Prisms on a surface splitting light

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:

Level in dB=10log power level 2 power level 1 MathType@MTEF@5@5@+=feaagCart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqipu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeiiaiaabYeacaqGLbGaaeODaiaabwgacaqGSbGaaeiiaiaabMgacaqGUbGaaeiiaiaabsgacaqGcbGaeyypa0JaaGymaiaaicdacaaMc8UaciiBaiaac+gacaGGNbWaaSaaaeaacaqGWbGaae4BaiaabEhacaqGLbGaaeOCaiaabccacaqGSbGaaeyzaiaabAhacaqGLbGaaeiBaiaabccacaqGYaaabaGaaeiCaiaab+gacaqG3bGaaeyzaiaabkhacaqGGaGaaeiBaiaabwgacaqG2bGaaeyzaiaabYgacaqGGaGaaeymaaaaaaa@5D6E@

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).