The decibel unit, abbreviated as dB, is used to measure the level of sound. It is widely used in electronics, signals and communication devices, and the scale refers to how high decibel units can go in accordance to power settings. The dB can be described as a logarithmic way of understanding ratio. That ratio may be between sound pressure, power and many other things.
The term first originated from different methods used to quantify the amount of signal lost in telegraph and telephone circuits. The original unit for this loss was MSC, an abbreviation for Miles of Standard Cable. One MSC typically corresponded to a loss of power measured over one mile, or approximately 1.6 kilometers, and it referred to a standard telephone cable length at a frequency of 795.8 Hz or 5,000 radians per every second. The quality was also matched closely with the smallest attenuation detected by the average listener.
In 1924, when Bell Telephone Laboratories first issued the new unit definition, the group received favorable responses. The MSC unit was replaced by the Transmission Unit, abbreviated as TU. One TU represented 10 times the base-10 logarithm of the ratio between measured power and reference power level. It was conveniently chosen for easy substitution with MSC measurements.