As discussed in the previous chapter, hearing and vision are the two most important sensor inputs that humans have. Many parallels exist between visual signal processing and acoustic signal processing, but sound has unique properties – often complementary to those of visual signals. In fact, this is why nature gave animals both visual and acoustic sensors: to gather complementary and correlated information about the happenings in an environment. Many species use sound to detect danger, navigate, locate prey, and communicate. Virtually all physical phenomena – fire, rain, wind, surf, earthquake, and so on – produce unique sounds. Species of all kinds living on land, in the air, or in the sea have developed organs to produce specific sounds. In humans, these have evolved to produce singing and speech.

In this chapter, we introduce the basic properties of sound, sound production, and sound perception. More details of audio and audio processing are covered later in this book.