DAFX: Digital Audio Effects, Second Edition

5.6 Reverberation

5.6.1 Basics of Room Acoustics

Most of the techniques presented in previous sections have concentrated on reproducing one sound source in a free field from a certain direction. However, in a real space reverberation is always present. Reverberation is composed of reflections which are delayed and attenuated copies of the direct sound. The frequency content of each reflection is also modified due to the directivity of the sound source and due to the material absorption of reflecting surfaces.

The most important concept in room acoustics is an impulse response which describes the acoustics of a room from a static sound source to a listening position. Engineers often divide the impulse response into three parts, the direct sound, early reflections and late reverberation. This division is illustrated with a simulated impulse response in Figure 5.11. The direct sound is the sound reaching the listener first. The early reflections are the first reflections that are not perceived separately as human hearing integrates them with the direct sound. Although their individual directions are not perceived due to the precedence effect, they contribute to the perception of the sound color and the size of the sound source, as well as the size of the room. Late reverberation is considered after a time moment, which is sometimes called the mixing time, when the reflection density is so high that individual reflections cannot be seen in the response. Late reverberation gives cues ...