Digital Audio Signal Processing, 3rd Edition

Chapter 7Room Simulation

U. Zölzer P. Nowak and P. Bhattacharya

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.

7.1 Basics

7.1.1 Room Acoustics

The room impulse response between two points in a room can be classified as shown in Fig. 7.1. 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 of 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 according to

(7.1)

The geometry of the room also determines the eigenfrequencies of a three‐dimensional rectangular room:

(7.2)

with

For larger rooms, the eigenfrequencies start from very low frequencies. ...