Virtual Acoustic Space

Virtual Acoustic Space

Virtual Acoustic Space (VAS), also known as Virtual Auditory Space, is a technique in which sounds presented over headphones appear to originate from any desired direction in space. The illusion of a virtual sound source outside the listener's head is created.

Sound localization cues generate an externalized percept

When one listens to sounds over headphones (in what is known as the "closed field") the sound source appears to arise from center of the head. On the other hand, under normal, so-called free-field, listening conditions sounds are perceived as being externalized. The direction of a sound in space (see sound localization) is determined by the brain when it analyses the interaction of incoming sound with head and external ears. A sound arising to one side reaches the near ear before the far ear (creating an interaural time difference, ITD), and will also be louder at the near ear ear (creating an interaural intensity difference, IID). These binaural cues allow sounds to be lateralized. Although conventional stereo headphone signals make used of ILDs (not ITDs) the sound is not perceived as being externalized.

The perception of an externalized sound source is due to the frequency and direction-dependent filtering of the pinna] which makes up the external ear structure. Unlike ILDs and ITDs, these spectral localization cues are generated monaurally. The same sound presented from different directions will produce at the eardrum a different pattern of peaks and notches across frequency. The pattern of these monaural spectral cues is different for different listeners. Spectral cues are vital for making elevation judgments and distinguishing if a sound arose from in front or behind the listener. They are also vital for creating the illusion of an externalized sound source. Since only ILDs are present in stereo recordings, the lack of spectral cues means that the sound is not perceived as being externalized. The easiest way of re-creating this illusion is to make a recording using two microphones placed inside a dummy human head. Playing back the recording via headphones will create the illusion of an externalized sound source.

VAS creates the perception of an externalized sound source

VAS is effectively the same as the dummy head technique except that it uses digital signal processing. The VAS technique involves two stages: recording the transfer function of the head and playing back the sounds through a VAS filter. 1) The ILDs, ITDs, and spectral cues make up what is known as the Head Related Transfer Function which defines how the head and outer ears filter incoming sound. The HRTF can be measured by placing miniature probe microphones into the subject's ears and recording the impulse responses to broad-band sounds presented from a range of directions in space. Since head size and outer ear shape vary between listeners a more accurate effect can be created by individualizing the VAS filters in this way. However, a foreign HRTF or an average HRTF taken over many listeners is still very effective.

2) The bank of HRTF impulse responses are now be converted into a filter bank of some sort (e.g. minimum phase filters). Any desired sound can now be convolved with one of these filters and played to a listener over headphones. This creates the perception of an externalised sound source. This approach has obvious advantages over the "dummy head technique", most notably the fact that once the filter bank has been obtained it can be applied to any desired sound source.

Uses for VAS in scienceIn addition to obvious uses in the home entertainment market, VAS has been used to study how the brain processes sound source location. For example, at the Oxford Auditory Neuroscience Lab ( scientists have presented VAS-filtered sounds whilst recording from neurons in the auditory cortex and mid-brain.

ee also

* Sound localization

External links

* is an audio file containing a VAS recording.



Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Space music — Space music, also spelled spacemusic, is an umbrella term used to describe music that evokes a feeling of contemplative spaciousness. In fact, almost any music with a slow pace and space creating sound images could be called spacemusic. Stephen… …   Wikipedia

  • Acoustic transportation — is a process that was developed by John Maxwell Hobbs and David Hykes.In 1995, Hobbs and Hykes worked together with Lauren Dyer Amazeen, Michel Redolphi and Luc Martinez to created the Virtual Abbey. The Virtual Abbey was the first realization of …   Wikipedia

  • Virtual Orchestra — is a term used to identify a variety of different types of technology and art forms. Most commonly used to refer to orchestral simulation, either for pre recorded or live environments, it also has been used to describe other activities, such as… …   Wikipedia

  • Musique en réseau — Un concert de musique en réseau ou de télémusique consiste en une ou des interactions en temps réel, en direct et à distance, assurées par un réseau informatique (et télématique) qui permet aux musiciens répartis dans différents lieux distants de …   Wikipédia en Français

  • Wave field synthesis — (WFS) is a spatial audio rendering technique, characterized by creation of virtual acoustic environments. It produces artificial wave fronts synthesized by a large number of individually driven speakers. Such wave fronts seem to originate from a… …   Wikipedia

  • Convolution reverb — In audio signal processing, convolution reverb is a process for digitally simulating the reverberation of a physical or virtual space. It is based on the mathematical convolution operation, and uses a pre recorded audio sample of the impulse… …   Wikipedia

  • Sound localization — refers to a listener s ability to identify the location or origin of a detected sound in direction and distance. It may also refer to the methods in acoustical engineering to simulate the placement of an auditory cue in a virtual 3D space (see… …   Wikipedia

  • LARES — For the flag carrier airline of Romania, see TAROM. LARES is an electronic sound enhancement system that uses microprocessors to control multiple loudspeakers and microphones placed around a performance space for the purpose of providing active… …   Wikipedia

  • performing arts — arts or skills that require public performance, as acting, singing, or dancing. [1945 50] * * * ▪ 2009 Introduction Music Classical.       The last vestiges of the Cold War seemed to thaw for a moment on Feb. 26, 2008, when the unfamiliar strains …   Universalium

  • microscope — /muy kreuh skohp /, n. 1. an optical instrument having a magnifying lens or a combination of lenses for inspecting objects too small to be seen or too small to be seen distinctly and in detail by the unaided eye. 2. (cap.) Astron. the… …   Universalium