4. How We Perceive Sound

Auditory scene analysis is the process by which we perceive the distance, direction, loudness, pitch, and tone of many individual sounds simultaneously.

Analyzing auditory scenes is a complex human ability. Our environment surrounds us with constant sound. Even the smallest vibrations and echoes help us to identify our surrounding area. Sounds in a small area produce fewer echoes than sounds in a large area.

The simplest way in which we can determine the location of the source of a sound is by comparing the intensity of the sound in our ears. We can further pinpoint a sound's position in space by using the ear-body-brain combination to decode localization cues. Localization cues are divided into two categories.

There are dynamic cues, such as vision, reverberation, early echo response, and head motion. There are also static cues: shoulder echo, pinna response, head shadow, and interaural time difference. The pinna response refers to the fact that the pinna filters out certain frequencies of sound depending on the direction from which the sound comes. Sounds coming from the back may, for example, have their 1000 Hz frequencies filtered out by the back of the pinna. We perceive this as a subtle change in the quality of a sound, but we are used to having sounds coming from behind us filtered in this way.

Because of this we are able to use this change in quality as a way to determine if the sound comes from in front of us, below us, behind us, or over us. Newer technologies, such as 3D sound and other advances in the digital era, are refining the process further. These recordings, however, are still crude imitations of the process by which the human ear receives and understands sound.

 

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