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ASUS Xonar D2 Sound Card

Date: September 3, 2007
Author(s): Rory Buszka

At Computex 2007, ASUS wowed us with their new Xonar range of audio products, aiming to take a chunk of Creative’s market share in the high end PC audio category. Now we’ve got our hands on the ASUS Xonar D2, and we’re putting it to the test. Does the newcomer Xonar D2 have what it takes to challenge the X-Fi?


At Computex 2007, one of the more surprising new products was ASUS’ visually-striking Xonar family of sound cards. This is new ground for Asus, who is better known for their motherboards, video cards, displays, and laptops. However, a sound card from ASUS is huge news, because ASUS products are well known for targeting the high end market, and delivering both a rich feature set and outstanding performance.

As unexpected as ASUS’ move into PC audio hardware was, in a way it makes perfect sense for the company. After all, high-quality audio is centrally important to a compelling media experience, and discrete sound solutions provide an essential upgrade in clarity, impact, and quality over the onboard audio solutions found on many motherboards. Those onboard solutions are usually intended for office PCs and workstations, and rarely deliver a satisfying performance in gaming and media center applications.

The new Xonar family currently contains three products, the D2 and soon-to-be-released D2X desktop audio cards, and the U1 external USB audio station. The D2X product is essentially the same as the D2 in features and capability, but it uses a PCI-Express 1x interface, which at last gives you something meaningful to use your motherboard’s 1x PCIe slots for. We decided to pass on the D2X, however, because we HAD to be one of the first to take this new card for a spin, so we settled for the D2 with its PCI interface.

The Xonar D2 bears more than just a passing resemblance to Razer’s Barracuda AC-1 sound card, which we reviewed earlier this year. This is thanks in part to the steel “EMI Shield” that covers the majority of the card. Its most dominant visual feature is a large ring in the center that glows yellow when powered up. The purpose of the EMI shield is more than purely cosmetic, however, as I’ll explain later.

The Xonar cards also feature black PCBs, in keeping with ASUS’ current use of black PCBs on their enthusiast motherboards, and plenty of gold plating to dazzle the eye. From the looks alone, it’s obvious that the Xonar D2 is an enthusiast part through and through.

Beyond cosmetics, the Xonar D2 is a 7.1-channel affair, based on the ASUS AV200 audio processor, which was ‘developed in cooperation with C-Media’, and boasts a stratospheric 118dB signal-to-noise ratio. If that wasn’t enough, ASUS states that the 118dB spec is valid for all seven output channels, in addition to the LFE channel. ASUS further tells us that this is different from some other generic audio card manufacturers, who only give the SNR for the two front channels, and use cheaper signal components for the other channels.

The ASUS Xonar D2 also boasts a wide range of DSP options, including Dolby Digital Live, Dolby Headphone, Dolby Virtual Speaker, and DTS Interactive, though as we’ve seen in the past, C-Media likes to take care of the DSP processing in software, which can mean extra CPU overhead when DSP options are enabled.

We’re excited to have one of the very first of these hotly anticipated audio products to come out of ASUS. If they’ve shown the same attention to detail with the Xonar products as they’ve shown with their enthusiast motherboards, we’re all in for a real audio treat. Could the ASUS Xonar D2 have what it takes to supplant the Razer Barracuda AC-1 as my reference sound card?

Packaging & Specifications

The retail packaging of the Xonar D2 is distinctly different from the design commonly seen on ASUS’ motherboard cartons. It features a stylish blue-and-white particle flow design, and features the contemporary Xonar logo design. Overall, it’s a very appealing box, which mimics the design of product boxes for software used in studio applications, and creates the impression of a ‘prosumer’ product.

The front of the box features a lift-up flap which reveals the Xonar card itself, which is protected by a PET shell. Also behind the flap is a listing of product features, accessories, and bundled software. When viewed from the bottom, the package allows a potential customer to see the full complement of gold-plated input ports the Xonar D2 offers (Bling, bling). ASUS has outdone itself on this packaging – this is superb product presentation.

The Xonar D2 product ships in a two-level PET shell, which both cradles the card itself and contains the bundled accessories. The bundle is very impressive – the Xonar package contains everything you need to connect the card to a multichannel A/V receiver for HTPC use. Four 3.5mm stereo miniplug to dual RCA connector cables are included, as well as an optical cable and four Toslink to mini optical converters. Also included is a slot cover with a 6-pin mini-DIN MIDI port, and a dongle which breaks the single MIDI connector out into two 5-pin MIDI connectors.

The Xonar D2 card itself features several styling cues that are meant to create the impression of a high-end audio component. The gold-plated connectors, gold-foil decals, and the large black metal shield contribute to that image. The card is also longer than both the Sound Blaster Audigy4 and the Razer Barracuda AC-1, about as long as most midrange video cards.

Xonar D2 Specifications

On the Xonar product box, ASUS provides a comprehensive list of the sound card’s specifications and capabilities, which are impressive to say the least.



