Universal Soldier: ASUS Xonar D2 PM Sound Card Review

These days, when every mainboard comes with an integrated sound adapter, few manufacturers dare release discrete audio solutions. Many brands have left the market altogether, others have halted the development process and don’t care much about driver updates. That’s why every new device provokes a huge interest in the PC audio community. We are going to talk about a device like that – a sound card from ASUS.

by Sergey Romanov
05/14/2008 | 04:28 PM

These days, when every mainboard comes with an integrated sound adapter, few manufacturers dare release discrete audio solutions. Many brands have left the market altogether, others have halted the development process and don’t care much about driver updates. That’s why every new device provokes a huge interest in the PC audio community. And when a new brand comes to market, it is a real sensation. A standalone sound card is supposed to be far superior to the integrated sound of mainboards. Otherwise, it makes no sense at all. Considering Creative’s monopoly on gaming technologies, the single argument in favor of a standalone sound card may be its quality of music playback. More exactly, it is the price-to-quality ratio because expensive components and a meticulously designed PCB make the end product too expensive whereas cheap components don’t yield the desired quality. The price also includes the cost of developing and updating the driver. Having weighed all the pros and cons, most manufactures preferred to avoid such an inconvenient product as a non-professional sound card, yet the niche doesn’t remain empty. The young and daring company Auzentech announced its arrival by releasing a few interesting products based on C-Media’s controllers. The X-Fi Prelude 7.1 brought an international success to the company. In 2007 another serious player stepped on the scene: the world-famous hardware manufacturer ASUS began to sell a pretentious audio solution for PCI and PCI Express buses.


As a matter of fact, ASUS is not really a newcomer in this market. Last century the company produced a PCI sound card called ASUS 3DexPlorer AXP-201. And some time previously, there was an audio-video combine for a special PCI/ISA slot installed on some of ASUS’ mainboards, e. g. ASUS T2P4. It was about ten years ago, and now the company makes a second attempt to establish its brand on the sound card market. Drawing on its earlier experience, ASUS puts its stake on wide functionality coupled with highest technical characteristics. The company chose a good strategic partner to quickly and cleverly solve the task. For the Taiwan-based C-Media Electronics the partnership with ASUS is surely an opportunity for further growth, so this collaboration is mutually beneficial.

January 2006, at a Las Vegas expo, C-Media introduced a number of interesting solutions, two of which pertain to the subject of this review: the PCI audio controller C-Media Oxygen HD, which equaled the widespread VIA Envy 24HT in its capabilities, and the digital sound processing software C-Media Hydrogen that provided support for DirectSound3D, licensed technologies from Dolby Laboratories, and a number of other features I’ll describe when I’ll be talking about the ASUS sound card.

The mixture of Oxygen and Hydrogen gave birth to a lot of sound cards from then-obscure firms such as Bluegears, Sondigo, HT Omega, Auzentech, and Razer. ASUS just couldn’t stay aside.

Let’s view the specs of the C-Media Oxygen HD in comparison with the VIA Envy 24HT.



Oxygen HD

PCI interface

PCI 2.2 with bus mastering and burst modes

Sample rate

up to 192 kHz


24 bit

32 bit

Outgoing streams



Ingoing streams



I2S output pairs



I2S input pairs



S/PDIF transmitter


S/PDIF receiver




Both chips support programmable reassignment of the output channels and digital monitoring of the inputs. One of the five dual-channel I2S outputs of the Envy 24HT is assigned to the digital output equipped with an integrated transmitter, but allows connecting an additional device with an I2S interface. The Oxygen HD lacks this capability but features an integrated S/PDIF receiver whose signal can be sent directly to the digital output, which allows using the sound card as an adapter from the optical to coaxial cable and vice versa. The Envy 24HT can only record simultaneously from two stereo sources (usually, from the ADC and S/PDIF) whereas the Oxygen HD allows recoding from three sources at once (one is an eight-channel source). The sources can be flexibly selected from among the four input I2S pairs, integrated digital input and even two AC’97 codecs.

C-Media Oxygen HD Flowchart

Judging by the description, the chip is free from obvious weaknesses and can make a good foundation even for a professional sound card. But today I’m going to discuss a product intended for home use in a multimedia center or in a gaming PC.

Package, Accessories and Design

The accessories are gorgeous. Besides an installation manual, the box contains four analog cables 1.8m long (mini-jack → 2xRCA), a thin one and a half meter long optical cable, a bracket with a MIDI port, and a lot of CDs: installation disc, applications, demo disc from Dolby Laboratories.

