This chapter offers some of the basic principles of audio and acoustics, such as the nature of sound in the air and in electrical form, and some units, measurements, and laws. The important characteristic of sounds which have a definite pitch is that they are repetitive: that is, the waveform. All such waveforms can be broken down into a series of components known as harmonics, using a mathematical process called Fourier analysis. A white noise signal’s spectrum is flat, when averaged over a period of time, right across the audio-frequency range. White noise has equal energy for a given bandwidth, whereas another type of noise, known as pink noise, has equal energy per octave. At low frequencies where the wavelength is comparable with the dimensions of the room, it is necessary to consider other factors, since the room behaves more as a complex resonator, having certain frequencies at which strong pressure peaks and dips are set up in various locations.