Normal hearing is defined as thresholds below 30 dB across 125-4000 Hz

Evidence

Listeners with audiometric thresholds of < 30 dB HL at all the frequencies between 125 and 4000 Hz in both ears were classified as normal-hearing; otherwise, as (mildly) hearing-impaired. — Dijk, Pim van, Physiology, Psychoacoustics and…, 1031

Categorization

• DEFINE: Operational definition of normal hearing used in the study - a useful methodological anchor.