Stereo sound refers to the creation of sound using multiple audio channels. It creates the illusion of sound coming from different directions and is much more effective at mimicking the experience of natural sound than single-channel, mono audio systems. Stereo sound is generally created with a network of at least two speakers located at a regular distance from a listener. These speakers may be as simple as a pair of headphones or as complicated as a vast theater sound system or concert rig. Most modern equipment capable of producing audio is designed primarily to employ stereo sound.
The human ear is designed to locate the source of sound in the environment. A single audio channel cannot fool the brain into believing that it can locate the source of a sound, but two or more sound channels can be combined in order to produce precisely that effect. In stereo sound, audio signals produced by different audio channels are designed and recorded so that the brain naturally interprets their combined signal as being sound from a particular source with a given spatial position.
Originally, stereo audio was recorded using two or more distinct microphones configured to record sounds at their positions, designed to correspond with the ideal locations of playback speakers. This method is still used, with additional permutations and equipment allowing for the recording of four or more audio channels for theater-quality sound. In many cases, however, a version of stereo sound is now produced digitally, with computer software modeling the sound from different positions. A similar process can be used to convert mono tracks to stereo sound and is sometimes used in the re-mastering of older audio tracks.
Most modern media systems are designed for stereo sound, though AM radio is one exception to this general trend. The technology does not support stereo very efficiently, leading to the dominance of talk radio in the AM spectrum. FM radio is generally broadcast in stereo because the medium effectively supports stereo signal transmission, making FM a more natural medium for music.
Stereo sound is not necessarily a better option than mono sound. In some environments, such as crowded dance clubs or large concerts, the difference between stereo and mono may not be noticeable to the audience. Small or inexpensive sound systems may also not be able to produce stereo sound that is notably better than mono. In most cases, stereo audio is configured to provide a sense of being in a real sound space but cannot be arranged so that most listeners could truly pinpoint the location of individual sounds.