This chapter covers the details of a sound wave and explores some of the language of audio. Sound is a vibration or a series of vibrations that move through the air. Anything that creates the vibrations, or waves, is referred to as the source. The source can be a string, a bell, a voice, or anything that generates a vibration within our hearing range. The chapter deals with the seven characteristics of a sound wave: amplitude, frequency, phase, velocity, wavelength, harmonics, and envelope. Waveform defines the size and shape of a sound wave. Noise is a hum, a hiss, or a variety of extraneous sounds that accompany a sound wave when it is mixed or recorded. Distortion, unlike noise, is caused by setting or recording levels too hot, pushing vacuum tubes, or by bad electronics.