Otherwise known as the CMI8788, the Oxygen HD supports resolutions and sampling rates up to 32 bits and 192kHz across eight channels. More importantly, the Oxygen HD's feature set includes the ability to encode Dolby Digital Live and DTS, allowing it to produce multi-channel digital output via a single S/PDIF connection rather than a mess of analog cables—a capability not even Creative's vaunted X-Fi can match.
Of the handful of manufacturers building sound cards with the Oxygen HD, Auzentech and Sondigo have the most divergent approaches. Sondigo's Inferno is a basic implementation of the Oxygen HD that takes full advantage of the chip's capabilities but doesn't really push the envelope on features and extras. Auzentech's X-Meridian is a little more exotic, with a focus on output quality and flexibility that goes so far as to allow users to swap out onboard chips. Keep reading to find out which of these implementations we prefer and whether either can challenge the X-Fi's mix of features, performance, and sound quality.
C-Media's Oxygen HD
Since the X-Meridian and Inferno use the same Oxygen HD CMI8788 audio chip, that seems like a good place to start. The Oxygen is the latest in a long line of C-Media audio processors, and its feature set is pretty stacked. In total, the chip supports a whopping 12 output channels and eight input channels. The output channels are split between three groups: the first group handles eight-channel output at up to 32 bits and 192kHz, the second provides two-channel S/PDIF output at up to 32 bits and 192kHz, and the third offers two-channel audio for front-panel connections at up to 16 bits and 48kHz. On the input side of the equation, you get eight channels, all at up to 32 bits and 192kHz.
With the exception of digital S/PDIF connections, the Oxygen HD's input and output ports have to undergo digital to analog conversions. That's done on external chips, and as luck would have it, the Auzentech and Sondigo cards we'll be looking at today use the same digital-to-analog converters (DACs). Both cards employ AKM AK4396VF DACs, capable of supporting analog output at up to 24 bits and 192kHz. 24-bit audio is pretty much the standard for mastering and high-definition content like DVD-Audio, so it's no surprise that the cards don't exploit the Oxygen's support for 32-bit resolutions.
Apart from sampling rates and resolutions, the Oxygen's feature list is loaded with buzzwords. The DTS NeoPC and Dolby Pro-Logic IIx standards, allowing users to upmix stereo content for output on 7.1-channel speaker setups. Going in the opposite direction, Dolby Virtual Speaker support allows for virtual surround sound from just two speakers. Dolby Headphone provides similar functionality through headphones, creating a virtual surround sound experience that won't wake your neighbors.
Up- and down-mixing stereo and multi-channel content for different speaker configurations isn't terribly unique—sound cards, including the X-Fi, have been doing that for quite some time now. However, the Oxygen does have a couple of aces up its sleeve in the form of integrated DTS and Dolby Digital Live encoders.
Normally, running a multi-channel speaker setup requires at least three analog cables—one for each of the front, rear, and center/sub channels. However, DTS Interactive and Dolby Digital Live allow that multi-channel input to be transferred over a single digital S/PDIF connection. You'll need a receiver or speaker system that supports DTS or Dolby Digital Live decoding, but most high-end options do. Even Logitech's older Z-680 speakers can accept DTS and Dolby Digital Live input.
What makes the Oxygen's DTS and Dolby encoders particularly useful is that they can take any multi-channel audio stream—be it from a video file, DVD, or even a game—and convert it to digital output in real-time. Competing sounds cards like Creative's X-Fi are capable of multi-channel digital output, but they can't do encoding on the fly, so they're only capable of passing along an encoded bitstream that already exists. That works fine for DVD movies and audio discs equipped with pre-encoded DTS tracks, but it doesn't fly with games, where you have to fall back to analog output to get multi-channel sound.
The ability to enjoy multi-channel surround sound in games over a single digital connection is a coup for the Oxygen HD, but otherwise, the chip actually isn't all that well-equipped for gaming. The chip offers no hardware acceleration for positional 3D audio, and its EAX support tops out at version 2.0, which limits the number of concurrent 3D voices to just 32. These days, EAX goes all the way up to version 5.0, which supports up to 128 concurrent 3D voices and higher sampling rates and resolutions. To be fair, the Oxygen HD isn't alone in its lack of support for advanced EAX levels and hardware accelerated positional 3D audio. Creative's the only game in town if you want those features.
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