![]() Whenever power, voltage, etc., is converted to a dimensionless ratio (the first step in translation to decibel), the denominator in the division operation will often be a standard reference value such as one milliWatt or one milliVolt. This effect is prominent, however the underlying rationale is not obvious and has to do with the mathematical properties of logarithms. ![]() Logarithmic scaling pushes large values closer together and spreads small values further apart. (Physicists regard all units of measure as “dimensions”, hence a value that is not accompanied by physical units of measure is “dimensionless”.)įact #2: Decibel scaling is logarithmic. When the given quantity is divided by the reference value, the physical units of measure vanish. Relative density is obtained by dividing the density of a given substance by the density of another substance used as a reference, usually water. ![]() Mach numbers are obtained by dividing a given speed by the speed of sound, which is used as a reference. Two familiar examples of dimensionless ratios are Mach numbers and relative density. Let’s begin with two essential facts about decibels:įact #1: Decibel values are a type of “dimensionless ratio”. Each of these different physical quantities is either a form of power or else has a very specific and simple relationship with power. ![]() Decibels are used routinely for expressing electrical power, electrical voltage, sound power and (more commonly) sound pressure level (SPL). ![]()
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