Itâ€™s also worth emphasising that for the first time since the Live! cards, the clock rate can run at 44.1kHz without the need for re-sampling. This was always a major complaint from audio developers and now means that card is free to run at 44.1 or 48KHz (as well as higher rates) when using the musician-focused ASIO drivers.
Using Unreal Tournament 2004, turning on 3D audio and EAX effects results in a small dip in frame rate. Running the same demos but using the onboard Avance AC97 chip actually resulted in a slightly higher frame rate although it would only be using EAX 1 level of effects and not EAX 4 Advanced HD.
Claims that the cards can increase the speed that games play at are no doubt true but will be dependent on the actual game being benchmarked, the level of EAX and whether the X-Ram (where available) is specifically being addressed.
One of the features that seem to have most impressed in the previews is the updated CMSS-3D feature. Its abilities include altering stereo content to make it appear as if itâ€™s being played across a wider sound-stage when using headphones or stereo speakers, and when using a surround set up, extracting surround information and intelligently playing it across speakers.
CMSS-3D as an effect is based on Head Related Transfer Functions (HRTF). This is one of the main techniques through which our brains decode the spatial placement of sounds. As the sound enters the ears, the frequency content of the sound is altered through interference with the shape of the outer ear; the frequency pattern is obviously dependent on where the sound source is located and therefore the path being travelled to the ears.
The alterations in frequency can be measured by using a dummy head with microphones placed in the â€˜earsâ€™ and recording a known sound or frequency. HRTF based effects are always the most dramatic when using headphones, as the placement of the listener in relation to the speakers (or headphones) is exactly known and thereâ€™s little chance of the sound from one side interfering with the other.
Using this technique, as the individual sounds in a 3D environment move around, they can be processed in real time with these HRTF impulses, simulating the processing that your ears would normally do. This is a great way of making the sounds appear from all around the player with only a regular set of headphones.