This information is obtained by comparing the sound signals in ear canals to a set of spatial cues, used by the brain. Understanding the cues used by the hearing system helps the audio engineer to introduce some artificial features in the sound material in order to project the sound events in space. In the first half of this chapter, the most important techniques for sound projection are described, both for individual listeners using headphones and for an audience listening through a set of loudspeakers.

In natural listening conditions, sounds propagate from a source to the listener and during this trip they are widely modified by the environment. Therefore, there are some spatial effects imposed by the physical and geometric characteristics of the environment on the sound signals arriving to the listener's ears. Generally speaking, we call reverberation the kind of processing operated by the environment. The second half of this chapter illustrates this kind of effect and describes audio-processing techniques that have been devised to imitate and extend the reverberation that occurs in nature.

The importance of space has been largely emphasized in electroacoustic compositions, with the result that sophisticated spatial orchestrations often result in poor musical ...