A unit for describing the ratio of two powers or intensities, or the ratio of a power to a reference power; in the measurement of sound intensity, the pressure of the reference sound is usually taken as 2 × 10^-4 dyne per square centimeter; equal to one-tenth bel; if P₁ and P₂ are two amounts of power, the first is said to be n decibels greater, where n = 10 log₁₀ (P₁/P₂). Abbreviated dB.