Background

Our hearing is, along with our sight, a most important condition for communication. We rely on it perpetually every day when we, consciously or subconsciously, process all the information that is being transmitted by our surroundings, such as language, music or the sounds conveyed by ourselves. Our ability to determine the location of a sound refering to our own location is highly developed.
The technological capacity to reproduce sound has in many ways influenced our perception of sound. We have become used to hearing mono or stereo reproductions, recordings that do not allow for a genuine perception of space and distance. In recent years, surround sound has been launched, but even though this reproduction of sound conveys more spaciousness, it is still only a few directions and distances that can be represented this way.

Genuine 3D Sound is:
The ability to perceptually position a virtual sound source in any direction at any distance relative to the listener.

This is a very strict definition, which is very difficult to conform to. But at least the technology must be able to position a virtual sound source in all 3 dimensions to be called 3D Sound. Not necessarily all possible positions.

The most convincing method of reproducing a natural acoustical environment is performed using binaural technology, or the so-called "Dummy-Head technique". Dummy-Head is recording the sound by means of a set of microphones placed in the dummy's ears. These microphones pick up sound and intercept the change of pressure in the ear, in the exact same manner as that of a normal human ear.

Thus human hearing is being simulated. If the recording is then played via headphones, into the ears of a listener, the recording will appear to be three-dimensional. The listener can determine the position, the direction and the distance of the sound as accurately as if he/she had been present during the recording.

Instead of binaural recordings the sound can be synthesized. This is done by filtering a single channel audio signal with a filter that corresponds to the transformation that the human body and ears impose on a sound field reaching the eardrums. The filter characteristics are functions of direction and distance to the sound source.

Binaural sound reproduction can be done both via headphones or loudspeakers using crosstalk cancellation. The latter method is however not as accurate as the former.