In Windows Vista, Microsoft has decided to remove the Hardware Abstraction Layer (HAL) for DirectSound and DirectSound3D. The HAL is the software layer that on previous Windows Operating Systems enabled an audio accelerator such as the SB X-Fi, to provide DirectSound3D applications with hardware accelerated audio. This enabled soundcards to perform tasks such as sample-rate conversion, mixing, 3D spatialization using HRTFs, filtering, and effects processing. Without the HAL, DirectSound on Windows Vista will be rendered in software with no advanced functionality such as EAX.
The audio changes in Windows Vista do not affect OpenAL however. For audio cards that feature 'native' OpenAL support, SB X-Fi series of cards, there is no need to worry! Games that enable support for OpenAL will continue to run just as they do on Windows XP - with hardware accelerated audio and effects.
Although OpenAL has arguably replaced DirectSound3D, particularly in many modern PC Games (e.g Battlefield 2142, Doom3, Quake 4, Prey, etc ...), there are hundreds of older PC games that support DirectSound3D and EAX technology --- all of these games will sound empty and lifeless on Vista. As most DS3D games only enable 3D Audio (and EAX) if a hardware accelerator is present, most of these games will be reduced to a stereo output.
The good news is that the Creative ALchemy Project allows you to run your favorite DirectSound3D games on Windows Vista as the developers intended - with full hardware accelerated 3D Audio and EAX support! This is done by translating DirectSound calls into OpenAL. In order for this to happen, a couple of files need to be installed into each game directory. This is handled automatically by the ALchemy installer - but can also be performed manually by advanced users.
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