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Asus' Xonar DX sound card

High-end audio on a diet

Manufacturer Asus
Model Xonar DX
Price (Street) $89.99
Availability Now

I used to date a girl who was a little obsessive about what she ate. At every opportunity, she would buy fat-free, low-calorie, or otherwise diet derivatives of common food items. Now there's nothing wrong with foods that are naturally fat-free or low in calories, but when you strip out the fat, salt, sugar, and delicious-but-carcinogenic chemicals, something is usually lost in the translation. Fat-free ice cream, for example, lacks the all-important creaminess that fat provides. Unsalted potato chips fall flat precisely because they lack salt. And Diet Coke, well, that just tastes wrong.

Diet versions of existing products tend to be hollow representations of the originals, so we were understandably a little cautious when Asus announced its new Xonar DX sound card. The PC hardware giant stormed onto the sound card scene with the Xonar D2X just a few months ago, putting longtime market magnate Creative on notice. A $180 asking price put the D2X firmly in luxury territory, but with PCI Express connectivity, high quality components, innovative features, and useful bundled extras, it's definitely worth the price—especially when you consider the card's solid gaming performance and exceptional sound quality.

Asus' new Xonar rings in at half the cost of the D2X, and the card itself is half the size. Naturally, then, the DX is missing some of the features and extras of its full-fat cousin. Keep reading to see how the diet Xonar fares without them.

The Xonar, sans frills
The Xonar DX differs from its D2X cousin in many ways, but some of those differences are more important than others. Take the audio chips used in each card, for example. The DX employs what's marked as an Asus AV100 audio processor while the D2X uses an AV200. Don't pay too much attention to the names silk-screened onto the chips, though; they're the very same C-Media Oxygen HD audio processor under the hood. Asus says the chips go through a "quality sorting" process to separate the AV100s from the AV200s.

Asus Xonar D2X Asus Xonar DX
Audio chip Asus AV200 Asus AV100
Digital-to-analog converter TI Burr Brown PCM1796 Cirrus Logic CS4398 (front)
Cirrus Logic CS4362A (center, rear, side)
Analog-to-digital converter Cirrus Logic CS5381 Cirrus Logic CS5361
Maximum recording quality 24-bit/192kHz 24-bit/192kHz
Maximum playback quality 24-bit/192kHz 24-bit/192kHz
Signal-to-noise rating 118dB 116dB (front)
112dB (center, rear, side)
Output channels 7.1 7.1
Multichannel digital output Dolby Digital Live, DTS Dolby Digital Live
Interface PCI Express x1 PCI Express x1
Street price $89.99

The Xonar DX's AV100 audio processor may differ from the AV200 in name only, but that's not the case with the card's other onboard components. The DX uses a combination of Cirrus Logic CS4398 and CS4362A digital-to-analog converters to feed its analog output ports. The CS4398 is in charge of the card's front output channels, and with a signal-to-noise rating of 120 dB, it's the higher-quality of the two. Center, side, and rear channels are handled by a CS4362A chip that carries an SNR rating of only 114 dB. For reference, the TI Burr Brown DACs used for all of the Xonar D2X's output channels carry a 123 dB SNR rating.

Going in the opposite direction, from analog to digital, both Xonars feature ADCs from Cirrus Logic. The cards use different chips, though, with the DX featuring a CS5361 to the D2X's CS5381. Signal-to-noise ratings once again favor the D2X. The CS5381 is rated for 120 dB, while the CS5361 has a rated 114 dB SNR.

Individual parts specs are important, of course, but we're more interested in the Xonar DX as a sound card. Asus pegs the card's overall signal-to-noise rating at 116 dB for the front outputs and 112 dB for the rest. That's reasonably close to the 118 dB SNR rating of the Xonar D2X, especially if you're mostly going to be listening to stereo content.

Despite differences in SNR, both cards support high-definition audio at up to 24 bits and 192kHz across all their inputs and outputs. Support for 192kHz recording is particularly notable because Creative's X-Fis can only record at up to 96kHz.

Like most modern sound cards, the Xonars feature 7.1 analog output channels. Their Oxygen HD audio chips are also capable of encoding Dolby Digital Live bitstreams in real time. Support for real-time Dolby Digital Live encoding is useful for folks who want to play games on multi-channel speakers using a digital output. Running multi-channel output through a single digital connection is much neater than using a bunch of analog cables, although you will need a compatible receiver or set of digital speakers capable of decoding a Dolby Digital Live signal.

In addition its ability to encode DDL bitstreams on the fly, the Oxygen HD audio chip can also do real-time DTS Interactive encoding. This DTS encoding capability doesn't make the cut for the Xonar DX, though; it's only exposed in the pricier D2X model. DTS Interactive and Dolby Digital Live perform the same function, so the only thing the Xonar DX really loses here is compatibility with receivers or digital speakers that support the former but not the latter.

While it's not listed in the chart, we should note that the Xonar DX retains the D2X's support for Dolby Headphone and Virtual Speaker, er, virtualization schemes that simulate 5.1-channel environments over stereo output. Dolby Pro-Logic IIx is also on the menu for those who want to up-mix stereo or 5.1-channel content for output across 6.1 or 7.1 channels.

A creative approach to EAX support
Perhaps the greatest weakness of the Oxygen HD audio chip used in the Xonar DX is its relatively pedestrian positional 3D audio credentials. The chip natively supports EAX 2.0—a technology that dates back to the SoundBlaster Live! and is restricted to 32 concurrent 3D voices. Creative's latest X-Fis can handle up to 128 concurrent 3D voices at higher definition sampling rates and resolutions. The X-Fi also performs positional audio calculations in hardware, while the Oxygen HD has to offload them to the host system's CPU.

The popularity of multi-core processors (and more importantly, games that leave multiple cores unused) has lessened the need for hardware-accelerated 3D audio, but there's still a big gap between EAX 2.0 and 5.0. Asus bridges that gap with a software feature it calls DirectSound 3D GX 2.0, which is capable of emulating EAX 5.0 functionality that had previously only been available with Creative's X-Fi cards.

DS3D GX presents the Xonar as an EAX 5.0-compliant audio card, and then intercepts EAX calls, re-routing them to the Xonar's own audio processing engine. That engine does its best to approximate EAX effects, and it can handle up to 128 concurrent 3D voices with enhanced reverb effects for "most" DirectSound 3D games. Positional audio calculations are still performed on the host system's CPU, but DS3D GX at least brings the Xonar beyond EAX 2.0's 32-voice limitation.

Creative is quick to point out that DirectSound 3D GX doesn't deliver "genuine" EAX 5.0 effects, and Asus readily admits as much. However, Asus also says users will be hard-pressed to tell the difference between the two—a claim we'll explore when we dive into listening tests a little later in the review.

Asus cites an additional advantage of its DS3D GX approach for Windows Vista users. Vista features an all-new Universal Audio Architecture (which you can read about in more detail in our initial look at the Xonar D2X) that removes the hardware abstraction layer for DirectSound 3D, effectively killing positional 3D audio in games that exclusively rely on DirectSound 3D and its EAX extensions. To work around the new audio stack, Creative offers an ALchemy software package that converts DirectSound 3D calls for processing by a third-party OpenAL API that still has direct access to audio hardware in Vista.

Thus, at least in Vista, ALchemy performs a similar function to DirectSound 3D GX. However, ALchemy is a standalone application that must be specifically configured to work with different games. DS3D GX is built right into the Xonar's drivers and doesn't require additional software or game-specific profiles.