The card itself differs from regular sound cards with its anodized-aluminum armor which endows it with a very imposing, serious appearance. The round cutout in the armor makes it look like a graphics rather than sound card.

The mounting bracket is ordinary enough, though. It’s the same as with the Auzen X-Fi Prelude 7.1: six 3.5mm connectors (microphone input, line input, four stereo outputs) and two RCA connectors (digital input and a digital output).

Another similarity to the Auzentech product is that the digital connectors support both coaxial and optical cables via special adapters you can plug into them.

ASUS’ engineers found a way to make their product different, though. There are multicolored LEDs inside each of the six mini-jacks. This resembles, though remotely, the color coding of connections according to the PC 99 instructions (page 60).

Besides just being pretty, this elegant solution makes it easier to connect the cables to the sound card. You can tell you hit the necessary connector if the appropriate light doesn’t shine behind your PC. By the way, the included cables have a small diameter of the plastic part of the connector for easy connection of a multi-channel speaker set to the card.

The PCB carries CD IN, AUX IN and MIDI I/O headers. You can attach low-quality sources such as a TV-tuner to the former two. Their signal goes to the recording mixer but it can also be sent to the sound card’s outputs by pressing the appropriate Monitoring button in the Xonar Audio Center. The bracket with a mini-DIN port is connected to the MIDI I/O header. Large DIN connectors (MIDI In and MIDI Out) are provided by a special Y-shaped adapter.

Layout and Internal Configuration

The product description gives some information about the hardware components covered by the protective armor:

The rest can be seen if the casing is removed: original squares of film capacitors (I have not seen them before in any mass-produced sound card) in DAC filters, solid-state electrolytic capacitors, a handful of electromagnetic relays (more than on the Creative X-Fi Elite Pro), four voltage regulators at the right edge of the PCB, and a huge number of operation amplifiers.

The DACs employed on the card, like most top-class chips of this type, have balanced current outputs. It means the signal must be converted into voltage before the low-pass filter, which triples the amount of necessary opamps.

Cheap dual-channel 4580 amplifiers from Texas Instruments are used on three out of the four output channels. The front output uses more expensive NJM2114 (at the I/U conversion step) and LM4562 (in the low-pass filter) amplifiers. Besides, two RC4580 are installed on the front output as a buffer for connecting the headphones directly to the sound card. This solution was used before for the headset output on the M-Audio Revolution 5.1 and Audiotrak Prodigy HD2 cards.

The ADC filters are based on the NJM5532 but the RC4580 is used as the inverter for the DAC’s balanced inputs. These various opamps indicate the developer’s effort to optimize the product’s price/quality ratio. Let’s see what is different between these chips.

The four models are all recommended by their manufacturers for the use in sound devices, and three of them have similar specs. All the chips feature good tolerance to variations in the supply voltages and the ground as well as a low level of harmonics in the audio range. The LM4562 differs from this group with its response and distortions, provoking some questions to the developer.

You can learn about the advantages of the LM4562 over other opamps (including the NJM2114) by the example of the Creative X-Fi Elite Pro in our previous review. I/U-conversion opamps are used in inverting circuits, and the LM4562 would work well in this cascade, too. The combination of it with the NJM2114 looks strange as it has a narrower pass band and introduces more distortions. Moreover, the RC4580-based output buffer is good for headphones but nearly negates all the advantages of the LM4562 when working with a high-resistance load. Added to that, the film capacitors in the filters’ feedback circuit work together with ceramic capacitors in the feedback circuit of the I/U conversion cascade. So, the subunits of the card’s analog section seem to have been developed by different engineers who didn’t collaborate.

Now I’ll tell you about the converters installed on the Xonar D2. The Burr-Brown PCM1796 belongs to the Advanced Segment DAC class and is claimed to combine an excellent dynamic range with low sensitivity to jitter. The converter has a dynamic range of 123dB and a THD+noise of 0.0005% for sample rates of 44.4, 48 and 96kHz under normal conditions. The latter parameter increases at 192kHz.

The graphs below are built for the typical application circuit of the DAC. The I/U conversion and filtering cascades of the typical circuit employ NE5534 opamps, which are not exceptional in terms of distortions, so other implementations may bring even better results.

However, Texas Instruments produces an even better model, PCM1792A, which ensures a dynamic range of 127dB and a THD+noise below 0.0004% for sample rates of 44 and 48kHz.

