ISO 28961:2012 provides descriptive statistics, percentiles, of the hearing threshold distribution whose mean is the reference threshold value specified in ISO 226 and ISO 389-7. The mean and percentile thresholds are specified under the following conditions: a) the sound field in the absence of the listener consists of a free progressive plane wave (free field); b) the sound source is directly in front of the listener (frontal incidence); c) the sound signals are pure (sinusoidal) tones; d) the sound pressure level is measured in the absence of the listener at the position where the centre of the listener's head would be; e) listening is binaural; f) the listeners are otologically normal persons within the age range 18 years to 25 years inclusive.
The percentiles are given in numerical form for the preferred frequencies in the one-third-octave series from 20 Hz to 16 000 Hz inclusive, in accordance with ISO 266, and for some intermediate audiometric frequencies.
The percentiles are applicable to the assessment of an individual's hearing in relation to the distribution of hearing thresholds under the above conditions. The percentiles can also be used to evaluate the audibility of low-level noise around hearing threshold.