Attempts have been made to process audio input signals so as to place them in a perceived three-dimensional sound space. It has been assumed that to place a sound behind a subject for example, that this would require a source of sound (i.e. a loudspeaker) to be placed behind a subject. This logically implies that for three-dimensional sound to exist, complex speaker systems must be created with loudspeakers above and below the plane of the ears of the listener. Clearly, this is not a satisfactory solution, even for highly specified cinemas for example and therefore practical deployment of such systems has only existed in extreme environments with very specialised venues.
Models have been constructed based upon attempting to hear what the ears hear. For example, experimentation has been performed using a standard dummy head in which the head has microphones mounted where each ear canal would normally sit. Experimentation has then been conducted in which many samples may be made of sounds from many positions. From this, it was possible to produce a head related transfer function, which is then in turn used to process sounds as though they had originated from certain desired positions. However, to date, the results have been less than ideal.