The unit that measures the intensity (loudness) of sound. It is used to express the degree of a person’s hearing loss. The smaller the number, the better the hearing. Normal hearing thresholds range between 0 and 20 dB. More technically, a decibel is a unit of measure that defines sound intensity (loudness) based on sound pressure level (db SPL). Decibels also measure how a person’s hearing compares with a normal hearing level (db HL). A decibel is one-tenth of a Bell. (Named after Alexander Graham Bell.) It is the loudness units hearing level and hearing loss are measured in. The decibel is a relative measurement of sound intensity or pressure, based on a logarithmic relationship between two sources where one serves as the reference. 0 dB is the baseline norm—not the absence of sound. People with very sensitive hearing can hearing sounds softer than 0 dB. Sounds softer than 0 dB are expressed in negative numbers, thus -20 dB.