Decibel

The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power or intensity) relative to a specified or implied reference level. Since it expresses a ratio of two (same unit) quantities, it is a dimensionless unit. A decibel is one tenth of a bel (B).We perceive loudness of sound as the logarithm of the actual sound intensity, and dB (decibels) are a logarithmic scale.