Game Development Reference
In-Depth Information
implementation of these effects is well beyond the scope of this topic. However,
if you are interested in learning how to implement the effects covered in this sec-
tion, check the references at the end of the chapter. In any event, even though we
won't implement any of the effects, it is worthwhile to at least discuss what the
most common effects represent.
Common DSP Effects
One of the most common DSP effects encountered in games is the aforementioned
reverb. Any game that wants to re-create the echo of loud sounds in enclosed
spaces will want to have some sort of implementation of reverb. A very popular
open source reverb library is Freeverb3, which is available at
ht-
tp://freeverb3.sourceforge.net
. Freeverb3 is an
impulse-driven system
, which
means in order for it to apply the reverb effect to an arbitrary sound, it needs a
source sound file that represents a specific test sound playing in the desired envir-
onment.
Another DSP effect that gets a large amount of use is the
pitch shift
, especially
if Doppler shift (covered later in the chapter) is desired. A pitch shift increases or
decreases the pitch of a sound by altering the frequency. Although a Doppler shift
would be the most common use, another example might be in a car racing game,
where the pitch of the engine might adjust depending on the number of RPMs.
Most of the other DSP effects that see use in games usually modify the range
of frequencies or decibel levels output. For example, a
compressor
narrows the
volume range so that very quiet sounds have their volume amplified while very
loud sounds have their volume reduced. This might be used to try to normalize
volume levels if there are wildly different levels in different sound files.
Another example is a
low-pass filter
, which reduces the volume of sounds with
frequencies (and therefore pitches) higher than the cutoff point. This is commonly
used in games that implement a “shell shock” effect when an explosion occurs
near the player. To sell the effect, time is dilated, a low-pass filter is applied, and a
distinct ringing sound is played.
There are quite a few other effects that might find use in a game, but these four are
some of the most common effects you'll come across.
