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 Features
Creating an Interactive
Audio Environment
Ambient Sound
Ambient sound refers to the sound world that is generated from a player's
location in the game space. It is a system of indirect and environmental
cues that immerse a player in a particular setting. As in my real-world
example, we are surrounded by ambience all of our lives - a complex web
of sound. However, ambience is the most underdeveloped side of sound design
in interactive media. A game with little or no ambient sound presents
little or no connection to how we perceive the outside world with our
ears. An ambient sound world might be as simple as a single looping track
of forest sounds or a system of sound-producing objects all linked together
by their location within a given game environment.
The environment can communicate to the player information important for
the game-playing experience. For example, a raven flies by in a forest,
making a screeching sound that informs the player that he or she has ventured
too far. A swamp makes a menacing gurgling sound, informing the player
that he or she shouldn't go there. The sound of a portal opening and closing
in the distance informs the player that he or she is close to the level's
exit.
Environmental ambiences fully transport a player into the world presented
by the game. In Claw, each level has a distinct set of ambient
sounds based on the terrain that the main character is encountering. Within
a terrain, a single (environmental) looping sound is used (such as the
sound of a forest), along with a set of sounds (indirect cues) that are
triggered either by Claw's location on the map or by random chance. For
example, the sound of a character whistling in a window matches the animation
of the character shaving and the background ambience of village noise.
When Claw moves through another terrain, the looping ambient sounds would
cross-fade, and another set of ambient trigger sounds would be selected
that corresponds to the new terrain.
In Blood, I used ambience to enhance the atmosphere, as well as
to connote physical environments. In a temple, distant chanting is heard
(though the source of the chant is never discovered) (Figure 4). In a
narrow hallway, whispers surround the player from all sides. The inclusion
of atmospheric elements adds to the spooky and scary nature of the game's
look and feel.
Tips and Techniques
- Try to use consistent reverb settings. All sounds within a given
environment should have a similar set of reverb settings that place
the entire sound world within a consistent acoustic space. There are
foreground and background elements that do stand out from within the
ambience, but not so far as to mistake these sound elements for characters
or objects that a player must encounter.
- Make your loops seamless. The looping ambiences in the game need
to be smooth and unnoticeable. Large variations in pitch or amplitude
will make the loop quite recognizable and annoying after a while. A
rhythmic pattern works well (like the sound of crickets), if it's cut
perfectly. Also, a longer sound sample will help mask the loop point.
- Avoid loops. Though seamless loops are not an impossibility, it's
best to use trigger ambiences whenever possible. Trigger ambiences help
mask the loop point, as well as provide overall variety in the ambience.
In Kesmai's Air Warrior, I used trigger ambiences to convey the
sound world of a World War II airfield. During any given time, an airplane
fly-by sound, a vehicle drive-by sound, and an airplane startup sound
would be selected and played from a set of 50 or so trigger ambiences.
Since these trigger ambiences were selected randomly and played at random
times, the sound world was always changing and seldom repetitive. Another
method of avoiding loops is to queue similar sounds one after another.
A set of three or four sounds that fit seamlessly end-to-end will work
well if they are selected to play on a single channel randomly. This
helps break up the pattern created by a single looping sound.
- Try to create fine gradations of ambiences. Say we're walking from
a forest into a mountain pass. We start out in a deep forest then walk
through a leafy forest then into a meadow before reaching the mountain
pass. If we have a single sound for the forest ambience, no matter how
the forest changes, the ambience will remain the same until we change
scenery drastically when we reach the mountain pass. However, if we
subdivide the forest into three gradations (deep, leafy, meadow), we'd
be better able to convey to the listener the transition of environments
from forest to mountain pass.
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