Environmental Audio Extensions

The Environmental Audio Extensions (or EAX) are a number of digital signal processing presets for audio, present in Creative Technology Sound Blaster sound cards starting with the Sound Blaster Live and the Creative NOMAD/Creative ZEN product lines. Due to the release of Windows Vista which deprecated the DirectSound3D API EAX was based on in 2007, Creative discouraged EAX implementation in favour of its OpenAL-based EFX equivalent – though at that point relatively few games used the API.
Technology.
EAX is a library of extensions to Microsoft's DirectSound3D, itself an extension to DirectSound introduced with DirectX 3 in 1996 with the intention to standardize 3D audio for Microsoft Windows, adding environmental audio presets to DS3D's audio positioning. Ergo, the aim of EAX has nothing to do with 3D audio positioning, this is usually done by a sound library like DirectSound3D or OpenAL. Rather, EAX can be seen as a library of sound effects written and compiled to be executed on a DSP instead of the CPU, often called "hardware-accelerated".
The aim of EAX is to create more ambiance within 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 E-mu 10K1 on Creative Technology's and the Maestro2 on ESS1968 chipset 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 'wavetable' sample-based synthesis cards (which is often confused with the "wavetable synthesis" developed by Wolfgang Palm of PPG and Michael Mcnabb in the late-1970s, however not related). 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.
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 (simulating a wall between player and sound source).
EAX was used in many popular titles of the time, including "Half-Life", "Doom 3", "F.E.A.R.", "Counter-Strike", 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). Creative cards are generally backwards compatible with older EAX versions, although hardware accelerated DSP processing of these effects only happens on cards with EMU chips. Most audio solutions from Creative released after the X-Fi Titanium HD (except for the Audigy Rx) and other companies offer EAX software emulation of varying degrees instead.
EAX 2.0.
EAX 2.0 is supported by Sound Blaster Live! sound cards
EAX 3.0.
EAX 3.0 is supported by E-mu 10K-based products such as the Sound Blaster Audigy
EAX 4.0.
EAX 4.0 is supported by Audigy series sound cards.
EAX 5.0.
EAX 5.0 is supported by E-mu 20K-based products such as the Sound Blaster X-Fi (except the Xtreme Audio cards).
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.
Wine implements software emulation of a subset of EAX.
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 (sample-based synthesis) with DirectSound acceleration, but without hardware accelerated 'wavetable' sample-based synthesis. DAC is rated 95 dB Signal-to-Noise Ratio.
It is available as an integrated option for Dell Inspiron, Studio and XPS notebooks.
Later versions of the driver support EAX 5.0.
Sound Blaster X-Fi MB.
It features:
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.
EAX-like technology is also present in several digital audio players by Creative Technologies, such as the NOMAD and ZEN lines. In these devices, the following effects and features are implemented: