Stereophonic sound

Stereophonic sound, commonly called stereo, is the reproduction of sound, using two independent audio channels, through a pair of widely separated speaker systems, in such a way as to create a pleasant and natural impression of sound heard from various directions as in natural hearing.

Various methods of stereo recording

X-Y technique is intensity sterophony

Here there are two directional microphones at the same place, and typically pointing at an angle 90° or more to each other. A stereo effect is achieved simply through sound pressure level differences of the sound entering each microphone. Due to the lack of time-of-arrival stereo information, the stereo effect in X-Y recordings is less realistic than a stereo recording.

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Intensity stereo is an unfortunate linguistic misnomer which has come to mean the recording of stereophonic signals that are distinguished only by level differences. These "level differences" have been called "intensity" differences, but sound intensity is a specifically defined quantity and cannot be sensed by a simple microphone, nor would it be valuable in music recording if it could. Our ear drums are only sensitive to the sound pressure, like microphones.

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A-B technique is time-of-arrival sterophony

This uses two omnidirectional microphones some distance apart, so capturing time-of-arrival stereo information as well as some level (amplitude) difference information.

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Near-coincident technique is mixed stereophony

e.g. the ORTF stereo technique of the Office de Radiodiffusion Télévision Française = Radio France, calls for a pair of cardioid microphones placed 17 cm apart at an angle of 110 degrees. In the NOS stereo technique of the Nederlandse Omroep Stichting = Holland Radio, the angle is 90 degrees and the distance is 30 cm, so capturing time-of-arrival stereo information as well as level information. Even the spacing of 17 cm has nothing to do with human ear distance. The developed signals are made for stereo loudspeakers and not for ear phones.

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