ModelXonar D2/PM/AThe Xonar D2/PM package is the whole enchilada, so to speak. It includes an expansion slot cover with a MIDI I/O module
Audio CoreASUS AV200This chipset, which Asus tells us was ‘developed in cooperation with C-Media’, appears to be a re-branded CMI8788 OxygenHD codec chip, which is the same chip that we found on the Razer Barracuda AC-1.
Channels7.1ASUS states that their 118dB SNR applies to all channels of the Xonar D2 card, and that other cards typically only meet these specs on their front two channels.)
Digital Resolution24-bit24-bit audio is the same resolution that’s used by the DVD audio specification, so this card will have no trouble getting the most out of a 24-bit format digital recording.
Output Signal-To-Noise Ratio (SNR)118dBAThe SNR race rushes onward…This figure beats the recently-reviewed Razer Barracuda’s SNR by 1dB. But can you really hear this?
Input Signal-To-Noise Ratio (SNR)118dBANot many cards can boast input SNR figures equivalent with their output SNR. This holds some promise for ultra-high-quality recording.
Output Total Harmonic Distortion + Noise (THD+N)0.004% (-108dB)0.004% (-108dB)
Input Total Harmonic Distortion + Noise (THD+N)0.004% (-108dB)The fact that the Xonar D2 has the THD+N equal to its output stage makes this an even better option for use in a DAW. This feature also improves the functionality of an exclusive feature which ASUS calls ALT – an internal audio link between the output and input stages, enabling high-quality loopback recording without a loopback cable.
Output Frequency Response>10Hz to 90kHz (all channels)This expansive frequency response, which extends well beyond the range of human hearing at either end, ensures that distortion will be extremely low within the audible range (20Hz-20kHz), for the cleanest sound possible.
Input Frequency Response>10Hz to 46kHz (all channels)This recording frequency response allows extremely high quality recordings to be made, ensuring that even the very highest harmonics and deepest subharmonics can be detected and preserved on the recording.
Digital-to-Analog Conversion (Digital Sources)Burr-Brown PCM1796 x4 (123dB SBR, 24bit/192kHz Max)These four extremely high-quality stereo DACs by Burr-Brown (regarded as among the finest in the world) ensure that audiophile-quality digital-to-analog conversion will be available to all output channels of the Xonar D2. (The Razer Barracuda AC-1 card used slightly lesser-quality AKM DACs.)
Analog-to-Digital Conversion (Analog Inputs)Cirrus Logic CS5381 (120dB SNR, 24bit/192kHz Max)Even the card’s analog inputs get the high-end treatment with a high-quality Cirrus Logic ADC. The ADC’s high SNR ensures that a minimum of noise is added to the input signal, or during ALT recording.
Analog Playback Sample Rate & ResolutionUp to 192kHz @ 16/24 bit?This high maximum sample rate ensures that this card won’t add artifacts when playing digital material that samples at lower rates.
Analog Recording Sample Rate & ResolutionUp to 192kHz @ 16/24 bit`ASUS takes great pains to make it clear that the input signal path is capable of handling the resolution and quality of the output signal path, to lend credibility to the Xonar’s ALT recording feature.
I/O Full Scale Voltage2.0Vrms (5.65vpp)This card is capable of extreme voltage output, which is useful for driving inefficient earphones such as in-ears. Beware, however, that this level of output can cause hearing damage, and may overdrive the inputs of some devices.
S/PDIF Digital Output ModesUp to 192kHz @ 16/24-bit, Dolby Digital, DTS, WMA-ProThis card supports both Dolby Digital and DTS output, for receivers and preamp/processors that support the two formats. This is useful for HTPCs, but is standard fare for most sound cards. Not all receivers or pre/pros support input at the full 192kHz rate, however.
S/PDIF Digital InputUp to 192kHz @ 16/24-bit(This allows the card to accept digital inputs at full resolution, for bit-perfect recording.
ASIO 2.0 Driver SupportUp to 192kHz @ 16/24-bitASIO is a low-latency protocol for digital audio, which is most useful for studio applications, where equipment such as digital mixers require a low-latency connection with the sound card.
Analog I/O4x 3.5mm jacks (output), 2x 3.5mm jacks (input), 2x 4-pin headers (CD-In, Aux-In) on cardIt’s nice to have the ports directly on the sound card’s I/O panel, unlike the mildly inconvenient Razer HD-DAI connector on the Barracuda AC-1 which we reviewed earlier. Gold-plated connectors ensure positive signal transfer.
Digital I/OThese connectors serve as both optical jacks and RCA-style coaxial digital cable jacks. Optical connections provide the most positive signal transfer over long distances, however. Mini-Optical to Toslink converters (4) are supplied.These connectors serve as both optical jacks and RCA-style coaxial digital cable jacks. Optical connections provide the most positive signal transfer over long distances, however. Mini-Optical to Toslink converters (4) are supplied.
Digital I/OOther I/OMPU-401 compliant bracket with converterThe supplied dongle converts the mini-DIN connector on the bracket to the 180-degree DIN-5 connector used by MIDI devices.
Driver FeaturesDolby® Headphone, Virtual Speaker, Pro-Logic IIx, Digital Live; DTS® Connect, Interactive, Neo:PC; EAX® 1.0, 2.0; A3D® 1.0, DirectSound® Hardware Acceleration, supports DirectX 9.0 7.1-channel outputThe driver features list contains DSP algorithms developed by the biggest names in theater sound processing, such as DTS and Dolby Labs, as well as a variety of EAX®, Aureal3D®, and DirectSound® codecs. Support for EAX HD and EAX versions after 2.0 is absent, however, since Creative prefers to leverage their proprietary technology against the competition instead of sharing it.

