Of all the products I've reviewed for TR in the last year, Asus' Xonar DG has to be one of my favorites. We've long lauded the benefits of discrete sound cards for anyone with an appreciation for high-fidelity audio, and the DG is a pretty exceptional example of the breed. The card couples superb analog output quality with Dolby speaker virtualization technology and a shockingly low $30 asking price, making it the best bargain in PC audio since the Chaintech AV-710. No wonder this Editor's Choice winner has become a new staple of our TR System Guide.
Although the Xonar DG is a no-brainer for anyone still using the analog audio jacks on their motherboard, you'll need a free PCI slot to add one to a system. That rules out some configurations, including small-form-factor HTPCs and gaming rigs. Notebooks can't play, either, and their built-in audio can be particularly poor. So, when Asus described its latest Xonar U3 as a USB version of the DG, you can understand why we got a bit excited.
At 3.1" x 1.2" x 0.57", the U3 is small enough to be a choking hazard. The thing weighs just 25 grams, making it barely noticeable in your pocket. I wouldn't have minded something a little heavier, though. When combined with the plastic body, the lightweight U3 feels a little, well, cheap.
Maybe that's my disdain for glossy plastics talking. Or maybe it's the U3's around $40 asking price. In any case, the shiny black finish is yet another fingerprint magnet, and it comes from a company that we thought had learned its lesson with notebooks. A textured or matte exterior would be far more appropriate for something that's likely to be handled with frequency. If I had my way, the U3 would be wrapped in a sturdy layer of brushed metal.
The U3 does have a flash of aesthetic flair in the form of two LED-backlit accent grills. Thankfully, the blue LEDs glow softly when the U3 is plugged in, and the grill diffuses much of the light they emit. No blinding here.
Want a hint about how good the U3 sounds? I couldn't bear to fracture the plastic body to snap pictures of the hardware inside. The underlying audio processor is an Asus UA100 based on a C-Media chip. Every Xonar we've seen has used variations of C-Media silicon, and this particular example has been tuned to Asus' specifications. Among the modifications: a little extra "pop" for vocals and percussion, an attribute we found quite pleasing to the ears on the Xonar DG.
The UA100 incorporates DAC and ADC components, so separate chips aren't required to handle converting audio between analog and digital formats. Unfortunately, the UA100 only supports resolutions and sampling rates up to 16 bits and 48kHz, respectively—standard-definition audio, in other words. HD audio is rare outside of Blu-ray movies and DVD-Audio discs, but a lack of support for it is nonetheless notable. C-Media's CM6600 USB audio processors all support 24-bit/192kHz audio, suggesting that the UA100 is based on the older CM6400 series.
With a native USB interface, the UA100 doesn't need a bridge chip to interface with a host system. Asus has, however, incorporated the same Texas Instruments DRV601RTJR headphone amplifier used in the Xonar DG. The headphone amp makes a lot of sense given the U3's notebook aspirations; virtually all of the audio that comes out of my notebook is fed through a pair of headphones.
Removing the U3's plastic cap reveals a male USB plug and little else of note. A thin leash ensures that you won't lose the cap, which can always be taken off entirely. Having the extra piece jangle around is a little annoying, making me wish the U3 used some kind of slider mechanism to protect its lone appendage.
When plugged into a system, the U3 becomes the appendage. Separating analog audio signals from system-level noise is part of what helps discrete solutions sound better than integrated solutions. With a PC expansion card, you're lifting audio hardware away from the hum of activity on the motherboard. The Xonar U3 does one better by taking everything outside the chassis completely.
To further reduce noise interference, the U3 features a "Hyper-Grounding design" that Asus says is the key to its sound quality. This Xonar-exclusive feature isn't found on competing USB audio solutions, the firm claims.
Like most notebooks, the U3 has only two audio ports: a headphone/line output and a microphone/line input. The headphone jack doubles as a digital S/PDIF output with the aid of a TOS-Link adapter that's included in the box.
If you're in the mood for a surround-sound experience that extends beyond two-channel stereo output, the U3 employs virtualization schemes for headphones and speakers. This software-based simulation system comes courtesy of Dolby, which also provides real-time encoding for multi-channel digital audio output via Dolby Digital Live. You don't get the same on-the-fly encoding tech with the Xonar DG, making its inclusion in the U3 especially notable. Most modern notebooks can pass immaculate multi-channel bitstreams to compatible receivers via their HDMI outputs (motherboards can do the same via their S/PDIF outs), but that generally only applies to content with pre-encoded audio tracks, such as movies. Getting multi-channel digital output with games requires real-time encoding.
Despite its compact dimensions, the Xonar's plastic body still has the potential to complicate access to adjacent USB ports. The casing extends 9 mm to the right of the USB plug and 12 mm to the left, resulting in a tight fit on my Acer ultraportable. The Xonar is slimmer than it is wide, with the plastic shell reaching 6.5 mm above the USB plug and 4.5 mm below it.
Asus seems to realize that clearances might be an issue for some folks, because it includes a short USB extension cable in the box. A driver CD rounds out the extras, which are expectedly spartan for what amounts to a budget product.
On the driver CD, you'll find the same Xonar software Asus ships with its other sound cards. There are plenty of settings to tweak, including three gain modes for different headphone impedance ranges. This is also where one can enable speaker virtualization and surround-sound encoding.
Like other Xonars, the U3 is capable of emulating EAX 5.0 effects using a software layer dubbed GX 2.5. Up to 128 positional audio effects can be processed simultaneously. That said, it's rare to find EAX effects in modern games. Developers have largely abandoned Creative's positional audio standard in favor of cross-platform solutions that work with consoles.
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