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Glossary [A-C]
Terminology of Sound
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Ambient Channel
A way of displaying sounds as coming from everywhere, i.e. all around the listener.  This is useful for background music or ambient sounds such as rain.
Echoless: producing or characterized by few or no echoes
Atmospheric Absorption
The attenuation of sounds as they propagate through a medium.  For example, in air the high frequency components of sound attenuate faster than the lower frequency components.
See Acoustetron above.
Audio Simulation
Naturally, sound is physically realized, from its creation, through propagation, to reception, as mechanical compression of media.  Media that are in contact with one another transfer this compression from one medium to the other.  As the compression spreads, energy is dissipated or absorbed, infinitely reducing the magnitude of the compression.  While sound gets most of its characteristic from the originating mechanical event, each propagation and transmission stage make subtle alterations to the sound.  "Audio simulation" is the simulation of all of these mechanical events through digital models (see Digital Models)
Aural Image
Audio signals that have been modified to appear to a human ear to originate from a specific point in 3D space.
The process of rendering audio by physically or mathematically modeling the sound field of a source in space in such a way as to simulate the binaural listening experience at any given position in the modeled space.
Binaural, immersive, interactive, real-time 3D audio technology by AuSIM, Inc.
Two audio tracks, one for each ear (as opposed to stereo, which is one for each speaker).  Binaural sounds are what we hear in everyday life.
Boresight Axis
Axis defined by the boresight direction (see boresight direction)
The headphone cup surrounds the pinnae. Aviation headsets are a good example of such devices.  Circumaural are not as accurately positioned as fitted intraural devices, but they are far better and more consistent than earbuds and supraural headphones.
Boresight Direction
Principal direction of aural emission of a sound source
Closed Headphones
Generally speaking, a distinction is made between open and closed headphones  With closed headphones, the ear is completely sealed off from outside noise (pressure chamber principle).  Closed headphones attenuate the physical aural world by 6 to 36 dB, depending on model.

Typical features of closed headphones are the acoustically sealed housing and the ring-shaped (circumaural) pads that completely surround the ear.  The sealing around the ear has a decisive influence on the sound reproduction of closed headphones.  If it is insufficient, the quality of the bass sounds will deteriorate.  For this reason, the contact pressure of closed headphones is higher than that of open headphones. Closed headphones are often used by sound engineers to allow them to concentrate on the music without disturbance from outside noise.

Generally speaking, open headphones are for augmented reality, while closed headphones are for virtual reality.
Contralateral Ear
The ear oppositely positioned in the body: used to describe a body part on the opposite side of the body or that acts in conjunction with such a part.
The world's first multi-source, real-time, digital localization system, built by Crystal River Engineering for NASA in 1987.
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