A decibel (dB) is a unit used to express relative differences in signal strength. A decibel is expressed as the base 10 logarithm of the ratio of the power of two signals, as shown here:
dB = 10 x Log10 (P1/P2)
where Log10 is the base 10 logarithm, and P1 and P2 are the powers to be compared.
Note: Log10 is different from the Neparian Logarithm (Ln or LN) base e logarithm.
You can also express signal amplitude in dB. Power is proportional to the square of the amplitude of a signal. Therefore, dB is expressed as: