Aureal A3D vs DirectSound 3D
(Based on DirectX 5)

There are 3 major differences between A3D and DS3D, maybe 4.

First and foremost you will notice a much greater positional effect using A3D.  A3D uses Head Related Transfer Functions (HRTFs) to produce binaural signals to recreate exactly what each ear will hear when a sound source comes from a particular direction and is moving along a particular vector at a particular speed.  This allows for much greater precision and quality than DS3D, which uses simple Inter-Aural Time Differences (ITD) and Inter-Aural Intensity Differences (IID). ITD and IID do not allow for above and below the listener properly, and thus there is essentially no up-down in DS3D.    Front-back in A3D is much more pronounced as well.  Other psycho-acoustic effects are taken into account using A3D including such things as environmental or atmospheric rolloff (or absorption); non-existent in DS3D.

Second is speed.  Positional audio is a computationally-intensive process.    Millions of calculations can take place in less than a second and doing them on the host CPU will cost almost any application loss in frame-rate and overall speed.   As you know speed is king, and developers are very reluctant to use DS3D for this very reason.

Reasons 3 and 4 can be rolled into 1 depending upon how you look at them, but for clarity's sake I will set them apart.

Reason 3 is the extra, or extended, features of A3D.  Under generic DS3D Microsoft does not take into account for hardware limitations, thus generic DS3D accelerators will very rapidly run out of free 3D hardware channels (generally after the first 5 - 8 sounds are created).  Once there is no more free hardware all other sounds are rendered in software 3D or dropped back to 2D. Yikes!  This means that first of all you will suffer from speed issues for all but the first sources, and that each software 3D source will sound different than the hardware sources (and who's to say that you will actually ever get to hear those hardware 3D sources?  Hundreds of sounds are created and many are never played.)  If you wish to drop the sources back into 2D, you can imagine the confusion this will create and how it really defeats the purpose. Aureal has created an extended feature call in their API to enable automatic resource management.  What this does is automatically shuffle sources on and off the hardware as needed, and in the most intelligent way (as deemed by the priorities of the developer). This means that a developer can throw a very simple flag in our API and have us do all the work of optimizing the use of the available 3D sources.  No sounds have to be dropped to 2D and no sounds have to be rendered in software, so what you get is basically unlimited, beautifully rendered A3D sources, regardless of the limitations of the particular sound card.

The 4th reason is the environmental effects (as these are extended features of A3D, you can roll them into reason 3).  Developers currently have access to additional A3D features that DS3D and other 3D audio solutions do not: high-frequency rolloff for underwater and fog effects, automatic obscuration, for when sound sources, or the listener move behind a sound-reflective object (like a wall or a closed door), as well as automatic reflections off of walls, floors, and ceilings.  The first is great for rapidly and easily affecting all or individual sounds to reflect the sound's or the listener's immersion in an absorbing matter such as water, clouds, fog, etc.  The second is very useful to developers who don't want to track every wall, truck, building, or big monster that might get in the way of a sound wave's direct path to the listener; A3D attenuates the sound and simulates the transmission losses automatically.  The third is great for properly (and automatically) recreating the proper size of a room (in aural terms) to the listener.   In larger rooms reflections should take longer to bounce off walls and return to the ear. Reverb is generally a very bad positional technique that actually muddies the spatial field.  Reflections are much more effective.   Reflections are also very useful for guiding oneself in the dark....with A3D you can begin to imagine audio-only games!

By Skip McIIvaine at Aureal Inc

Site
About
News
News Archive

Audio
3D Sound Software
Interviews
Sound Cards

Files
Drivers
Game Demos
Game Updates
Utilities

Games
Game Interviews
Game Reviews

Hardware
Headphone Reviews
Sound Card Reviews
Speaker Reviews

Help
FAQ
Joysticks
Vortex 1
Vortex 2
Vortex Advantage

Links
Audio Links