stereophonic

Stereophonic sound, or stereophony, is a method of sound reproduction that uses two or more independent audio channels to create the impression of a multi-directional sound field. By presenting different signals to the left and right channels, listeners perceive sound as coming from various directions around them rather than from a single point source.

The effect relies on interaural level differences, timing differences, and phase and spectral cues that the auditory system interprets as location. Techniques such as panning place sounds left or right in the stereo image, while microphone arrays and mixing choices shape the overall depth and width of the sound. Head-related transfer functions influence localization when listening over headphones.

History: British engineer Alan Blumlein developed a two-channel recording concept and filed a patent for stereophony in 1931. Practical adoption followed in the mid-20th century, with stereo music released on vinyl records in the late 1950s and stereo sound used in cinema and broadcasting. The term stereophony describes the approach, while stereo describes the common two-channel format.

In modern practice, stereo systems use two channels labeled left and right connected to two loudspeakers or to headphones. Many formats preserve mono compatibility by ensuring that a single-channel mix still yields a coherent result when summed. Although multichannel formats such as surround sound exist, stereo remains the standard for most music and everyday listening.

See also: binaural recording, stereo imaging, panning, surround sound.