4.55  reference equivalent speech recognition threshold level. For a specified speech signal, type of transducer, and method of signal presentation, mean value of the speech recognition threshold levels of a sufficiently large number of otologically normal persons of both sexes between the ages of 18 to 30 years inclusive, expressing the speech recognition threshold in a specified acoustic coupler for a specified type of transducer. Abbreviation, RESRTL; unit, decibel (dB).

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