binaural

Binaural describes something involving two ears. In acoustics and audio, binaural audio refers to sound recordings or processing designed to create a sense of spatial position when heard over headphones, as if the sound surrounds the listener.

Conceptually, binaural hearing relies on cues that the brain uses to locate sound sources. When sound arrives at the two ears at slightly different times and levels, the brain uses interaural time differences (ITD) and interaural level differences (ILD) together with spectral cues shaped by the head and outer ears, called head-related transfer functions, to infer direction and distance.

Binaural recording and synthesis emulate these cues. Recordings are usually captured with two microphones placed at or near ear positions or with a dummy head; playback requires headphones to preserve the spatial cues. Binaural audio can produce a more lifelike sense of space than standard stereo, especially for near-field sounds.

Binaural beats are a related phenomenon in which two tones with close frequencies are played to each ear separately, producing the perception of a beating tone corresponding to the frequency difference. Proponents claim effects on mood or focus, but rigorous evidence is limited, and conclusions remain unsettled. Some devices advise caution for individuals with epilepsy or migraine.

Applications include music production, virtual reality, 3D audio for films, hearing research, and assistive listening studies. Limitations include reduced realism when not using headphones and the influence of individual ear anatomy on perceived direction.