Speech and Audio Signal Processing: Processing and Perception of Speech and Music, Second Edition

CHAPTER 13

ROOM ACOUSTICS

13.1 INTRODUCTION

In previous chapters, we described some of the fundamentals of the acoustics of tubes and strings, using abstractions that we showed to be relevant to the production of audio signals in the human vocal tract and in some musical instruments. Once these signals leave their sources, however, they generally encounter boundaries that are at least partially reflective. Thus, a listener or a microphone receives a multipath version of the original source signal. Therefore, room acoustics are also a fundamental concern for many audio signal-processing applications. In this chapter, we discuss the effect of room boundaries on a sound wave, the resulting phenomenon of reverberation (i.e., the smearing of a source sound over time as a result of these boundary effects), and the effect of reverberation on speech intelligibility. As with many topics discussed in this book, this chapter can only serve as a brief introduction, with a practical focus on factors that affect the goals of audio signal processing.

13.2 SOUND WAVES

At atmospheric pressure and standard conditions of humidity, the speed of sound is

where T is the temperature of the air in degrees Celsius. At 20°C, the speed of sound is 343.4 m/s, or about 1127 ft/s, corresponding to a transmission ...