Now that we’ve had our first impressions, let’s take a closer look at the componentry of the card itself.

Xonar D2 Hardware

ASUS is widely recognized as one of the premier manufacturers of PC hardware, so their decision to branch out into PC audio hardware alerts us to be on the lookout for an uncommon level of quality and attention to detail. It’s no wonder that the arrival of their Xonar products has created such a stir. A look at the Xonar D2 card itself makes it clear that ASUS isn’t simply looking to enter the market – they’ve launched a bid to dominate it. The Xonar D2 shares a skin-deep similarity to the recently-reviewed Razer Barracuda AC-1, therefore frequent comparisons between the two cards are more than merely incidental.

Warning: Intensely technical discussion follows. If you decide to simply skim the next section, we won’t be offended.

The most eye-catching feature of the ASUS Xonar D2 is the distinctively-styled steel shield that covers most of the card. The purpose of the shield is to protect the more sensitive audio components, specifically those that deal directly with analog signals, from electromagnetic interference (EMI).

Because the most barely-audible sonic details deal with extremely small voltage fluctuations at the signal level, any incident electromagnetic noise can seep in and make its way into the output signal. This is a particularly serious problem with many onboard audio solutions. The D2 has it covered, however (pun very much intended, thank you). The ‘ring’ in the center of the EMI shield illuminates when the Xonar card is powered up, emanating an appealing amber glow.

The removal of four tiny screws allows us to take a peek under the hood, so to speak. The card’s layout is similar to those we’ve seen in the past, but it’s not a C-Media reference design (see Sondigo Inferno). Much of the center of the card is blocked by the amber-colored plastic pieces that conduct light from LEDs to the large ring on the EMI shield. In the bottom center of the card is the ASUS AV200 (CMI8788 OxygenHD) codec chip, which is capable of stratospheric SNR ratings in excess of 118dB.

This is the same chip that Razer uses in their Barracuda AC-1 sound card, though its SNR specification stated a maximum of only 117dB. It is possible that C-Media has refined their manufacturing process to make their product capable of even higher SNRs. The CMI8788 chipset runs at 24.6 MHz, and is capable of 32-bit resolution (though the DACs used here only support 24-bit operation).

The ASUS Xonar cards feature extremely high quality Texas Instruments Burr-Brown DACs (Digital-to-Analog Converters). Burr-Brown DACs are featured in high-end audio equipment, from expensive multichannel receivers to high-end preamp/processor units, as well as in studio recording equipment. These particular DACs, the PCM1796, aren’t the top of Burr-Brown’s product line, but they’re a significant step up over the Asahi Kasei (AKM) DACs used in the Razer Barracuda card we reviewed in early April, with an additional 3dB of SNR. In addition, the Burr-Brown DACs introduce less than five ten-thousandths of a percent total harmonic distortion.

Why go so far? The DACs are only one component in the signal chain, but a signal chain may involve two or three stages of digital-to-analog conversion, or vice versa. Minimizing the amount of errant content (distortion, noise) introduced to the signal at every stage in the chain ensures that the cumulative effect will be inaudible, maximizing fidelity. Two of the DACs are visible here; the other two PCM1796 DACs are underneath one of the hemispherical amber-colored ‘wings’.

On the input side, the ASUS Xonar D2 card uses a Cirrus Logic CS5381 ADC chip to convert the incoming analog signals to a digital stream. The CS5381 is no slouch, offering the same quality as the AKM DACs used in the Razer Barracuda AC-1’s output stage with 120dB SNR and a THD+N spec that is 110dB down from the input signal. The CS5381 chip itself is hidden underneath one of the two illumination ‘wings’.

The ASUS Xonar D2 card’s output stage features Texas Instruments Burr-Brown OPA237 opamps, which are extremely high-quality units designed for applications where high slew rate is desired. While the Razer Barracuda sound card we reviewed earlier used four stereo (2-channel) opamps, these opamps are single-channel units. This ensures a large amount of physical separation and shielding between analog signal amplifiers, minimizing crosstalk and channel leakage. It’s encouraging to see that this more expensive route has been taken (stereo opamps would generate a meaningful net cost savings) in the interest of maximizing sound quality.

