Dolby Digital is an encoded compressed digital signal. It’s easy to forget that Dolby Digital is compressed, the original intention to include up to six channels (front stereo, centre, rear stereo and sub-woofer) using the equivalent bandwidth of a standard uncompressed stereo signal. While it uses a similar technique to mp3 compression, as it’s a newer and more sophisticated technology the compression artefacts are far less obvious, particularly if listening to a film or game rather than music. The promotional material emphasises the benefits of using a digital connection to the amp, including cutting out noise and interference coming from the audio cables. In my experience noise from cables is less of a problem than the interference picked up by the analogue connections on the card from the PC itself. Sure enough using the digital connection helps clean this up substantially.
The maximum number of channels that Dolby Digital Live can output is 5.1, the 7.1 features of the card only relate to its analogue outputs. This seems like a missed opportunity to the two features to complement each other, but I guess it’s a limitation of Dolby’s technology rather Terratec.
That said, I’ve yet to be convinced of the merits of including 7.1 on a budget consumer soundcard (there’s an interesting article on the usefulness or otherwise of 7.1 here. With so little 7.1 encoded material available it makes much more sense to spend the money on a higher quality 5.1 speaker system which will be more than adequate for all but the largest of living spaces. This card doesn’t have ASIO drivers so those eight channels can’t be addressed by any music software you may be running.
The card itself sports as many connections as is physically possible to include within a single PCI bracket. They include a microphone and line input, four stereo outputs and a S/PDIF input and output (which has the Dolby Digital Live).
In terms of features beyond Dolby Digital, you get the usual EAX 2 support. Whilst the chip on the card mentions support for HRTF, or virtual surround, there was no obvious way of turning this on, unlike other Terratec cards, and using the positional software test that forms part of the Right Mark 3D Sound test didn’t reveal any difference when the sound is placed behind the listener.