The Decibel (dB)
Definition: The standard unit for measuring sound. A subjective scale where one unit equals one increment of “loudness.”
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There decibel is used frequently within audio applications. The decibel is used to express the relative levels of two electrical voltages. It is essentially a ratio which we can use to work out how "loud" something appears to be. As the scale is logarithmic, twice the dB value does not mean twice the loudness. There are also several variations on the dB unit which are important to remember as they mean different things.
dBm - This is a variation on dB, referenced to 0dB = 1mw (600ohms). This unit is usually used within electronics and fibre-optics but it can appear on certain devices.
dB/Octave - This is used for measuring the slope of a filter. The more dB's per octave, the sharper the filter slope.
dBv(dBu) - This is another variation on dB which can be seen as either dBv or dBu. It is perhaps more common to see dBu used as dBV can be easily mistaken for it. The "u" stands for unloaded. This unit is referenced at 0.775 volts.
dBV - As before, this is a variation on dB but the reference level is 1 volt (no impedence).