• The quality of a sound pressure level being sufficient to be detected by human ears, that is, being of 0 decibels or greater. Since hearing acuity varies considerably from human to human, it has been internationally agreed that a value of 20 micropascals is the equivalent of 0 decibels to a person with good hearing. Thus, any sound pressure level equal to or greater than 0 decibels is considered audible. Before pain sets in, a person with good hearing can listen at 120 decibels, or 20 pascals, which is a trillion times louder than 0 decibels.

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