Properties of DB Scales
In every kind of
dB, a
factor of 10 in amplitude increase corresponds
to a
20 dB boost (increase by 20 dB):

and

, of course. A function

which is
proportional to

is said to ``fall off'' (or ``roll off'') at the
rate of
dB per decade. That is, for every factor of

in

(every ``decade''), the amplitude drops

dB.
Similarly, a factor of 2 in amplitude gain corresponds
to a 6 dB boost:
and

dB
A function

which is proportional to

is said to fall off
dB per octave. That is, for every factor of

in

(every ``octave''), the amplitude drops close to

dB. Thus, 6 dB
per octave is the same thing as 20 dB per decade.
A
doubling of power corresponds to a
3 dB boost:
and

dB
Finally, note that the choice of
reference merely determines a
vertical offset in the
dB scale:
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Negative and Imaginary Numbers