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Why is 0 dB used as the reference level on an audiogram?

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In the context of clinical audiology, the 0 dB reference level on an audiogram—often referred to as audiometric zero—represents the median hearing threshold for young, healthy adults under favorable, noise-free laboratory conditions.12

Established as an international standard in 1964, this baseline provides a consistent reference point for measuring hearing sensitivity. Because individual hearing thresholds vary, the range of normal hearing is generally considered to be within ±20 dB of this zero line. When a person's hearing threshold is plotted on an audiogram, the value indicates how many decibels above this standardized normal threshold the individual's hearing level is for a specific frequency.21