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Glossary [S-V] Terminology of Sound

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		Sample Rate The number of samples per second at which a sound is processed (usually ranges from 8 kHz to 192 kHz NOTE: CD quality is 44.1kHz, or 44,100 samples per second.
		Shadowing The reduction in size or intensity of a sound wave due to decreasing transmissivity of sound waves by human head tissue versus air.
		Sound Source Refers to an object in 3D space that emits sound. The actual sound signal that it sends out can be a live signal, a wave file, or any other audio signal. A 3D sound device is often rated on how many different sources it can independently position at any one time. Realistic sound spaces can be created with as few as four concurrent sources; very complex spaces can have dozens of separate sounds at a time
		Spatialization The process of modifying an audio signal for the purpose of making it appear to a human ear to originate from a specific point in 3D space.
		Speaker Arrays An installation of multiple speakers in a certain pattern, usually designed to create a sound field within the space defined by the speakers. Examples are stereo speakers, or quadraphonic speakers.
		Stereo/Stereophonic Refers to two audio signals, usually rendered on two separate speakers. Stereo sounds appear to originate from somewhere between the two speakers, or between the ears of a listener in the case of headphones.
		Supraural Headphones where the transducers rest on top of the pinnae (ear lobe). Airline passenger headphones are an example of such devices. Supraural headphones are the worst for 3D audio, because positional placement over the ear is very inconsistent. Supraural-closed headphones actually do exist; the most popular broadcast headset today is the Sennheiser HEC-25 which is supraural (comfortable) and closed (to the crowd noise).
		Surfaces Sounds not only travel to a pair of ears on a direct path, but they also bounce off objects in the world. Most natural listening environments contain at least a sound reflecting ground plane, such as a floor. Therefore, reflecting objects are necessary to make virtual environments sound natural and realistic. They help listeners navigate and enhance the overall effect of immersion in a virtual environment. Almost as important as reflections, is the absence of a reflection. For example, the brain can tell the change in a sound space when a reflection is removed by opening a door or a window.
		Sweet Spot The location where a listener has to be placed to get the optimal effect when listening to a specific speaker setup.
		Transmission Loss Sounds get absorbed as they travel through objects such as walls (similar to atmospheric absorption in the case of traveling through a medium). Transmission loss models are needed to realistically simulate sounds outside a window or in the next room.
		Update Rate The number of times that a specific instance of a sound space is re-computed and updated per second. Each time any object moves (most often the listener), the space needs to be updated. The higher the update rate, the faster objects can move without creating audio artifacts, such as clicking. Audio update rates generally range from a minimum of 20Hz to 100Hz. Video update rates are usually in the same range (TV signals are updated at 25 OR 30Hz).

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