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dB---the
term used to identify ten times the common logarithm of the ratio of two like
quantities proportional to power or energy. (See level, sound transmission
loss.) Thus, one decibel corresponds to a power ratio of 100.1.
Source:
http://www.owenscorning.com/around/sound/glossary.asp
- (abbreviated dB): The decibel is a unit of measure of sound level. The number
of decibels is calculated as ten times the base-10 logarithm of the squared
sound pressure (often frequency weighted), divided by the squared reference
sound pressure of 20 • Pa, the threshold of human
hearing.
Source:
http://www.volpe.dot.gov/acoustics/docs/1990-1999/1999-1.pdf
- The human ear responds logarithmically and it is convenient to deal in logarithmic units
in audio systems. The bel is the logarithm of the ratio of two powers, and the decibel is
one tenth of a bel. Symbol, dB.
a. A dimensionless measure of the ratio of two powers, equal to 10
times the logarithm to the base 10 of the ratio of two powers P1/P2.
b. One-tenth of a bel.
The power P2 may be some reference power; in
electricity, the reference power is sometimes taken as 1 milliwatt (abbr
dbm); in acoustics, the decibel is often taken as 20 times the common
logarithm of the sound pressure ratio, with the reference pressure as
0.0002 dyne per square centimeter.
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