A unit of level equal to ten times the logarithm of the ratio of two powers. Depending on the reference level used, the decibel symbol will be immediately followed by a letter, as: dBA – An “A” weighted decibel level. dBB – A “B” weighted decibel level. DBC – A “C” weighted decibel level. dBm – A decibel level in which Pb represents one milliwatt of power dissipated in a 600 ohm line. Pa must a also be measured in a 600 ohm line. DBV A decibel voltage level, in which the reference, Vb, is 1.0 volt. A reference of 0.775 volts is also frequently used.