Game Development Reference
In-Depth Information
Table 26-1. Typical sound intensities
Typical intensity
Jet airplane, fairly close
150 dB
Gun shot
160 to 180 dB depending on the gun
Crying baby
130 dB (painful!)
Loud scream
Up to 128 dB (world record set in 1988)
Typical conversation
50 to 60 dB
About 10 dB
The intensity values shown in Table 26-1 are typical and surely there's wide variation in
those levels depending on, for example, the type of aircraft, or the person you're talking
to, or the softness of the person's voice whispering to you. It's common sense, but if
you're writing a game you'll want to reflect some level of realism in the intensity of
various sound effects in your game.
Now, intensity is actually a logarithmic scale. It is generally accepted that a sound meas‐
ured 10 dB higher than another is considered twice as loud. This is perceived loudness.
Thus, a crying baby is way more than twice as loud as a normal conversation. Parents
already know that.
Characteristics of and Behavior of Sound Waves
Now that we've established what sound is, we're going to generally refer to sound
waves throughout the remainder of this chapter. Remember, sound waves are pressure
waves that get interpreted by our brains as sound. The bottom line is that we're dealing
with waves, longitudinal waves. Therefore, we can use principles of wave mechanics to
describe sound waves. Furthermore, since sound waves (think pressure waves) displace
real mass, they can interact with the environment. We already know that pressure waves
interact with our eardrums to trigger some biochemical action, causing our brains to
interpret sound. Conversely, the environment can interact with the pressure wave to
alter its characteristics.
Harmonic Wave
Let's consider a one-dimensional harmonic pressure wave—one that could be created
by the driven piston shown in Figure 26-1 (a). Let the x-direction correspond to distance,
positive from left to right. Thus, the wave of Figure 26-1 (a) travels in the positive x-
direction. Let Δ P represent the change in pressure from the ambient pressure at any
given time. Let A P represent the amplitude of the pressure wave. Remember, the pressure
will vary by some amount greater than the ambient pressure when condensation occurs
to some amount lower than ambient pressure when rarefaction occurs. The range in
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