In the usual stereo audio presentation, a partial sound stage consisting primarily of the front elements of the sound stage is created by two channels, either sampled from several microphones set in the original sound field or more often by a mixdown of many microphones placed both in proximity to the performers and out in the hall to capture the ambience. The information presented by the two channels, in either case, is a small fraction of the information in the original sound field. Additionally, this fraction is presented to the front of the listener. The presentation does not create an envelopment experience, where one is immersed in the original sound field, as the information is not present. While some processors mimic the effect, such effects are not based on the actual venue but rather on some hypothetical model of a venue. : In holographic or auralized two-channel presentation, a presumed human head-related transfer function (HRTF) is used to create an impression of sound arising from other than the front of the listener. This works well in headphones or with interaural cancellation for one listener facing directly ahead and on the central axis between the loudspeakers. This method can, with some difficulty, produce an immersive effect for one point in the sound field, assuming that the subject maintains the proper head position, and the subject's head has an HRTF like that of the presumed functions. The ultimate form of this is, of course, binaural recording, where an actual head model is used to capture the information for one head location. : Beyond two-channel presentation, one can think of analytically capturing an original sound field to some degree of accuracy. This would require the use of many channels, perhaps placed in a sphere about the listener's head in the simplest form, requiring very high data rates (1000 to : 10 000 channels, perhaps) and creating a very high probability of influencing the sound field in the space with the microphones and the supporting mechanisms. As a result this technique is currently infeasible, and is likely to remain infeasible, for basic physical reasons as well as data-rate reasons, and actual analytic capture of the spatial aspects of a sound field in this fashion is unlikely.:
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