The Xonar D2’s circuit board is peppered with small, light-colored components labeled “NEC UC2-4”. These are miniature relays for switching the card to ALT recording mode. ALT stands for “Analog Loopback Transformation”, which allows the card to record directly from its analog output without using an external loopback cable. Because the Xonar can record at almost exactly the same quality level with which it plays back sound, ALT allows high quality recordings to be made from the card’s analog output. Asus advertises that this feature could be used to back up music files that are DRM-protected, allowing users to exercise their fair-use right to make a single archival copy of their digitally-stored, DRM-protected recordings.

With the Xonar’s high-quality signal path, there would be virtually no audible degradation to audio files produced in this way – the compression algorithms commonly used do far worse things to the waveform than the Xonar’s DAC–>ADC process. Of course, if you’re a stick-it-to-the-man type of person, this feature could potentially find other applications of questionable legality.

Other components found on the Xonar D2’s circuit board include JRC 5532 and 211C opamps, and a single National Semiconductor LM4562 opamp in one of the output stages, likely the LFE stage.

The Xonar D2 also features three internal 4-pin I/O connectors. The one furthest right is the MIDI I/O connector, while the other two are analog inputs for CD and Aux sources, respectively. The MIDI I/O module installs in an expansion slot, and connects to the Xonar D2 with an included 4-pin cable.

The I/O panel of the Xonar audio card features six gold-plated 3.5mm analog I/O jacks and two digital I/O jacks. However, one of the more novel features of the card is that each port is illuminated with a specific color, which makes it easy to find the right port even when the room is dark. What’s more, the lights also cast a nifty prismatic glow on the back wall. Unfortunately, if you would rather not have a PC that lights up like a Christmas tree, you’re stuck with the lighting, but it’s tasteful and hardly overdone.

Next, let’s look at the driver software for the ASUS Xonar D2.

Driver Software

The driver software for the ASUS Xonar D2 sound card reflects a significant effort on ASUS’ part to produce a professional-looking driver interface that is both usable and easy to understand.

The installation program for the Xonar D2 driver software is easy and intuitive to use, and features high-quality graphics that continue the particle flow theme from the product box. To install the sound card driver only, click on the upper button labeled “Audio Driver”. The lower button launches an install program that installs the additional included utilities, which include RightMark Audio Analyzer 5.6 and ASUS Portable Music Player (PMP).

The control program for the Xonar sound card is ASUS Audio Center. The Audio Center software is essentially an alternate embodiment of the reference control panel for the CMI8788 driver from C-Media, just as we saw with the Razer Barracuda AC-1 control panel. The initial display incorporates a rotary volume control knob and a VFD-style display that contains a spectrum analyzer and indicators for the active DSP modes. Four small buttons beneath the volume control allow you to quickly choose sets of DSP options that are most appropriate to gaming, music listening, or movie playback. The fourth button, labeled “Hi-Fi”, disables all DSP processing, for a pure signal path.

Clicking on the button labeled ‘Menu’ causes the VFD panel to slide upward, revealing additional controls. The first pane that appears is the ‘main’ panel, which contains options for adjusting the sample rate and the output mode (which affects the analog outputs). The output mode for the digital outputs can also be changed here, and Dolby Virtual Speaker may be activated (which simulates rear surround speakers from two or three front-stage main speakers) as well as an interesting DSP algorithm called ‘7.1 Virtual Speaker Shifter’ that allows you to modify the apparent placement the seven speakers in the room. This can be useful if your speakers aren’t placed in optimum locations.

The ‘Mixer’ pane mimics the functionality of the Windows Volume Control program, allowing you to adjust the level of each source independently. The changes you make to these controls will also appear in the Windows Volume Control. To view controls for recording inputs, simply click on ‘Record’. Here, you can access the ALT input feature. When you switch to the ALT input for recording, you’ll hear a small ‘click’ sound from inside your computer as the miniature relays redirect signals from the analog outputs straight to the analog recording inputs. If you switch away from ALT mode, you’ll hear another click.

The ‘Effect’ pane brings into view a 10-band graphic equalizer and settings for environmental DSP effects. The graphic equalizer has 12 presets, and allows you to create and store your own user-defined presets. The ‘Environment’ control group lets you simulate a variety of listening environments using C-Media’s Xear3D DSP algorithms. You can also tweak the apparent size of the listening environment.

While environmental DSPs of the past were cheesy and only served to destroy fidelity, the ASUS AV200’s environmental DSPs are actually realistic, and deliver substantially better sound quality. Still, I prefer to do my listening without any additional effects. The ‘Karaoke’ pane displays even more DSP options, related to pitch shifting and vocal removal. Pitch shifting can even be applied exclusively to the microphone input. The vocal removal option, however, adds substantial dynamic compression to the card’s output. I typically regard these DSP options as novelties, as only the most adventurous enthusiasts will care to experiment with them.

The last pane of DSP options is the ‘FlexBass’ pane, which offers a wealth of options for tweaking the LFE output of the card. These options closely emulate those of a high-end preamp/processor, allowing you to not only set an upper LF cutoff frequency for the subwoofer, but selectively exclude that frequency range from the main speakers as well. The LFE Crossover Frequency slider allows you to select a crossover frequency anywhere between 50 Hz and 250 Hz. This range of adjustment gives you the flexibility to set an appropriate crossover frequency for just about any size subwoofer or main speakers, though the THX-specified LFE crossover frequency is 80 Hz.

