Game Development Reference
In-Depth Information
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In this chapter, I
ll explore
both sound effects and music. With a little work and imagination, you should be
able to take what you learn here and create your own sound magic.
ll take you as far as I can into the world of sound. We
Imagine someone on your street working with a hammer. Every time the hammer
strikes a nail, or perhaps the poor schmuck
'
s finger, a significant amount of energy
is released, causing heat, deformation of the hammer, deformation of whatever was
hit, and vibrations in all the objects concerned as they return to an equilibrium
state. A more complete description of the situation would also include high-
amplitude vibration of Mr. Schmuck
'
s vocal cords. Either way, those vibrations are
propagated through the air as sound waves.
When these sound waves strike an object, sometimes they make the object vibrate at
the same frequency. This only happens if the object is resonant with the frequency of
the sound waves. Try this: Go find two guitars and make sure they are properly
tuned. Then hold them close together and pluck the biggest, fattest string of one of
them. You should notice that the corresponding string on the second guitar will
vibrate, too, and you never touched it directly.
The experiment with the guitars is similar to how the mechanical parts of your ear
work. Your ears have tiny hairs, each having a slightly different length and resonant
frequency. When sound waves get to them and make different sets of them vibrate,
they trigger chemical messages in your brain, and your conscious mind interprets the
signals as different sounds. Some of them sound like a hammer striking a nail, and
others sound more like words you
d rather not say in front of little kids.
The tone of a sound depends on the sound frequency, or how fast the vibrations hit
your ear. Vibrations are measured in cycles per second, or Hertz (abbreviated Hz).
The lowest tone a normal human ear can hear is 20Hz, which is so low you almost
feel it more than you hear it! As the frequency rises, the tone of the sounds gets
higher until you can
'
t hear it anymore. The highest frequency most people can hear
is about 20,000Hz, or 20 kiloHertz (KHz).
The intensity of a sound is related to the number of air molecules pushed around by
the original vibration. You can look at this as the
'
applied to anything by a
sound wave. A common measurement of sound intensity is the decibel, or dB. This
measurement is on a logarithmic scale, which means that a small increase in the dB
level can be a dramatic increase in the intensity of the sound. Table 13.1 shows the
dB levels for various common sounds.
“
pressure
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