virtual acoustics

(engineering acoustics) Digitally processing sounds so that they appear to come from particular locations in three-dimensional space, with the goal of simulating the complex acoustic field experienced by a listener within a natural environment. Also known as auralization; three-dimensional sound.

The stimulation of the complex acoustic field experienced by a listener within an environment. The technology is also known as three-dimensional sound and auralization. Going beyond the simple left-right volume adjustment of normal stereo techniques, the goal is to process sounds so that they appear to come from particular locations in three-dimensional space. Although loudspeaker systems have been developed, much of the work in the field focuses on using headphones for playback and is the outgrowth of earlier analog techniques. For example, in binaural recording, the sound of an orchestra playing classical music is recorded through small microphones in the two imitation ear canals of an artificial or dummy head placed in the audience of a concert hall. When the recorded piece is played back over headphones, the listener passively experiences the illusion of hearing the violins on the left and the cellos on the right, along with all the associated echoes, resonances, and ambience of the original environment. Techniques use digital signal processing to synthesize the acoustical properties that people use to localize a sound source in space. Thus, they provide the flexibility of a kind of digital dummy head, allowing a more active experience in which a listener can both design and move around or interact with a simulated acoustic environment in real time.

The success of virtual acoustics is critically dependent on whether the acoustical cues used by humans to locate sounds have been adequately synthesized. There may be many cumulative effects on the sound as it makes its way to the eardrum, but all of these effects can be expressed as a single filtering operation much like the effects of a graphic equalizer in a stereo system. The exact nature of this filter can be measured by an experiment in which an impulse (a single, very short sound pulse or click) is produced by a loudspeaker at a particular location. The acoustic shaping by the two ears is then measured by recording the outputs of small probe microphones placed inside the ear canals of the individual or an artificial head. If the measurement of the two ears occurs simultaneously, the responses, when taken together as a pair of filters, include an estimate of the interaural differences as well. Thus, this technique makes it possible to measure all of the relevant spatial cues together for a given source location, for a given listener, and in a given room or environment. See also Equalizer; Psychoacoustics; Sound.