Communication Acoustics: An Introduction to Speech, Audio and Psychoacoustics

2 Physics of Sound

The word sound in English has two confusingly different meanings. It may refer to the physical phenomenon or to the subjective percept. The old philosophical dilemma ponders, ‘If a tree in the forest falls down and there is no observer, does it make a sound?’ Based on experimental evidence and by making a clear distinction between these two meanings, we may say that a falling tree causes a physical sound event that can be recorded and analysed every time, but it does not make any sound in the sense of an auditory perception if there is no subject to hear the event.

In this chapter, we look at the physical side of the concept of sound. Without a physical basis there can be no sound event; the emergence of sound requires a physical substrate, and its perception a physiological one. Although complicated in practice, the physics of sound has a basis that is well formulated mathematically and is thus a widely studied topic in science and engineering. We do not go deeply into physical acoustics here, but rather we present an overview of the most basic concepts necessary or helpful to understand communication by sound and voice. Finding more specialized textbooks and publications is easy, and this chapter includes references to many such sources for more information. This overview serves to refresh the memory of those who have already studied physical acoustics and as a starting point for those who have not.

2.1 Vibration and Wave Behaviour of Sound

Sound, ...