Interestingly, this model is pin-compatible with the PCM1796 and has the same command set. It could be used on the Xonar D2 without any modifications of the PCB if it didn’t cost four times as much as the PCM1796. Frankly speaking, I don’t think it’s reasonable for the sound card’s four outputs to be identical quality. ASUS engineers seem to agree with me, using cheap opamps on every output save for the front one. Following the reasonable sufficiency principle, the rear channels could be based on the PCM1791A (a dynamic range of 113dB, 0.001% TDH+N) that is not only 30% cheaper than the PCM1796 but also doesn’t need an I/U conversion cascade, which would allow to do without six opamps and a number of support elements. There is an even more radical variant of redesign that would yield a low-profile version of the card: the six-channel PCM1602A (a dynamic range of 105dB, 0.002% THD+N) provides three stereo outputs at a lower price than the PCM1796’s one. By the way, the recently released low-profile Xonar DX card is designed in a similar manner: a high-quality dual-channel DAC (Cirrus Logic CS4398, like on the Creative X-Fi Elite Pro) for the front output and a six-channel Cirrus Logic CS4362A (114dB dynamic range, 0.001% THD+N) for the remaining three outputs.

The Xonar D2’s analog-to-digital converter is based on the best model from Cirrus Logic, CS5381, which ensures a SNR of -120dB and a THD+N of 0.0003% at all sample rates up to 192kHz.

This may be the highest-quality mass-produced analog-to-digital converter. Theoretically, it can be used for very precise signal measurements at frequencies up to 50kHz (above that point the signal is suppressed by the digital filter even at a sample rate of 192kHz) but the analog section must be top-class as well. The ADC developer recommends to base the filter on low-noise opamps LT1128 from Linear Technology which have a minimized offset voltage and a superb level of distortions (about -130dB), but ASUS employed NJM5532 opamps which are not so high quality.

Driver Functionality

The Xonar D2 driver differs from the basic C-Media Oxygen HD driver because it supports OpenAL, SVN and DS3D GX. It also has a different interface stylized like a pocket media player. Upon installation, the control panel shows a minimum of controls, a volume control, and a large information display with current settings and a primitive spectrum analyzer.

It is primitive because it is not accurate (to reduce the CPU load). The round volume control looks good but is not very handy. It is rather difficult to turn it with your mouse, and it doesn’t react to your mouse wheel at all.

Pressing on the “i” button you can view the versions of software components and some other information.

The SVN button near the volume control enables the volume normalization mode which may come in handy when you are watching a movie with quiet voices but loud special effects. This feature is not good for games as it makes shots and explosions sound fuzzy, worsening your aural impressions.

The group of five buttons in the bottom right corner of the audio center window enables the DS3D GX feature and one of three sound processing presets: games, movies, music. The HF option, on the contrary, disables all processing; it’s in this mode that I performed all the tests. The rest of the controls are hidden under the removable cover of the information display.

Here you can choose the card’s base frequency, specify the number of speakers, choose the data format for the digital output, and change the settings of the licensed technologies from Dolby that are enabled by the above-mentioned presets. For example, each of them enables Dolby Headphone for headphones. For stereo speakers, there are Dolby Pro Logic IIx and Dolby Virtual Speaker.

A number of other setup options open up on your pressing appropriate buttons. Why did they have to hide all this abundance under the control panel’s very slow cover? Fortunately, you only have to wait once for the cover to move. The selected position is saved in the registry thereafter.

As you see, the available selection of settings depends on the configuration of the speaker system. For some reason, the DPL IIx and DTS settings are missing for two speakers, and Pro Logic is turned on automatically on enabling Dolby Virtual Speaker. For headphones, Virtual Speaker Shifter is enabled only when Dolby Headphone is turned on.

In C-Media’s basic driver the Virtual Speaker Shifter option is independent from Dolby Headphone to enable technologies for converting stereo into multi-channel sound. Thus, Virtual Speaker Shifter seems to create a virtual 7.1 system and then mix the sound into the necessary number of channels. There is nothing like that in the latest driver, and it may be just a trivial error in the driver or its control panel.

The position of a speaker in the virtual room determines the volume of the appropriate playback channel. If you transfer, for example, the right speaker to the left, both channels will be mixed into the left “ear”. This setting can be viewed as a simplified alternative to Creative’s THX Console but with lower functionality. In THX Console you can specify the distance (in meters) and direction (in degrees) for each speaker system component, and the volume and signal delay for the appropriate channel are adjusted accordingly. ASUS’ implementation is not linked to any measurement units. The user is supposed to select the position of the speakers “by ear”. Why is there no test signal then I wonder?

