Audio

Prey, according to the guys at Human Head Studios, has been designed with Creative's X-Fi in mind from the get go. This makes it interesting to us, as it's one of the games that will make the most of the enthusiast audio card.

To make the most of X-Fi, you'll need to go and grab the latest driver from the Creative site, which includes the optimisations for Prey. The game uses the OpenAL architecture which Creative supports and builds on top of. In-game, you only have the choice of stereo, standard 5.1 or OpenAL.

Features

The OpenAL driver allows for positional audio, and this is critical to the gaming experience. So much of your time in Prey, especially in multiplayer, is spent on the ceiling or on the wall, that maintaining a sense of direction can be incredibly hard. Good positional audio really helps you say oriented.

On top of the basic OpenAL model, Creative's software team added EAX features on top of this. The X-Fi supports up to four simultaneous reverbs in this game, which are used to add better positional cues to sound and help orientate the player. Creative actually replaced all the reverbs that 3DRealms originally created. There are also obstruction and occlusion effects, which means that sounds behind doors and portals sound muted. As the player leaves the 'real world' into the 'spirit world', sounds from the real world are low-pass filtered so that they're still audible, but are rather ethereal. It's an awesome effect.

Technicalities

The game stores all the sound data as compressed OGG files. In normal gameplay, the sound is decompressed into memory on the fly, using up CPU time. If you have an X-Fi board that supports X-RAM, the sound data can be decompressed at the start of the level and handled by the onboard processor, freeing up CPU cycles for gameplay.

The default audio mixer outputs at 44.1khz, whereas the OpenAL mixer outputs at 48khz, making for better audio quality. The OpenAL mixer also avoids fixing the audio into a speaker configuration until the final playback stage, which means the audio hardware can have a say in how the audio is positioned, based on control panel settings. This allows effects like headphone 3D to be utilised a lot more convincingly, leading to better surround sound quality.

The standard mixer supports up to 127 voices, but these are mixed right down when it comes to playback. With X-Fi, you can have 124 voices playing simultaneously. When would you ever have 120+ sound effects in game? With Prey, actually quite often. One of the introduction scenes sees you getting straight up to more than 110 voices, and firing a gun can often produce twenty or so, once you've taken into account the environmental effects.

In-game testing

We played through part of the game with the default mixer using onboard audio, then using an X-Fi Fatal1ty card with the OpenAL and EAX effects to see if it made much of a difference to our gameplay experience.

Number one is that we didn't really see a performance difference between the two. The framerate for two sections that we benchmarked was almost identical using the standard mixer and the OpenAL mixer. This rather proves to us that the X-Fi is doing its task of handling the better quality audio without having to ask for CPU time.

The sound quality using the OpenAL mixer was definitely better - we were able to hear a noticeable difference. Environmental audio effects added a subtle twang to sounds, and one of the first introductory sequences, as our heroes are carried through the bowels of a space ship accompanied by the screams of those captured, was given a horrific new effect by the added positional audio and occlusion.

We also found that we were more readily able to track our enemies in multiPrey, which was a bonus given our otherwise rather lacking skills.

The differences are sometimes subtle, but noticeable to those that really care about audio - which, we suppose is rather the point. Our only complaint is that we found that the positional audio panning was sometimes overly aggressive, moving sounds a little too quickly between headphones when using the CMSS 3D Headphone effect.