Prey™ is proving to be one of the year's biggest first person shooters. In addition to featuring stunning graphics that are based on a modified Doom 3 engine, Prey is also heavily optimized to take advantage of the hardware accelerated audio features of Sound Blaster X-Fi. By harnessing the massive processing power of Sound Blaster X-Fi, you'll be able to utilize all the advanced audio effects with no impact on your frame-rates!

Default Mixer
By default the game will start up using the "Default Mixer" in stereo mode. The more advanced "OpenAL Mixer" can only be enabled if the audio device supports at least EAX^® ADVANCED HD™ 4.0 and has the latest audio drivers installed.

OpenAL Mixer
If a supported card is installed and yet the OpenAL option cannot be selected the user may not have the latest drivers. The user should therefore visit www.soundblaster.com and update their drivers. Prey will also prompt you to go to the Creative website to get the latest drivers.

Due to the tight integration in the hardware audio implementation between OpenAL and EAX ADVANCED HD, other audio solutions, such as the Realtek onboard audio and nVidia nForce motherboard audio, will only be able to run the "Default Mixer".

One of the key points to note with Prey is that it uses a lot of audio channels. For example if you are standing alone in the Multiplayer map DMSavagewalk and you fire the starting gun the channel count will already be as high as 28 channels. One can imagine what the count would be with more than one player all strafing the map. Now consider the impact of all those sound channels with the voice-limited onboard audio based system which can only support up to 32 channels!

In one of the intro animation sequences (Roadhouse.map) where the alien ships are tearing up the bar, audio usage can easily jump to over 110 channels. The Sound Blaster Audigy 2 ZS, for example, would be constantly maxing out its 64 channels. This means that certain sounds will have to be dropped due to lack of voice resources. The Sound Blaster X-Fi does not have this problem, since it supports 128 channels.

Prey uses EAX ADVANCED HD to perform per source occlusion to accurately model the opening and closing of doors and portals. It checks to see whether or not there is a closed door or portal between the player and the sound and if so, it does a really cool occlusion effect on those sounds. It can even take into account how many closed doors are between the player and the sound, and add more or less sound effects accordingly. You can try this by lobbing a grenade through a door just before it closes and listen to the explosion. Next, step a bit closer to the door so that it does not close, and lob a grenade through the same door and listen to the difference.

 

Prey Environment Effects

One of the most subliminally impressive parts of the Prey audio implementation is the EAX ADVANCED HD environment effects. These truly add a life-like and in some cases terrifying aspect to the gameplay.

You will notice that as you play through Prey each of the environments have had different environment effects applied. From metallic echoes in small rooms to deep reverbs in large halls these environment effects add another dimension to the gameplay that once experienced becomes a requirement for future sessions!

Getting Audio Information from Prey

There are a few commands that can be used to get some interesting information on how audio is being used and managed during gameplay. Below we show the console commands that allow you to get access to this information:

• Open the console by pressing and ~ and type "listActiveSounds" to see the channel usage (only when using the "OpenAL Mixer"):

You will see the following information:

using XXX mono OpenAL sources
using YYY stereo OpenAL sources

On a Sound Blaster X-Fi based card (i.e. 128 channel capable card) the maximum number of stereo sources is 16 and the maximum number of mono sources is 92.

On a Sound Blaster Audigy 2 ZS (i.e. 64 channel capable card) the maximum number of stereo sources is 8 and the maximum number of mono sources is 44.

On other OpenAL audio devices (i.e. 32 channel capable card) the maximum number of stereo sources is 4 and the maximum number of mono sources is 21.

Basically, the voices are scaled to match the playback capabilities of the audio device. Running more than 28 channels on a host-based audio system would dramatically affect the performance of that PC. The stereo sources in particular are critical because they are used mainly for the firing sounds made by the player and a few ambient sounds.

• Open the console again ( and ~) and type "listSounds" to see memory and X-RAM usage (only when using the "OpenAL" sound system):

You will see the following information:

AAAA total samples loaded (Total amount of samples loaded for this map - multiply by two to get bytes)
BBBB kB OGG samples loaded (Total amount of OGG compressed sample data loaded for this map)
CCCC kB PCM samples loaded (Total amount of PCM uncompressed sample data loaded for this map)
EEEE kB total OpenAL memory used (Total amount of sample data, both compressed and uncompressed, in OpenAL buffers)
FFFF kB total onboard memory used (Total amount of X-RAM in use)

For example if you run the level called "Roadhouse" and type the above command you will see the following data (table shows comparison between Sound Blaster X-Fi XtremeMusic card vs. Sound Blaster X-Fi Fatal1ty.

You will note that there is a figure of 2048 shown for the "kB total onboard memory used" in the Sound Blaster X-Fi XtremeMusic column. This is because this card has 2MB of RAM hardwired for DSP effects processing and this command simply highlights the memory in use on the card.

Related articles:

Mind-bending Audio in Prey™
Interview with Ed Lima, Audio Lead for Prey

 Hardware Accelerated Audio in Prey™
An in-depth look at the Sound Blaster X-Fi technologies featured in Prey