## Decibel (dB)

#### Decibel (dB)

A logarithmic unit of the ratio of a quantity, usually power or intensity levels relative to a specified level. For example, when used to describe the gain or loss in power it is defined as:

$\text{Level in dB}=10\text{\hspace{0.17em}}\mathrm{log}\frac{\text{power level 2}}{\text{power level 1}}$

The level in decibels is positive if power level 2 is greater than power level 1, negative if it is less, and zero if they are equal.

early 1900s: deci- [ten] + bel (the unit being one tenth of a bel, named after Alexander Graham Bell).