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11.21  hearing threshold; threshold of audibility. For a given listener and specified signal, the minimum (a) sound pressure level or (b) force level that is capable of evoking an auditory sensation in a specified proportion of trials. Sound reaching the ears from other sources is assumed to be negligible. Unit, decibel (dB).

Annotation 1          The characteristics of the test signal, the manner in which it is presented to the listener, and the place at which the sound pressure level or force level is measured should be specified.

Annotation 2          ANSI/ASA S3.21-2004 (R 2009), American National Standard Methods for Manual Pure-Tone Threshold Audiometry recommends that a hearing threshold be defined as the lowest sound pressure level or force level at which responses occur in at least 50% of ascending trials.

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