Definition of the decibel
The bel is a logarithmic unit used to express the ratio between two values,
and a reference
, of a physical quantity. The decibel is a tenth of a bel. A level
is calculated with the following method:
.
The quantity under study
is, in general, a power. For field quantities
(speed, pressure, force, voltage...) which need to be squared to obtain the power, the level in decibels is given by the following relation:
.
