DirectSound3D API
DirectSound3D is part of the DirectX API. It is a more basic form of 3D positional audio, and requires no prioperity hardware to impliment. Almost all newer sound cards support DirectSound3D in hardware, but for those that don't, the exact same sounds can be processed by the CPU. This isn't a good idea in ost cases because DirectSound3D is more complicated than anyone really thinks, and can become a burden to even the fastest CPUs.
DirectSound3D is an improvement over DirectSound, in that it is capable of more than stero sounds. DirectSound3D is capable of almost an infinite number of speakers, depending on how it is impliemented in the sound card hardware. What DirectSound 3D does is receive information about sounds, such as their content, their 3 dimensional coordinates in X,Y, and Z space, the sound reciever X,Y, and Z coordinates and the sound emmition properties. The sound properties include whether the sound was emmited spherically or conically, whether the sound source was in motion, the orientational direction comparied to the reciever, and atmosphere conductivity.
There are currently 3 different DirectSound3D sound renderers. The first is a software only based solution, which is the fastest to process but least accurate. There are 2 other algorithms, which were designed to run only in hardware but are also capable of being processed by the CPU, if the game developer finds it nessisary. They both have different impimetations of HRTF, head related transfer functions, and the choice is up to whichever the program finds is best suited for the task.
Environmental Audio Extensions (EAX)
EAX is only found enabled through hardware in Creative Labs cards, but can be done through other sound card drivers which emulate the correct functions. There is not software only based solution because the sound rendering tasks are far to complicated to prevent a serious performance hit. What this API is designed to do is to add preset reverberation, that is a blend of different echos, to simulate different enviroments. This makes a clear distinction in sounds whether they are in a small room, large theatre, cave, outside, and so on.
A3D
This is a hardware only based solution made by Aureal that is based on highly acurate and mathematical sound reflections. Unlike all other sound API's, this actually models a 3 dimetional sound stage and allows the ability for sound reflections, instead of just pre-programmed generic echos. This was originally designed by NASA, for use in their simulations, but has found a good home in 3D gaming. A3D 2.0 is capable of 16 3D generica sound streams, plus another 60 sound reflections. For games that do not use the sound reflections, the 60 extra sound channels can be combined with the original 16 for up to 76 discrete sounds.
Other Sound Algorithms
Sensura Algorithms are original reverberation algorithms that pay more attention to multi speaker set-ups, with emphasis on sound timing instead of on the strength of the sounds out of each speaker. It is also hardware compatible with EAX, although the quality of the implimentation isn't as good as a true Creative Labs card.
QSound Algorithms (QSound) is another renderer that is designed to make more out of less. It can make mono sounds sound as if they were stereo, and can virtualize multi speaker setups out of only 2 speakers. This is the sound format used in Sega Dreamcast systems, where the average television is equiped with only 1 or two speakers.
