The Decibel

The decibel (dB) is the unit of relative power. If one signal is twice as loud as another, it has a gain of 3dB. One advantage of expressing power in decibels is that, in a multi-stage amplifier, the power gains of the stages can simply be added together.

 

 Output Power (in mW)   The system has dB gain
  
Input Power (in mW)