Setting the “L|R” control to “Large” causes the card to pass deep bass to the main speakers as well, while setting the control to “Small” excludes frequency content below the crossover frequency from the main speakers, an option that’s useful for small satellite speakers.

Clicking on the small arrow tab to the right of the volume control causes a small panel to slide out with quick-access buttons for the bundled software applications. Next, we’ll take a look at the programs ASUS bundles with the Xonar retail package.

Bundled Software

The ASUS Xonar D2 is an impressive part, with eye-catching aesthetics, audiophile-quality components, and a great hardware bundle. However, ASUS didn’t stop there – they’ve also thrown in a fantastic deal-sweetening software bundle, with titles from names like Cakewalk and Ableton.

Ableton Live Lite Xonar Edition

Ableton Live is a music production tool that handles all stages of the production process, from recording to multitrack sequencing and arranging. The Live Lite Xonar edition has some of its features disabled, and can only record 64 simultaneous tracks, but retains most of the functionality necessary to produce high-quality multichannel recordings. Live Lite is also limited to two audio input channels and four audio output channels, as well as only two audio effects per track. While this obviously won’t let you fully kit out a small recording studio, it’s plenty useful for homemade recordings, and gives a taste of what’s possible with modern DAWs.

Cakewalk Sonar LE

The ASUS Xonar software bundle also includes the Production Plus Pack from Cakewalk, which includes Sonar LE, Dimension LE, and Project5 LE. Sonar LE from Cakewalk is another DAW program which allows you to produce high-quality multitrack recordings. Sonar LE is a limited version of Cakewalk’s Sonar 6 Studio, but provides the familiar Cakewalk Sonar interface. Sonar LE allows simultaneous multitrack recording, MIDI recording, and even virtual instruments. Sonar LE is also compatible with both 32-bit and 64-bit operating systems. From what I’ve seen, it’s likely that you’ll get more use from Sonar LE than you will from the bundled version of Ableton Live Lite.

Cakewalk Dimension LE

Cakewalk Dimension LE is a program that creates custom sounds for MIDI instruments. It doesn’t have an ‘application’ per se – rather, it shows up within Ableton Live or Cakewalk Sonar, and allows you to make modifications to its settings. In that respect, its functionality is more similar to a plug-in. Dimension LE lets you tweak every aspect of your instrument’s sound, and even composite up to four different instrument sounds together.

Cakewalk Project5 LE

Cakewalk’s Project5 LE software provides a simplified interface for multitrack recording, MIDI sequencing, arranging, and editing. Project5 LE also supports the Dimension LE interface for customizing the sound of digital instruments. The purpose of Project5 is to provide an easy-to-use interface for Cakewalk’s powerful software features, in order to let less-experienced musicians take advantage of its power, while experienced studio gurus may prefer Sonar LE’s interface.

CyberLink PowerDVD 7

ASUS also bundles Cyberlink’s PowerDVD software with the Xonar card, to provide high-quality DVD playback using the software decoder. This is especially useful if your video card’s drivers don’t include a DVD decoder.

Other bundled items include version 5.6 of Rightmark’s Audio Analyzer software, and a DVD- Video disc from Dolby Labs showcasing their Dolby Headphone and Dolby Virtual Speaker DSP technology. Now that we’ve looked at everything the ASUS Xonar D2 product has to offer, let’s move on to some testing and measurements.


While some sound cards may differ more substantially in audible ways from other sound cards, the only way to truly quantify the most subtle differences between high-quality sound cards is to measure and analyze their output. While in a laboratory setting, expensive lab-grade testing equipment may be used, in our experience a far simpler and almost as telling measurement method is the ‘loopback’ test. In loopback testing, the output of the sound card is routed through its ‘line in’ input, and recorded simultaneously with the test signal playback.

A minor disclaimer: The resulting measurements from loopback testing may be affected by other factors, such as the quality of the input ADC circuitry, since the entire input/output signal chain of the card is tested. However, this limitation only limits our ability to provide absolute measured values – the results from loopback testing are still plenty useful for comparing sound cards to each other. The measured values you see here may not be the numbers that the sound card is capable of under ideal conditions as measured by high-dollar testing equipment, so don’t be alarmed if the numbers we give here aren’t the same as the numbers that appear on the box.

For comparison testing, we’re using two other sound cards that we’ve got on hand, the popular 24-bit/192kHz-capable Creative Sound Blaster Audigy4 (113dB SNR) and the recently reviewed Razer Barracuda AC-1, formerly my personal reference sound card. The Razer Barracuda AC-1 is also based on the C-Media CMI8788 OxygenHD chipset and rated for the stratospheric SNR of 117dB. However, the Xonar D2 card uses higher-quality DACs and analog signal components than the Barracuda AC-1. This selection of cards makes for quite an interesting match-up, indeed.

