Sound - Game Programming Algorithms and Techniques - page 147

once the player crosses over into a marked region, we want to slowly interpolate
between the reverb being off and on, to make sure that the transition feels organic.
Note that there is one big caveat to using convex polygons to mark DSP regions. If
it's possible to have areas above or below other areas in the level, and those areas
have different DSP effect needs, this approach will not work. So, for example, if
there is a tunnel that goes under a grassy field, a convex polygon for the tunnel
would also flag the areas above the tunnel as needing the DSP effect. If this prob-
lem must be solved, instead of a convex polygon you will have to use a bounding
volume of some kind, which is also covered in Chapter 7 .
Other Sound Topics
Although this chapter has covered a great deal of topics related to sound, there still
are a couple items that didn't really warrant entire sections but at least should be
mentioned in some capacity.
Doppler Effect
If you stand on a street corner and a police car drives toward you with its sirens
on, the pitch of the sound increases as the police car approaches. Conversely, once
the police car passes by, the pitch of the sound decreases. This is a manifestation
of the Doppler effect , which is demonstrated in Figure 6.6 .
Figure 6.6 Doppler effect on a police car siren.
The Doppler effect (or Doppler shift ) occurs because sound waves take time to
travel through the air. As the police car gets closer and closer to you, it means each