Decibel
= Decibel
{title2=$\mathrm{dB}$}
{wiki}
A comparison using a <logarithm> of two <powers> is expressed as $10\log_{10}(P_2/P_1)\,\mathrm{dB}$. Positive loss instead uses $10\log_{10}(P_{\rm in}/P_{\rm out})\,\mathrm{dB}$. For <wave amplitudes>, a factor twenty is appropriate only when the corresponding <power> ratio equals the square of the amplitude ratio.