decibel A unit used to compare two power levels, usually applied to sound or electrical signals. Although the decibel is one tenth of a bel, it is the decibel, not the bel, that is invariably used. Two power levels P and P₀ differ by n decibels when n = 10log₁₀P/P₀. If P is the level of sound intensity to be measured, P₀ is a reference level, usually the intensity of a note of the same frequency at the threshold of audibility.

The logarithmic scale is convenient as human audibility has a range of 1 (just audible) to 10¹² (just causing pain) and one decibel, representing an increase of some 26%, is about the smallest change the ear can detect.

decibel (dB) One-tenth of a bel (named after Alexander Graham-Bell) and the unit in which two power levels are compared. It is used most commonly in acoustics and in describing electrical signals. The decibel difference (N) between the largest (A_max) and smallest (A_min) measurable amplitudes is given by N = 20log₁₀(A_max/A_min). The ratio of values for two power levels, P₁ and P₂, is given by N = 10log₁₀(P₁/P₂).

dec·i·bel / ˈdesəˌbel; -bəl/ (abbr.: dB) • n. a unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale. ∎  (in general use) a degree of loudness: his voice went up several decibels.

decibel (symbol dB) Logarithmic unit, one tenth of a bel, used for comparing two power levels and for expressing the loudness of a sound. The faintest audible sound (2 × 10⁻⁵ pascal) is given an arbitrary value of 0dB. The human pain threshold is c.120dB. Ordinary conversations occur at 50–60 dB.

decibel. Logarithmic unit which expresses difference between different intensities of sound-levels or differently-powered electric signals.