Digital Audio Signal Processing, Second Edition

Chapter 6

Room Simulation

Room simulation artificially reproduces the acoustics of a room. The foundations of room acoustics are found in [Cre78, Kut91]. Room simulation is mainly used for post-processing signals in which a microphone is located in the vicinity of an instrument or a voice. The direct signal, without additional room impression, is mapped to a certain acoustical room, for example a concert hall or a church. In terms of signal processing, the post-processing of an audio signal with room simulation corresponds to the convolution of the audio signal with a room impulse response.

6.1 Basics

6.1.1 Room Acoustics

The room impulse response between two points in a room can be classified as shown in Fig. 6.1. The impulse response consists of the direct signal, early reflections (from walls) and subsequent reverberation. The number of early reflections continuously increases with time and leads to a random signal with exponential decay called subsequent reverberation. The reverberation time (decrease in sound pressure level by 60 dB) can be calculated, using the geometry of the room and the partial areas that absorb sound in the room, from

where T₆₀ is the reverberation time (in s), V the volume of the room (m³), S_n the partial areas (m²) and α_n the absorption coefficient of partial area S_n.

The geometry of the room also determines the eigenfrequencies of a three-dimensional ...