collection of mono and/or true stereo recordings. Modern popular music, in particular, is usually recorded using close miking techniques, which artificially separate signals into several tracks. The individual tracks (of which there may be hundreds) are then "mixed down" into a two-channel recording. The audio engineers determine where each track will be placed in the stereo "image", by using various techniques that may vary from very simple (such as "left-right" panning controls) to more sophisticated and extensively based on psychoacoustic research (such as channel equalization, mid-side processing, and the use of delay to exploit the precedence effect). The end product using this process often bears little or no resemblance to the actual physical and spatial relationship of the musicians at the time of the original performance; indeed, it is not uncommon for different tracks of the same song to be recorded at different times (and even in different studios) and then mixed into a final two-channel recording for commercial release. Classical music recordings are a notable exception. They are more likely to be recorded without having tracks dubbed in later as in pop recordings, so that the actual physical and spatial relationship of the musicians at the time of the original performance can be preserved on the recording. Balance Balance can mean the amount of signal from each channel reproduced in a stereo audio recording. Typically, a balance control in its center position will have 0 dB of gain for both channels and will attenuate one channel as the control is turned, leaving the other channel at 0 dB. See also 3D audio effect 5.1 surround sound Acoustic location Acoustic source localization Ambisonics – generalized MS-Stereo to three dimensions Crossfeed Duophonic sound Joint stereo Sound localization Stereo photography Subwoofer (stereo separation) Summing localization Sweet spot (acoustics) Wave field synthesis – the physical reconstruction of the spatial sonic field Notes References Sound recording Music technology