RightMark Audio Analyzer 6.0.5

For the audio measurements, we’re using the latest version of RightMark Audio Analyzer, version 6.0.5 (newer than the 5.6 version included with the Xonar D2 bundle). Despite its quirks, RightMark Audio Analyzer is the only game in town when it comes to powerful benchmarking functionality for sound cards. The full battery of tests was performed on all three sound cards, in three audio modes: 16-bit/44.1kHz, 24-bit/96kHz, and 24-bit/192kHz. However, in some cases, the swept-frequency THD+N and IMD+N tests produced some strange results, no matter what we tried. For your identification, we’ve flagged the suspect measurements in red.

RMAA, 16-bit/44.1kHz Mode

Measurement Type


Barracuda AC-1

Xonar D2


Frequency Response (Multitone)+0.10/-0.26+0.03/-0.11+0.07/-0.04(dBa)
Frequency Response (Sweep)+0.1/-0.2+0.0/-0.0+0.0/-0.0(dBa)
Signal-to-Noise Ratio90.895.896.8(dBa SNR)
Dynamic Range90.895.896.2(dBa)
Total Harmonic Distortion (THD)0.0047%0.0039%0.0008%Less than
Total Harmonic Distortion (THD, Swept Freq)-76.21/-82.77-75.00/-87.91-88.01/-89.61(dB, unity-referenced)
Intermodulation Distortion (IMD+N)0.0093%0.0075%0.0046%Less than
Intermodulation Distortion (IMD+N, Swept Freq.)3.698%0.037%0.389%Less Than
Stereo Crosstalk-84.1-95.8-96.5(dB, unity-referenced)

RMAA, 24-bit/96kHz Mode

Measurement Type


Barracuda AC-1

Xonar D2


Frequency Response (Multitone)+0.01/-0.09+0.02/-0.10+0.07/-0.04(dBa)
Frequency Response (Sweep)+0.0/-0.0+0.0/-0.0+0.0/-0.0(dBa)
Signal-to-Noise Ratio89.6106.3115.9(dBa SNR)
Dynamic Range89.8105.8115.8(dBa)
Total Harmonic Distortion (THD)0.0059%0.006%0.0006%Less than
Total Harmonic Distortion (THD, Swept Freq)-72.29/-75.87-72.39/-92.83-78.57/97.27(dB, unity-referenced)
Intermodulation Distortion (IMD+N)0.011%0.008%0.0017%Less than
Intermodulation Distortion (IMD+N, Swept Freq.)0.014%0.035%0.0006%Less Than
Stereo Crosstalk-77.5-99.8-102.2(dB, unity-referenced)

RMAA, 24-bit/192kHz Mode

Measurement Type

Barracuda AC-1

Xonar D2


Frequency Response (Multitone)+0.02/-0.10+0.06/-0.04(dBa)
Frequency Response (Sweep)+0.0/-0.0+0.1/-0.0(dBa)
Signal-to-Noise Ratio106.0115.9(dBa SNR)
Dynamic Range105.6115.8(dBa)
Total Harmonic Distortion (THD)0.0063%0.0006%Less than
Total Harmonic Distortion (THD, Swept Freq)+16.15/-77.65-59.28/-81.77(dB, unity-referenced)
Intermodulation Distortion (IMD+N)0.0083%0.0019%Less than
Intermodulation Distortion (IMD+N, Swept Freq.)0.035%0.0006%Less Than
Stereo Crosstalk-100.3-102.3(dB, unity-referenced)

ALT Test, RMAA, 24-bit/192kHz Mode

Measurement Type

Barracuda AC-1

Xonar D2


Frequency Response (Multitone)+0.06/-0.04+0.06/-0.04(dBa)
Frequency Response (Sweep)+0.1/-0.0+0.1/-0.0(dBa)
Signal-to-Noise Ratio115.8116.5(dBa SNR)
Dynamic Range115.6116.4(dBa)
Total Harmonic Distortion (THD)0.0007%0.0006%Less than
Total Harmonic Distortion (THD, Swept Freq)-59.29/-81.78+16.24/-81.77(dB, unity-referenced)
Intermodulation Distortion (IMD+N)0.0018%0.0017%Less than
Intermodulation Distortion (IMD+N, Swept Freq.)0.0007%0.0007%Less Than
Stereo Crosstalk-102.9-112.5(dB, unity-referenced)

Frequency Response
Throughout testing, the ASUS Xonar D2 delivered a smoother frequency response with less overall variance than either of the other two cards. The maximum variance range displayed by the Xonar D2 card was 0.11dB, however at a 192kHz sample rate, the range was only 0.1dB. The Razer Barracuda came in second place here, with a variance of 0.14dB. The Audigy4 card holds its own here, but still comes up last with a maximum variance range of 0.36dB observed at the 44100Hz sample rate. For all three cards involved, these are very ‘flat’ frequency response numbers.

