The decibel (dB) is a unit used to measure sound intensity and other physical quantities. A decibel is one tenth of a bel (B), a unit named after Graham Bell, the inventor of the telephone. Its logarithmic scale is convenient to represent the entire range of human hearing. The decibel of sound pressure level (dB SPL) takes as a reference the minimum sound pressure level that the average human ear can detect. The smallest audible sound to humans is typically 0 dB SPL (hearing threshold). In practice, "dB" often stands for “dB SPL�. Because the decibel scale is logarithmic, a three-decibel increase in sound level already represents a doubling of [sound] intensity. For example, a normal conversation may be about 65 dB and someone shouting can typically be around 80dB. The difference is only 15 dB but the shouting is 30 times as intensive. Please note that perception of loudness is not exactly the same as sound pressure level. To account for the fact that are particularly low and high-pitched sounds appear less loud to the human ear, noise is usually measured in A-weighted decibels (dB(A)).