For comparison, C-Media’s basic driver shows the relative volume in decibel and allows you to specify the delay for the central and rear channels. It also offers three test signals to evaluate the result. By the way, if you install ASUS’ driver manually rather than through Setup.exe, you can see the original control panel from C-Media.

ASUS’ digital output settings differ from those of the basic driver, too. This time the difference is for the better. You can select the output format and frequency for the whole card (including its DAC/ADC) – it remains in effect even when the digital output is disabled. C-Media’s control panel only allows selecting the base frequency when the S/PDIF interface is on.

The Xonar D2’s S/PDIF interface can transmit uncompressed stereo (with a sample rate of 44.1 to 192kHz) and 5.1 sound in Dolby Digital Live or DTS Interactive formats. It can also transfer the unprocessed signal from the digital input. The latter option allows using the card as an adapter from a coaxial into optical cable and vice versa. When DDL or DTS encoding is enabled, the card enters 5.1 mode, disabling the analog outputs. The volume control continues to work then, and you can enable the automatic SVN adjustment.

Dolby Pro Logic IIx is responsible for splitting stereo into 5 speakers although this technology can do the opposite thing for headphones or a dual-speaker system, i.e. it can downmix multi-channel sound into stereo. DPL IIx supports 7-speaker systems and has three operation modes but the ASUS Xonar offers only Music and Movie modes, the Game mode being missing. In the Music mode you can set up the sound field depth and the balance of medium frequencies (vocals) between the central and two front speakers. The Panorama option, available in the original control panel from C-Media, has been lost somehow, too.

Stereo can be split into multiple channels by means of the alternative technology DTS Neo:PC that has the same settings of the operation modes.

Well, we’ve given enough our attention to one settings group. Let’s proceed further.

Next goes the Mixer section.

Like with many other sound cards, the reproduction mixer is independent from the recording mixer, which makes you press an extra button when you need to adjust your recording settings. The original control panel from C-Media contains the reproduction and recording settings on the same page, which is handier. The problem is the Xonar D2 Audio Center has no level indicator (the so-called peak-meter) although C-Media’s panel has two such indicators. A good example is the control panel of the Audiotrak Prodigy 7.1 where each volume regulator is accompanied with a signal level indicator.

Besides the traditional volume regulators for Wave, MIDI and CD, you can independently adjust the volume of each of the card’s analog outputs. Take note they are not set at their maximum volume by default.

In the recording mixer you can select a sound source to record: the popular SPDIF In, Line In, CD In, Aux and Mic, the less frequently used Wave and Mix, and the unique Alt. While Wave is a digital loop-back, allowing to record the reproduced sound with bit-per-bit accuracy, Alt is a bridge between the sound card’s line output and line input. This recording source can be useful for the reproduction of protected content (for which all digital recording sources must be disabled according to the license agreement). I could not check this out in practice, but found other useful applications for Alt. For example, the manufacturer recommends measuring the card’s parameters in RightMark Audio Analyzer using this source.

As you can guess, Mix joins the signals from all the sources together. That’s a nice opportunity, but it would be even better if the user could choose what exactly sources to mix and what to ignore. It is also somewhat inconvenient that the original recording level is achieved by setting the volume regulator to its maximum. To raise the volume of a quiet signal you have to use you sound-editing software. That’s why I could not measure the card’s parameters normally with headphones attached: the volume would drop by over 10dB under the low-resistance load and RightMark was unable to normalize the sound level whereas using a Creative card for recording produced incorrect results.

Well, that’s enough about the drawbacks. The card’s mixer has one very handy feature: the monitoring of every output. The buttons with the eye icon reproduce the signal from the appropriate input for auditory control – multiple buttons can be pressed simultaneously. I wish the “input selector” worked like that…

Well, let’s see what other features are offered on the other pages of the improvised menu.

On the Effect tab you can see fanciful settings of the environment (reverberation) effect and an equalizer. The developer’s logic is not quite clear here as he put four environment variants on buttons and left the rest in the drop-down list. When you select a variant from the list, you should press a fifth button to enable it. The lack of the option to adjust the reverberation intensity is annoying. You may want to have more echoes in games, but you won’t get it. Just be satisfied with what you have.

The equalizer is tiny. It is virtually impossible to set the necessary parameters with it. And its operation is questionable, too. I tried to lower the volume of the 4kHz band but could hear no changes in the sound. And when I lowered the slider to its bottommost position, I realized the 4kHz band had been cut out completely. I could only restore that frequency back by resetting the settings with the Default button. The saving of the user-defined equalizer settings is implemented in a non-intuitive way. You have to type in the name of your profile in the text field below and press the “+” button. Pressing the “‑“ button removes the saved profile.

