Environmental Audio Extensions
The environmental audio extensions (or EAX) are a number of digital signal processing presets for audio, present in Creative Technology's later Sound Blaster sound cards and the Creative NOMAD/Creative ZEN product lines. EAX displaced the alternative A3D (Aureal 3-Dimensional) in 2001. As of 2010, EAX is rarely used, with modern games utilizing the CPU to process 3D audio rather than relying on dedicated hardware.
The aim of EAX is to create more ambience within computer and video games by more accurately simulating a real-world audio environment. Up to EAX 2.0, the technology was based around the effects engine aboard the EMU10K1 on Creative Technology's and the Maestro2 on ESS1968 chipsets driven Sound Cards. The hardware accelerated effects engine is an E-mu FX8010 DSP integrated into the Creative Technology's audio chip and was historically used to enhance MIDI output by adding effects (such as reverb and chorus) to the sampled instruments on sample-based synthesis cards (also known as wavetable synthesis). A similar effects DSP was also present on Creative's cards back to the AWE 32. However, the EMU10K1's DSP was faster and more flexible and was able to produce not only MIDI output but also other outputs, including the digital sound section. A person who has been exposed to MIDI effects processors will quickly recognize the parameters that EAX controls, and the names of many of the presets.
Creative Technology, seeing the rising popularity and marketing significance of having a proprietary sound API, gave the functionality of this effects engine the name EAX. EAX is a library of extensions to Microsoft's DS3D API, adding environmental audio presets to DS3D's audio positioning. Developers taking advantage of EAX choose an environment for their game's setting and the sound card uses the mathematical DSP digital filter presets for that environment. The original EAX was quite primitive, only offering 26 presets and 3 parameters for more accurate adjustment of the listener parameters and 1 parameter for the sources. Each revision of the technology increased the available effects. EAX Advanced HD (also known as EAX 3) and up provide support for new environmental transitions, new effects, and multiple active effects. Further additions include smooth changes between EAX environment presets and audio occlusion effects (that is, a wall between player and sound source).
The aim of EAX has nothing to do with 3D audio positioning. This is usually done by a sound library like Microsoft's DirectSound3D or OpenAL. Rather, EAX can be seen as a library of hardware-accelerated sound effects. EAX is used in many popular titles including Doom 3 and Prey. These games support EAX 4.0 if audio hardware with an OpenAL-supporting driver is present. Because hardware acceleration for DirectSound and DirectSound3D was dropped in Windows Vista, OpenAL will likely become more important for game developers who wish to use EAX in their games.
Most releases of EAX versions coincide with increases in the number of simultaneous voices processable in hardware by the audio processor: the original EAX 1.0 supports 8 voices, while EAX 5.0 allows 128 voices (and up to 4 effects applied to each).
Versions of EAX 
EAX has had many iterations, each with an increasing number of features. Below is an overview of the currently available versions of EAX and their added features in respect to the previous version.
EAX 1.0 
- 8 simultaneous voices processable in hardware
- 32 individual 3D voices
- Environmental Effect Presets
- Per-channel individual environmental presets
- Hardware DSP Rendering.
EAX 2.0 
- 32 simultaneous voices processable in hardware
- Occlusion Effects
- Material-specific reverb parameters
EAX 3.0 
- 64 simultaneous voices processable in hardware
- 'Smoothing' between 3D audio environments
- Direct access to all reverb parameters
- Environmental Panning
- New reverb engine
- Beginning of the AdvancedHD Designation from new reverb engine
EAX 4.0 
- Real-time hardware effects
- Multiple simultaneous environments
- Ring modulation effects
EAX 5.0 
- 128 simultaneous voices processable in hardware and up to 4 effects on each
- EAX Voice (processing of microphone input signal)
- EAX PurePath (EAX Sound effects can originate from one speaker only)
- Environment FlexiFX (four available effects slots per channel)
- EAX MacroFX (realistic positional effects at close range)
- Environment Occlusion (sound from adjacent environments can pass through walls)
Future development 
According to Creative's OpenAL 1.1 specification, EAX should be considered deprecated as a developer interface. New development should use OpenAL's EFX interface, which covers all the EAX functionality and is more tightly coupled with the overall OpenAL framework.
EAX emulation 
In addition to hardware devices, Creative also released EAX emulation drivers for computers with only onboard audio.
The differences lie in the software bundle. Sound Blaster Audigy ADVANCED MB includes Creative Audio Center, Creative MediaSource 5 Player/Organizer, Creative WaveStudio 7, Creative ALchemy; Sound Blaster X-Fi MB includes Entertainment Console, Creative Karaoke Player, Creative MediaSource 5 Player/Organizer, Creative WaveStudio 7, Creative Audio Console, Creative ALchemy.
Sound Blaster Audigy ADVANCED MB 
Also known as Sound Blaster Audigy ADVANCED MB, it is similar to Audigy 2 SE, but the software supports EAX 3.0, which supports 64-channel software wavetable with DirectSound acceleration, but without hardware accelerated wavetable synthesis. DAC is rated 95dB Signal-to-Noise Ratio.
Later versions of the driver supports EAX 4.0.
Sound Blaster X-Fi MB 
- EAX 4.0 and OpenAL support
- Graphic Equalizer
- Creative ALchemy (Windows Vista only, is used for providing EAX in Vista)
- Console Launcher (Entertainment Mode)
- Audio Console
- Karaoke Player
- Creative WaveStudio
- Creative MediaSource
Unlike its predecessor, Audigy Advanced MB, X-Fi MB does not include a software-based SoundFont synthesizer. Another difference is that it has the option to run in 30-day trial mode.
Audio player versions 
- Different reverb-like environments
- Speed-shifting (slower or faster)
- Environment adaptation (train, plane, public place etc.)
- Sound image (broad, narrow etc.)
- A simple graphical equalizer
See also 
- A3D (Aureal 3-Dimensional, now defunct)
- Dolby Surround / Dolby Pro Logic / Dolby Digital
- List of video games that support EAX
- Do you really need discrete audio? - The Tech Report, 21 November 2010
- An Audiophile’s Guide to Battlefield Bad Company 2 - EA, 22 Jan 2010
- "OpenAL and Windows Vista"., Creative Labs
- 'OpenAL, EAX and EFX' section explains 'EAX' vs 'EFX'