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Hearing level is the sound pressure level produced by an audiometer at a specific frequency. It is measured in decibels with reference to audiometric zero. Hearing of speech is considered to be impaired when the hearing level is shifted 25 dB or more.
References
"The Audiogram" (PDF). VanAsh Deaf Education Center. Archived from the original (PDF) on 27 February 2012. Retrieved 16 December 2012.
Truax, Barry. "Hearing level". Handbook for acoustic ecology. SFA. Archived from the original on 28 November 2012. Retrieved 16 December 2012.