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 in 2007, which deprecated the DirectSound3D API that EAX was based on, 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 was 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.