Pure tone and speech audiograms are measured in dB HL (hearing level). In normal hearing adult person hearing threshold is 0 dB HL.dB SL (sensation level) is the intensity of sound that will produce same sensation of hearing as in a normal person. Thus in a hearing-impaired individual who already has a hearing loss of 20 dB, a sound of 50 dB will produce a sensation of 30 dB only.dB SPL (sound pressure level) is the physical measure of sound intensity.Environmental sounds (noise pollution levels) are measured in dB A. dB nHL is used in auditory brain-stem response to click stimulus.