What is the difference between dBv, dBu, dBV, dBm, dB SPL, and plain old dB? Why not just use regular voltage and power measurements?
Our ears respond logarithmically to increases in sound pressure level. In order to simplify the calculations of these levels, as well as the electrical equivalents of them in audio systems, the industry uses a logarithmic system to denote the values. Specifically, the decibel is used to denote logarithmic level above a given reference. For instance, when measuring sound pressure level, the basic reference against which we take measurements is the threshold of hearing for the average individual, 10^-12 W/m^2. The formula for dB SPL then becomes: 10 Log X / 10^-12 where X is the intensity in watts per square meter The first people who were concerned about transmitting audio over wires were, of course, the telephone company. Thanks to Ma Bell we have a bunch of other decibel measurements. We can use the decibel to measure electrical power as well. In this case, the formula is referenced to 1 milliwatt in the denominator, and the unit is dBm.
