As discussed in Section 15.5, human perception of loudness follows a logarithmic
scale. The unit used to measure sound intensity level is the decibel (dB).
The simulation is an attempt to familiarize you with the decibel scale and
changes in sound level. Refer to example 15.5 to understand the meaning
of a drop of 3 dB.
The decibel scale is used for a variety of disciplines in science, particularly
in electronics. It is usually used in fixed scales with a suitable known
reference point. For example, as shown in the book, when a "sound intensity
level" in air is given in dB, the reference sound intensity used is
1 x 10-12 W/m2.
However, it is easier to measure sound pressure rather than the intensity.
For this reason, the more common basic descriptor of sound is the "sound
pressure level." The sound pressure level is also expressed in dB,
and in this case the reference sound pressure is 20 micropascals.
Note: the Reference Level in this demonstration applet will give an arbitrary
sound pressure level which is dependent upon your equipment settings.