I guess the equalizer deserves a separate menu tab especially as there are no timbre controls many users are accustomed to.

The Karaoke tab offers three settings: music tempo, voice muting, and an echo effect for the microphone. The purpose of these settings should be clear to everyone who has ever sung karaoke.

So, let’s move on to the next, very interesting, menu item called FlexBass.

Just as the name of the option suggests, you can flexibly distribute the bass among the speakers. The cross-over slider determines the threshold below which all frequencies are sent to the subwoofer and are cut out from the small-size channels. For large speakers, low frequencies are not cut off.

The cross-over is high quality, ensuring a symmetrical slope by 36dB and bringing no distortions into the sound.

The two bottom buttons, AEC and VocalFX, have appeared but recently in the driver.

The Acoustic Echo Cancellation mode is meant for video conferencing and other voice communication via the Internet. It disables all processing effects and tries to suppress the sounds that enter the microphone from the speakers. A brief test of this mode proved its high efficiency.

I guess it would be handier to have the AEC setting as a button in the bottom right corner of the Xonar D2 Audio Center where the sound processing presets are grouped because this setting is in fact represented by one On/Off checkbox.

The last tab, earlier called Magic Voice, offers a few additional features for processing the microphone signal. You can change the voice timbre (male, female, cartoon, monster), apply one of the four environment effects, and enable a special effect for games.

VocalFX applies reverberation to the gamer’s voice as determined by the game for the gamer’s current location. This feature was introduced by Creative Labs in EAX 5, and now ASUS can proudly claim that its product supports the competitor’s most modern technologies. You’ll see shortly if it is really so – in the gaming tests. Right now let’s take a look at other, hidden, parts of the driver. At its ASIO support, for example.

ASIO is a special interface for transferring data into the sound card with a specified delay. It is used in most sound-editing software. The Xonar D2 provides full support for ASIO 2.0 with 16-bit and 24-bit data precision and frequencies of 44.1, 48, 96 and 192kHz. Besides, the driver supports such an exciting feature as ASIO multi-host thanks to which several programs can work with ASIO simultaneously. The card doesn’t adjust the frequency automatically. If the frequency differs from the base one, the signal is recalculated using a high-quality software resampling algorithm. For comparison, the Creative X-Fi begins to switch the generator’s frequency in this case, clicking with the relay.

The Xonar’s ASIO implementation might be called perfect if it provided for paralleled recording of more than one source and supported a few additional reproduction channels (the Creative X-Fi has 18 such channels, for example). To remind you, the C-Media Oxygen HD audio-controller employed on the Xonar D2 allows recording eight streams simultaneously. It would also be handy if the ASIO settings screen could be opened from the Xonar D2 Audio Center.

I nearly forgot to tell you about one more original feature of this sound card. Upon installing the driver, you can see two new audio devices in the system: ASUS Xonar D2 Audio and ASUS Xonar D2 Converter. The latter device is meant for a quick application of effects to musical recordings. If you use an MP3-player and you like the spatial effect produced by Dolby Headphones or Virtual Speaker technologies or if you just want to correct the sound with the equalizer, you can run the included program called ASUS Portable Music Processor to re-encode your favorite recordings in MP3 and WMA formats with any special effect available to the driver.

I guess you’ve learned enough about the sound card’s potential. It’s time to check its practical qualities.

Listening to Music

The Xonar D2, a very top-class product, will be compared with the best non-professional sound cards available today, Creative X-Fi Elite Pro and Auzen X-Fi Prelude 7.1. To evaluate the sound quality I use Grado SR 325i headphones together with a C.E.C. HD53R Ver.8.0 amplifier connected to the sound card with a Monster Standard Interlink 200 cable. I use recordings of various genres saved from CDs in wave format. My players are Foobar2000 0.9.5 and WinAMP 2.95. The same volume (2dB RMS) is elected for every sound card in order to get the largest dynamic range. I disable the replay gain in the Foobar options; the sound is reproduced via DirectSound in 32-bit format. WinAMP is used together with the ASIO output (dll version) 0.67 SSE2 plugin.

I describe the versions and options so thoroughly because I noted in the Auzen X-Fi Prelude 7.1 review that not all players or sound output plugins could reproduce reverberations and the spatial localization of sounds correctly. My setup is more or less correct. The choice of the software player is important for sound cards of such a high class. For example, the version 0.9 ASIO playback plugin for Foobar works inaccurately which can be easily demonstrated with measurements.

