Environmental effects

Creative's own Environmental Audio Extensions, or EAX for short, is a reverb engine, capable of manipulating sounds in real-time to conform to set EAX environments, which the developer can either choose from a library or tweak themselves. Creative provides a number of options for customizing reverberated sounds, such as Early Reflection Level, Late Reverb Level, Diffusion, Density, Detuning Rate and Depth, High Frequency Cutoff, and so forth, basically mimicking most of the real-time-calculated functions in A3D 2.0 that make it so cool. A developer basically applies EAX effects to areas, walls, specific sounds, etc. It's easy to implement, and it works well across applications.

Aureal decided to take the hard approach, under the premise that we all live in a dynamic world and preset sound filters couldn't effectively convey realism. Basically, what A3D 2.0 does is look at your position in the level, determine what kind of material the walls are, and renders in real-time the first reflection path of any sound you're capable of hearing. The major benefit of this is that supposedly, as you move around the level the sounds around you change drastically; reflections careen off of different walls at different angles and distances as you move, and the human ear can either consciously or subconsciously pick up on these changes.

Toni Schneider mentioned that late-order reflections (after a sound has bounced off more than one wall) tend to fall more into the mish-mash of general (static) reverb, and that is how Vortex 2 will handle them in the next release of A3D. Currently late-order reflections aren't handled at all. In Aureal's test applet, you can dynamically move the sound source, walls, and the listener in real-time, and visually see (as well as hear) the effects of sound reflection and occlusion. To be honest, I couldn't tell worth $##% if there was a wall right next to me or 20 feet away as I moved, but the volume and quality of sound did change noticeably. Was it like, "damn, there's a wall right next to me?" Hell no. To be fair, it's not exactly easy to tell wall placement or dynamic reflection in a real-life room either, but to me, that just begs one important question: is it that important? Well, if you've got the MIPS to spare, why not?

Vortex 2 (and Vortex 1) also calculate occlusions, or sound passing through walls. If you've ever heard someone playing the radio from the next room, hearing only the low bass pounding through the wall, you're hearing sound occlusion. According to Toni, reflections are great, but occlusions are the "big thing," and the most important. I agreed that the occlusion effects were definitely more pronounced, but direct-path occlusions without reflections are, in my opinion, utterly useless (interesting that Toni didn't mention this, as Creative's recently-announced EAX 2.0 includes occlusions and obstructions, but not reflection) without reflection. To illustrate, I set up a demo where three partitions in an open room blocked the direct path of sound to the user (the sound was continually occluded, and by the 3rd barrier, it was completely muted). I then turned off the reflections, and the sound went dead, simply because there were some barriers in the way, even with the rest of the room completely open. By this rationale, if there's a solid metal pole between you and your target, any sound it makes would be completely muted by the occlusion. In this regard, if you calculate real-time occlusions, you MUST compensate with either simulated (static reverb) or rendered reflections, and at this time, it seems the only benefit to having rendered reflections is to cancel out the unnatural artifacts caused by occlusions.

Occlusions with and without reflections

At this time, the only game which 1) supports both EAX and A3D 2.0 and 2) takes place in an environment suitable for such effects, is Half Life, from Valve Software. We've plugged this game enough in our various Half Life articles, but in terms of hardware support, the game takes place in steel tubes, concrete bunkers, enclosed laboratory rooms, and huge resonating chambers - in short, perfect for the effects demonstrated in both A3D 2.0 and EAX. Time to crank up the volume and test some APIs.