Stereophonic Sound

Stereophonic Sound uses two or more related channels to reproduce direction and spatial relationships. In everyday use, stereo usually means two-channel left-right reproduction: two speakers in front of the listener form a sound base, and differences in level, timing, and phase between left and right place images between or near the speakers.

Two channels do not necessarily mean stereo. Identical left and right signals are dual mono; two unrelated programs on each channel also lack a shared sound field. Stereo presentation exists only when channels are related to the same program to build spatial relationships. Recording may use paired microphones directly or mix multitrack material to left and right through panning, level, delay, and reverb.

Headphones deliver left and right signals directly to each ear, unlike frontal speaker playback with crosstalk and different directional conditions. Conventional speaker stereo on headphones may create in-head imaging; binaural recordings use head and pinna cues for headphone playback. Both use two channels but assume different production contexts.

Matrix surround can encode additional information into compatible two-channel stereo and decode it at playback from phase relationships; this does not change the fact that only two discrete channels exist on the carrier. A 2.0 label usually means two full-range channels without a separate LFE; the label alone cannot determine whether the recording is true stereo, dual mono, or a downmix from multichannel.