![]() Therefore, a change of 10 dB may not necessarily represent a true threshold shift. There is a test-retest variability of ±5 dB. Thresholds are measured clinically in 5-dB steps. This is particularly true at 30 Hz, where “notches” in audiometric configuration often typify noise-induced hearing loss. However, when threshold differences between adjacent octaves exceed 15 dB, inter-octave frequencies should be tested. Most testing is administered at discrete octave frequencies. Instead, the range includes the frequencies considered to be essential for understanding speech (250–8000 Hz). The typical range of frequencies tested does not cover the entire range of human hearing (20–20,000 Hz). Intensity is designated on a normalized decibel hearing level (HL) scale that takes into account the differences in human sensitivity as a function of frequency. Threshold is defined as the softest intensity level that a pure tone (single frequency) can be detected 50% of the time. The audiogram is a graph that depicts threshold as a function of frequency.
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