The energy source: reflected light; emitted sound

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An introduction to auditory objects, events, figures, images and scenes

There is an important difference between visual objects and auditory objects that arises at a very basic level: The light that gives rise to a visual object is typically reflected from the surface of a physical object; the light source is typically diffuse, broadband, and of secondary importance to us in the generation of the visual object. It is the pattern of absorption and reflection on the surface of the physical object that is important for determining the pattern of light that reaches the eye. The sounds that gives rise to the auditory object of particular interest are typically emitted by the object rather than reflected, and the sound is typically emitted from a restricted part of the surface of the object, that does not indicate how the sound was generated. The pattern in the sound is largely determined by the shape and structure of resonating objects inside the visible object, resonating objects which are themselves not visible, and not readily imaginable for listeners without specialist knowledge of acoustics. It is this difference in the source of the energy that gives rise to the pattern that eventually leads to the perception that leads us to refer to sound sources as “sources” rather than objects, and for this reason, I have used source, rather than object, as the ultimate base of the expression on the physical side of the equation in the acoustic/auditory case.

There are light sources that function as physical objects, emitting photons rather than reflecting them, and there are a few sources, such as the sun, where some of the photons actually come from deep within the physical object. But these are not usually the sources we mean when talking about visual objects; the typical visual object arises from reflected light.

Physical objects do reflect sound from their surfaces, much as they reflect light, and the reflected sound contains some information about the physical object. However, this reflected sound …

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