EAX is just an API developed and controlled by Creative but all other soundcard companies can support the API if they wish for free. Games
using EAX have the Environmental Audio logo on the boxes. It allows you to specify
the components that make up the audio elements that in turn make up an environment.
Environmental Audio is Creative's latest audio technology. It promises to deliver sounds that are
life-like, It is the PC industry's first system that recreates and delivers real-world, interactive audio experiences in games, music, and other audio applications. Environmental Audio is a revolutionary audio platform that takes your PC beyond home-theater
quality. Environmental Audio goes beyond today’s surround-sound and 3D positional audio to actually model an environment with powerful effects that take into account room size, acoustic properties, reverb, echo and many other effects that create a real-world experience.
Reverb
The sound your hear can be split up in a direct path sound and reflected sound. Direct path is the actual sound produced by the sound
source (the original sound) as it travels directly to your ear and the reflections are called reverb, that is the sound waves that have
bounced (i.e. reflected) around on the walls or other objects before they came to you ear. What you will hear is the combination of
original sound and the reverb. The ratio original reverb/sound source are called the wet/dry ratio.
The shape, size and materials of the room/environment and the distance to the sound source will determine the reverb. That's the
reason Creative calls it Environmental Audio.
The only place you will hear only the original sound are in an anechoic chamber. Almost all music and game sound effects you hear have
some reverb applied to them that sounds more compelling than the reverb effect your room will produce.
What sound you hear will also be affected of objects (walls, pillars, other people etc) that the sound waves needs to pass before it
arrives at you ear, that's called occlusion and is supported in A3D2 and will later be added to EAX 2.
To create the reverb effects you can either use the geometry of the room and do the calculations how the soundwaves bounce around
the rooms or do a reverb engine where you simulate different kind of environments without having do actually process the geometry
information. Current hardware can't process all the reflections but Aureal choose to actually calculate the first order reflections (up to 60
reflected sound waves at any time) while Creative instead made the choice do a reverb engine and let the developer choose what kind of
environment the users are located in. Creative made that choice because they think it's easier for the developer to implement, offers
more flexibility for the level designers and requires less processing power.
EAX, which is an extension to DS3D, is an API the developers use to select what reverb effects should be applied
to the sound sources. The developer can change the reverb effect at anytime and the reverb effect will stay the same until the developers
change it again.
The developer will only change the reverb effect depending on what environment the listener are located in not where the sound source
are, except changing the wet/dry ratio depending on how far away the sound sources are. The further away the sound source are the
higher the wet/dry ratio will be, that is most of the sound will consist of reflections if the sound source are far away. The wet/dry ratio will
be calculated automatically by EAX unless the developer wants to change it.
Creative made the choice do a reverb engine and let the developer choose what kind of
environment the users are located in. Creative made that choice because they think it's easier for the developer to implement, offers
more flexibility for the level designers and requires less processing power.
