For now, we deal only with 'voltage' amplification (gain) and damping (loss). V2 >V 1 = amplification, dB value is positive and V 2< V 1 = damping, dB value is negative. V2 / V1 means the ratio. The amplification or the damping in dB is: L = 20 × log (voltage ratio V 2 / V 1) V 1 is the reference.
Using voltage we get: Level in dB: L = 20 × log (voltage ratio)
+6 dB = two fold the voltage +12 dB = four fold the voltage +20 dB = ten fold the voltage +40 dB = hundred fold the voltage
Using power we get: Level in dB: L = 10 × log (power ratio)
+3 dB = two fold the power +6 dB = four fold the power +10 dB = ten fold the power +20 dB = hundred fold the power
Bron: Sengpielaudio.com
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