Signal-to-Noise Ratio (SNR)
The greatest signal-to-noise ratio in each of the three tests consistently belonged to the Xonar D2, especially at 24-bit resolutions. The minimum SNR observed for the Xonar card was 96.8dB, though the maximum SNR topped out at 115.9dB. The Razer Barracuda AC-1 came in second place again, maxing out at 106dB SNR in loopback testing. Keep in mind, however, that this testing method tests the entire signal path, including the quality of the input analog-to-digital conversion. Last of all was the Audigy4 card which delivered a top SNR of 90.8dB, a figure that’s possibly also hamstrung by its input stage.

So, what’s the significance of SNR? Lately, it seems to be the specification that gains the most traction in marketing a card. Signal-to-noise ratio describes a ratio of the decibel level of a unity-gain signal over the ‘noise floor’, beneath which audible signals seem to disappear in a mess of hiss and noise. A high SNR is responsible for the relative ‘blackness’ of musical silences. ASUS’ Xonar card claims a high 118dB output signal-to-noise ratio, while its output DACs are capable of a 123dB SNR. Therefore, the limiting factor here may be the AV200 audio chipset itself (CMI8788).

Dynamic Range
This parameter refers to the relative decibel level between the quietest sound the card can reproduce and the loudest sound it can reproduce. Typically, this tends to coincide with the overall SNR of the card, which means that the quietest sound that RMAA could detect was a sound that was just above the noise floor of the card. Naturally, the ASUS Xonar D2 was found to exhibit the greatest dynamic range of the three cards.

Total Harmonic Distortion (THD)
Of the three cards compared in testing, the ASUS Xonar card delivered the lowest level of total harmonic distortion (a mere six ten-thousandths of a percent). For measurement purposes, THD levels below the noise floor cannot be accurately measured, so the two values are commonly composited into another parameter, THD+N.The Razer Barracuda AC-1 again came in second in this test, with a minimum THD of 0.0036% at the 44100kHz sampling rate. The minimum THD value for the Audigy4 card was 0.0059%.

Perhaps even more than SNR, Total Harmonic Distortion is an important parameter for describing the overall ‘musicality’ of the sound card, because it describes the sound card’s ability to deliver a pure tone without added harmonic content. A high THD figure would manifest itself as a sort of ‘hash’, much like the distortion of an electric guitar. Lower total harmonic distortion means that the card’s output is more ‘pure’ and uncolored by distortion products.

Intermodulation Distortion (IMD)
Intermodulation distortion occurs when two waveforms sum constructively and destructively, resulting in an additional third distortion product that contains frequencies that are in neither of the two original signals. Intermodulation distortion also can have a destructive effect on overall clarity. The lowest ‘intermod’ distortion once again was turned in by the Xonar D2 card. In a reversal, the Xonar’s low IMD figure was followed closely by the Audigy4 card, with less than 0.014% IMD+N. Bringing up the rear was the Razer Barracuda card, with a minimum of 0.035% IMD+N.

Stereo Crosstalk
This parameter describes how much of one stereo channel ‘leaks’ into the other stereo channel throughout the signal chain on the sound card. This parameter is given as the overall level of the signal that has leaked into the other channel. These are all multichannel sound cards, but typically the front left and right signals are routed together through the card. One potential way of reducing crosstalk through a stereo signal is to route stereo pairs of signals through separate DACs and preamplifier circuits, but this is a board design thing, and not something we can adjust.

ALT Recording
This test measured the overall benefit of the ALT recording feature of the Xonar D2 card with respect to the traditional loopback cable method, using a short loopback cable. Of particular interest here are the SNR and crosstalk ratings. The use of ALT mode resulted in 0.7dB greater SNR, a small improvement. However, stereo crosstalk in ALT mode was nearly 10dB lower than it was inside the loopback cable. This means that ALT is not only a more convenient solution than a loopback cable – it’s a better-sounding solution as well for preserving your recordings in the most pristine form possible.

Performance Testing

As we’ve seen in the past, sound cards and positional audio processing can be responsible for a significant amount of CPU overhead in 3D gaming. Different audio codec chips handle different amounts of the overall DSP processing, and the rest is offloaded to the CPU. When we reviewed the Razer Barracuda sound card in April (based on the same basic CMI8788 chip design as the ASUS Xonar), we found that the CMI8788-based chip relied heavily on the CPU, creating substantially more processor overhead.

RightMark 3DSound 2.3 CPU Utilization Test

To make these measurements, RightMark 3DSound 2.3 was used to generate random noise and load each audio card with a number of concurrent buffers, which was varied to show a trend in the increase of CPU usage based on different cards. Test sets were performed for 16, 32, 63, and 127 buffers, respectively. The program’s algorithm monitored CPU usage over a period of 1 minute for each test, and then averaged the values over time. All other programs running on the computer were closed to minimize variance caused by other programs vying for the CPU.

Here’s what the results show: Through all testing, the Creative Sound Blaster Audigy4 card delivered the lowest overall level of CPU utilization, staying under 10% even in the demanding 127-buffer test. The number of buffers increased at approximately n^2 for every scale division, while the CPU usage for the SB Audigy4 remained fairly constant. The Razer Barracuda AC-1 turned in the worst performance here, despite its styling as a ‘gaming’ audio card.

