Game Development Reference
In-Depth Information
Volume and Distance
The farther the sound source, the quieter it is; the closer we get, the
louder it becomes. Middleware allows us to set up simple models that
raise and lower the volume level depending on the player's distance from
an object. The sound designer must assign a certain minimal distance at
which the sound starts fading out. While the signal is within this distance,
it can only change its position; when it crosses a threshold or border, the
volume will then be reduced by a curve of some type, similar to a i lter
slope but af ecting the whole signal.
An example of volume and distance at work. The
listener is actually outside the Max Distance radius—
this means they will hear no sound. Going inward
increases the sound's volume until the Min Distance is
reached. At that point the sound will not get any louder.
The sound will keep on getting quieter until it reaches the maximum
distance, where it's too far to be heard. The farther the maximum
distance, the longer the sound will be heard. In most cases the
volume level is based on a logarithmic curve, because that's more
natural to the way we hear sounds. However, this can be altered
to fit the game's situation depending on the desires of the sound
designer.
Occlusion
Sounds can be muffled by a wall or blocked by other objects.
Occlusion occurs when a sound source is indistinctly perceived from
an enclosed space. A perfect example of this would be if you were
outside of a loud nightclub with the doors closed. As you get closer
you hear more sound but the doors are still blocking the majority of
the higher frequencies.
Occlusion occurs when a source is completely cut of . In
this example, the sound inside the room is heard cleanly
and at full range. Outside of the wall however the sound
is mul ed, often losing its high frequency.
To simulate this environmental impact, audio middleware engines use
i ltering in real time based on a character's distance. When the character
enters the room, the i ltering is removed so that the complete source is
then heard.
Obstruction
When the direct path to a sound is mul ed but not enclosed, this is
an example of obstruction. The sound source and the listener are in
the same room, but an object blocks the direct path to the listener's
ear. For example, open your door and take a listen to your TV or stereo
while still standing outside the room. The sound bounces of the walls
and other objects before it reaches your ear and as a result the sound
is transformed. In a game, the audio engine can be set to account for
varying rel ection times, surfaces and distance using complex algorithms
to accomplish this task.
Obstruction happens when a sound source is not
completely blocked. This results in the sound bouncing
of various surfaces (rather than being directly
perceived), which creates delays and/or rel ections.
