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Virtual surround


Virtual surround is an audio system that attempts to create the perception that there are many more sources of sound than are actually present. In order to achieve this, it is necessary to devise some means of tricking the human auditory system into thinking that a sound is coming from somewhere that it is not. Most recent examples of such systems are designed to simulate the true (physical) surround sound experience using one, two or three loudspeakers. Such systems are popular among consumers who want to enjoy the experience of surround sound without the large number of speakers that are traditionally required to do so. The Nintendo DS and 3DS can produce virtual surround sound.

A virtual surround system must provide a means for 2-dimensional imaging of sound, using some properties of the human auditory system. The way that the auditory system localises a sound source is a topic that is studied in the field of psychoacoustics. Thus, virtual surround systems use knowledge of psychoacoustics to "trick" the listener. There are several ways in which this has been attempted.

Some methods use knowledge of head-related transfer function (HRTF). With an appropriate HRTF the signals required at the eardrums for the listener to perceive sound from any direction can be calculated. These signals are then recreated at the eardrum using either headphones or a crosstalk calculation method . For an application of this method, see ISVR, Virtual Acoustics And Audio Engineering. The disadvantage of this approach is that it is very difficult to get these systems to work for more than one listener at a time.

Some virtual surround systems work by directing a strong beam of sound to reflect off the walls of a room so that the listener hears the reflection at a higher level than the sound directly from the loudspeaker. One example of this technology is a commercially available Digital Sound Projector by Cambridge Mechatronics (formerly 1 Ltd). It employs 40 micro drivers and 2 woofers as well as projection technology to control the direction of the sound. The micro drivers' sound is focused into groups of "beams" that reflect off the room's walls. The center channel's sound is projected directly to the listening position. Another example is S-Logic marketed by a German headphones manufacturer Ultrasone. With this technology (which may also be considered a hybrid of HRTF and reflection-based methods), decentralized transducer positioning is used to spread sound over the outer ear in an attempt to mimic sound heard over speakers.


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