Units of measurement expressing ratios of power that use logarithmic scales to give results related to human aural or visual perception. Many different attributes are given to a reference point termed 0 dB, for example a standard level of sound or power with subsequent measurements then being relative to that reference. Many performance levels are quoted in dB, for example signal to noise ratio (S/N).
Decibels are given by the expression:
10 log10 P1/P2
where power levels 1 and 2 could be audio, video or any other appropriate values.