Threshold is the level at which a stimulus or a change in stimulus is just sufficient to produce a sensation or an effect.

Hearing threshold sensitivity is usually measured for a series of sinusoids or pure tones. The purpose of this type of test is to determine the softest intensity of a series of sinusoids, which the listener can just barely hear.

For clinical purposes the thresholds are usually measured at octave frequencies between 125 Hz and 8000 Hz. If a difference in threshold is found to exist, which exceeds 30 dB between octave frequencies, then the mid-octave thresholds should be determined as well.

Hearing thresholds are measured in dB HL. Thresholds below 20 dB HL are considered to be within the normal range.