In Chap. 3 , we examined the waveform of a pure tone, a type of sound that has a single frequency with periodic variations, such as the sound made by a tuning fork. However, as is well known, such sounds are not natural and cannot be heard in everyday life. Most sounds we usually hear are complex tones (complex sound) based on pure tones. The sounds of musical instruments create complex tones, a mixture of various pure tones, although it may not seem so.