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Asus' Xonar DG and Xense sound cards

Do you really need discrete audio?
— 11:22 PM on November 21, 2010

When building a new PC, today's enthusiast faces numerous important questions. How many CPU cores do I need? Will a GeForce or a Radeon deliver the smoothest frame rates in the games I play the most? Can I afford a solid-state disk large enough to be useful as a system and applications drive? How quiet can I make the rig without sacrificing performance? Oh, and do I really need a sound card?

I bet you can tell where this is going.

Not too long ago, the answer to that last question would have been a unequivocal yes. There was a time when the "free" audio integrated on motherboards was almost universally horrendous. Early onboard sound implementations were plagued by poor-quality codecs and board-level interference that translated to lousy audio quality. They also lacked hardware acceleration for positional 3D audio, which was a big deal at the time.

Fast-forward to today, and the PC audio landscape has changed dramatically. Creative's EAX positional audio standard is all but dead, and the rise of console ports seems to have squelched the need hardware-accelerated 3D audio entirely. Onboard solutions have gotten better, too, causing many to claim that modern implementations are more than adequate for most users. Some defend this position with the sort of passionate ferocity normally reserved for GPU flame wars. I'm not so sure, though.

You see, as integrated audio has improved, so have discrete sound cards. The iconic Sound Blaster may be stagnating, but other players are picking up the slack, notably Asus, whose family of Xonar sound cards has been growing faster than the Duggars. Asus first waded into the sound card market with the Xonar D2X, an ambitious high-end model that garnered a TR Editor's Choice award on its maiden voyage. Now, some three years later, Asus is celebrating the Xonar's anniversary with a new model dubbed the Xense. Bundled with a gaming headset from Sennheiser, the Xense has all the trappings of a fancy sound card: high-quality DACs, replaceable OPAMPs, 1/4" jacks, a headphone amp, and support for multichannel analog and digital output. At $280 online, it's definitely a luxury item, perhaps too big a step up for someone unsure whether they even need a sound card.

Fortunately, the Xense isn't the only fresh addition to the Xonar lineup. Asus has also rolled out the Xonar DG with a much more affordable $30 street price. The DG isn't nearly as indulgent as the Xense, but its low cost gives us the perfect opportunity to explore what even a modest audio upgrade can do for a PC otherwise relying on an integrated Realtek codec. So we have, and we've thrown the Xense into the mix to see whether it's worth the additional expense. Keeping reading to find out.

Much more than an audio codec
When integrated on a motherboard, audio is usually handled by a single codec chip. Apart from the processing done in software by an associated driver, this lone piece of silicon is responsible for translating binary bitstreams into something that can be output to your speakers or headset. That's quite an important role, but as is too often the case, motherboard makers tend to opt for the simplest and cheapest implementation that will get the job done. I understand their dilemma, at least to some extent. Audio must compete with other peripheral chips in a world where board real estate is at a premium, and it's not really as sexy as USB 3.0 or 6Gbps SATA.

Obviously, discrete solutions have a natural advantage. Not only do they get to focus solely on delivering quality sound, they can also spread out on an expansion card. With plenty of room to breathe, sound cards are free to tackle tasks that would otherwise be performed by a single audio codec with a small army of chips and auxiliary components.

An audio processor is at the center of this web of additional hardware, and the market is currently dominated by two camps: Creative's X-Fi derivatives and the various flavors of C-Media's Oxygen HD. The latter is favored by Asus, which sometimes hides an Oxygen under silk-screening bearing its own name. Such is the case with the Xense, whose "Asus AV100" audio processor is, in fact, a C-Media CMI8788. We first encountered this Oxygen HD chip in early 2007, and it's been around the block a few times since. The fact that the CMI8788 is still relevant is a testament to just how little the PC audio market has moved in the last few years.

Audio standards haven't really budged since the chip's introduction, for example. The Oxygen HD is capable of handling 24-bit resolutions at sampling rates up to 192kHz, which is as high-definition as consumer audio gets. With eight output channels, the C-Media chip is also equipped to feed elaborate 7.1-speaker home-theater setups. To this formula, Asus adds surround-sound speaker virtualization via Dolby Headphone and the ability to encode multichannel digital bitstreams on the fly with Dolby Digital Live.

For folks who play older games that make use of EAX effects, Asus has also implemented GX2.5, the latest version of its EAX emulation scheme. GX2.5 can juggle up to 128 simultaneous positional audio effects, which is as many as are available with Creative's latest version of EAX. To give you a sense of how old that standard is, the last revision, EAX 5.0, debuted with the original X-Fi more than a half-decade ago.

Asus declined to add its own name to the audio processor that graces the Xonar DG, although the company informs us that this CMI8786 is a custom order. The chip has Oxygen HD heritage and can be best thought of as a cut-down version of the CMI8788. 24-bit audio is still supported, but only at sampling rates up to 96kHz. The number of output channels has been reduced to six, and there's no provision for real-time multichannel encoding for digital output. However, Dolby Headphone is still included, and so is GX2.5. Folks using analog speakers or headphones aren't likely to need much more.

Of course, the audio processor is only responsible for sound when it's expressed in ones and zeroes. The DACs tasked with translating digital audio into an analog signal can make or break a card's output quality, at least with the sort of speakers and headphones most plug into their systems. On the Xense, a "Burr Brown" stereo DAC from Texas Instruments handles the front-channel out, while a Cirrus Logic chip takes care of the rest of the outgoing channels. Cirrus logic is also responsible for the Xense's ADC, which takes care of digital conversions for the card's analog input.

Xonar DG Xonar Xense
Interface 32-bit PCI PCI Express x1
Audio chip C-Media CMI8786 Asus AV100
Digital-to-analog converter Cirrus Logic CS4361 Texas Instruments PCM1796
Cirrus Logic CS4362A
Analog-to-digital converter Cirrus Logic CS4245 Cirrus Logic CS5381
Headphone amp Texas Instruments DRV601RTJR Texas Instruments 6120A2
Replaceable OPAMPs? No Yes
Maximum recording quality 24-bit/96kHz 24-bit/192kHz
Maximum playback quality 24-bit/96kHz 24-bit/192kHz
Output signal-to-noise ratio 105 dB 118 dB
Input signal-to-noise ratio 103 dB 118 dB
Output channels 6 8
Multi-channel digital encoding NA Dolby Digital Live!
Speaker virtualization Dolby Headphone Dolby Headphone
Street price $30 $280

Things are a little simpler on the Xonar DG, whose analog outs are fed solely by a Cirrus Logic DAC—one with a 104-dB signal-to-noise ratio that's is notably lower than that of the Texas Instruments and Cirrus chips on the Xense, which are rated at 123 and 114 dB, respectively. I suspect the DG's Cirrus Logic ADC isn't quite as good as the one sitting on the Xense, either, although we'll be able to get a sense of things with some "loopback" audio tests a little later in the review. For what it's worth, Asus pegs the Xense's overall output and input SNR at 118 dB, while the DG's outputs are listed at 105 dB and its input at 103 dB.

Built-in headphone amplification is something you won't find on a motherboard, but it's featured in both Xonars. On the DG, Asus has gone with Texas Instruments' DRV601RTJR, which is optimized for headphone impedances of 32-150 Ω according to the card's spec sheet. The Xense gets something considerably fancier: a TI amp capable of pushing headphones with impedances up to 600 Ω. Of course, the headphones bundled with the card are rated for an impedance of only 150 Ω. Mid-range stereo cans like Sennheiser's excellent HD 555s, which we use for listening tests, have a rated impedance of just 50 Ω. You don't need big numbers for high-quality sound.