It appears that the newer CMI8788 drivers supplied with the ASUS Xonar D2 have managed to reduce CPU overhead somewhat, but in the 127-buffer test, CPU usage just barely tickled the 30% mark. The 127-buffer test is an extreme case, but it shows that the ASUS Xonar may not be the best card for gaming, a point only further reinforced by the lack of support for EAX versions after 2.0.

Next stop: Listening tests.

Listening Tests

Despite the obvious value of measurements and synthetic benchmarks in determining the merits of a piece of audio hardware, eventually it all comes down to the way in which the upgraded audio solution can benefit your listening experience. With that in mind, you’ll be glad to know that we fully tested the ASUS Xonar D2 with a variety of listening material…for hours on end.

Switchfoot Nothing Is Sound DVD-Audio

The Xonar D2 card surprised me with the amount of depth and detail that it was able to retrieve from this high-energy rock recording. Listening through a fairly ordinary $150 set of 2.1 speakers from Cambridge Soundworks, I heard details I had never heard before – even with headphones – when played on my PC.

The Xonar card wowed me with its spectacular transparency and panoramic imaging. The digital effects came through clearer and cleaner than ever before. Even formerly ear-fatiguing distortion guitar sounds sounded clear and smooth, and percussion instruments were rendered dynamically, with a tight, gut-punching kick drum and clear, crisp cymbals. Every instrument seems to inhabit its own acoustic space, thanks to the vanishingly low distortion of the Xonar.

Bela Fleck and The Flecktones UFO Tofu Audio CD

On UFO Tofu, the superb sound quality of the Xonar D2 allowed me to enjoy this record in a way I never have before on my PC. Track 2, “Sex in a Pan,” showcases the funk bass stylings of Victor Wooten front and center, and once again the fantastic dynamic range of the Xonar D2 card shined through, rendering every slap and pluck with percussive impact and full-bodied tone. Track 3, “Nemo’s Dream,” the clarity was astonishing – every instrument again seemed to fill its own acoustic space within the recording, instead of seeming to blend together. Imaging was also superb, with stereo pickups on the electric bass and banjo creating a sonic experience that must be heard to be believed. Even during loud passages, Bela Fleck’s plucking of the individual banjo strings could still be heard.

Compared to the other two audio solutions we tested for this review, the ASUS Xonar D2 sound card is a revelation – its high quality analog signal chain and vanishingly low distortion results in an eminently musical piece of hardware. It just sounds so…right. Overall clarity is superb, and you’ll hear details you never noticed before, especially if you own an expensive, good-sounding set of speakers or high-quality headphones.

However, perhaps the greatest compliment to the Xonar’s stellar sonic fidelity is its ability to make even my humble $150 Cambridge Soundworks 2.1-channel set sound fantastic – I felt no need to switch to headphones. When I did, however, what I heard there simply confirmed what I had been hearing through my speakers – incredible definition and detail that I didn’t even hear from my previous reference sound card, the Razer Barracuda AC-1.

Final Thoughts

The ASUS Xonar D2 impressed us at just about every turn. Through and through, a high-end approach has been taken to the design of the Xonar, from extremely high quality circuit components to rock-solid driver software. However, the secret weapon of the Xonar sound card is its extremely low distortion.

With all the marketing play that is given to signal-to-noise ratio specifications, distortion figures go mostly unnoticed. However, with harmonic distortion figures that match the top-of-the-line Creative X-Fi Elite Pro, the Xonar cards are capable of breathtaking musicality, and this is evident in listening tests with high quality sources. In short, we were wowed by the audio performance of the Xonar D2.

The Xonar D2 card may not be so perfect for everyone, however. In our RightMark testing, the Xonar card still placed a relatively large amount of overhead on the CPU for DSP processing when dealing with a large number of simultaneous buffers – significantly more than the old Audigy4 card we used in our comparison testing. The Xonar sound card also lacks support for EAX versions above 3.0, which means that gaming audio performance suffers somewhat.

Of course, EAX is proprietary Creative Labs technology, so the very fact that we have to grade down the Xonar D2 because of its lacking EAX support goes to show just how tied-up the gaming industry is with Creative’s proprietary positional audio technology. Neither of these shortcomings limit the Xonar’s appeal for music listening, home studio use, or high-fidelity music listening, however, which appears to be where the Xonar D2 is targeted.

From the outset, it looked like ASUS was preparing the Xonar products to be X-Fi killers in terms of sound quality, but what they’ve really succeeded in doing is delivering a product that’s an excellent value. It delivers the extremely high SNR and low distortion of Creative’s X-Fi Elite Pro sound card, at a price that’s about $70 less. For that $70, though, you give up the X-Fi Elite Pro’s breakout box and hardware DSP acceleration. What you get instead is one very sexy-looking piece of audio hardware, and a fantastic suite of bundled software. We’re pleased to award the ASUS Xonar D2 a well-earned Techgage score of 9/10, and I’m proud to make it my Editor’s Choice product for September.

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