The decibel Unit Symbol = dB, is a relative unit of measurement corresponding to one tenth of a bel (B).
It is used to express the ratio of one value of a power or field quantity to another, on a logarithmic scale, the logarithmic quantity being called the power level or field level, respectively. Decibels are often used in measuring telecommunication signals. The unit decibel is used because a one-decibel difference in loudness between two sounds is the smallest difference detectable by human hearing.