In acoustics, the decibel (dB) scale is a scale for
measuring the relative loudness of
two sounds. For example, environmental noise is often measured as follows:
Where L is the sound pressure
level (in dB), p is the sound pressure amplitude, and p0 is a reference amplitude of 20 micropascals (less
than one billionth of atmospheric pressure). On this scale, a barely
audible sound (p = p0) has a sound pressure level of 0 dB, normal conversation (p = 1,000*p0) is at a level of around 60 dB,
and a jet engine at close range (p = 1,000,000*p0) is at a level of around
120 dB.
Similar decibel scales are used in other branches of science and engineering to measure electrical
power levels and other signal levels, always
with respect to some reference level.
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