The decibel scale is a logarithmic scale that measures the intensity of sound. It is defined as
where is the base-10 logarithm and is the threshold of hearing,
The intensity is then described as being decibels, abbreviated dB.
References
Bekefi, G. and Barrett, A. H. Electromagnetic Vibrations, Waves, and Radiation. Cambridge, MA: MIT Press, pp. 134-137, 1987.