Intermodulation distortions when reproducing sound 
via ASIO with different players. Digital loop, 44.1kHz, 16 bits

My first experience of listening to music on the Xonar D2 with the included driver was not very pleasant. Its sound was overall very clear and detailed but lacked the necessary depth and saturated overtones. I’d call this sound faded, colorless. The sound scene was broad but flat, without echeloning, which deprived the music of all the pleasure. Fortunately, the programmers found the error and it’s all much better with the current driver.

The card is admirable for its deep and dynamic sound. I am very impressed at the reproduction of minutest details against a loud background, which is especially conspicuous in the rich sound of violins, also in a large orchestra. The timbres of other musical instruments are quite natural as well; the medium and high frequencies are clear and detailed, the bass is sharp and saturated. But with all these advantages, the sound sometimes lacks space and aftersound, and the natural reverberations are quickly lost in the overall “mass”. So when there are many instruments playing simultaneously, you often feel the music is not really detailed. You can hear this quite distinctly in comparison with the Auzen X-Fi Prelude which is very delicate about the acoustics of the environment. The space, the realistic voluminosity even for the bass, the superb detailedness and microdynamics in the top register which yields highly natural timbres, make the Prelude the best choice for jazz and other live recordings. The Xonar differs from the Prelude with harder top frequencies but better macrodynamics, which makes it preferable for listening to Judas Priest, for example.

The Creative X-Fi Elite Pro sounds energetic and very detailed but its stiff and developed bass is accompanied with biting high frequencies while its medium frequencies are unexpressive and colored: after the ASUS Xonar D2 most instruments seem to play half a tone higher. The colorings from several instruments mix together to create a kind of a high-frequency coating worsening the spatial resolution. The reflections of high-frequency sounds from the walls of the studio recorded in the composition lose their individuality and merge into the original sound producing an odd result. I heard such unpleasant sharpness and aggressiveness before on my good old Audiotrak Prodigy 7.1 which still resides in my PC thanks to one accidental discovery.

Reading through the documentation on the Wolfson WM8770 digital-to-analog converter I noticed how greatly the digital filter characteristics varied at different sample rates. I tried software resampling (SSRC) of recordings into a sample rate of 192kHz and then into 176.4kHz (a multiple of 44.1kHz, the standard sample rate of music). I was highly pleased at the result: the sharpness disappeared, the scene became larger. With such a sound I didn’t want a more expensive sound card! Later on, when I dared to replace the opamps, I found an interesting thing: resampling didn’t provide any advantages with opamps faster than the default NJM4580. The Creative X-Fi Elite Pro has NJM2114 opamps, similar to the NJM4580 in characteristics, in its front output, so I decided to try software resampling once again.

Creative’s X-Fi series cards do not support the highest sample rates in the Audio Creation mode, so I had to limit myself to 96kHz, but that was enough for the situation to improve. There is less coloring and the high-frequency coating nearly vanishes from the scene. Medium frequencies are more detailed. First I used resampling in the ASIO output plugin for WinAMP but later I just set the necessary clock generator frequency in Creative’s mixer settings utilizing the card’s hardware resources for the process. The result was the same. In the Entertainment mode where stereo recordings are always converted into 192kHz, with the equalizer, Crystalizer, CMSS and SVE disabled, I achieved an even clearer and lush sound at the expense of a minor loss in spatial precision.

But in my previous review I noted that the Auzen X-Fi Prelude 7.1 behaved differently. Its precision degenerates without improving the other characteristics. Thus, I recommend you to stay in the Entertainment mode for listening to music if you have a Creative X-Fi card and don’t want to change the chips on it. Hardware conversion into another sample rate is implemented very well on the X-Fi, and the resulting sound is better than with bit-per-bit playback at the clock generator frequency of 44.1kHz.

But what about the Xonar? Can it benefit from resampling if it’s got a mixture of NJM2114 and RC4580 chips on its front output? I tried to switch the frequency selection option in the ASUS Audio Center at first but couldn’t hear any clear difference. The vocals only got muddier in some recordings. Then I tried to use WinAMP with the ASIO output plugin and my doubts left me: the resampling into 192kHz with the Ultra quality gave me the space the lack of which I noted above. It makes the high frequencies softer and more detailed and adds some more dynamics. The differences are not as conspicuous as with the Creative X-Fi Elite Pro but quite noticeable.

The same plugin helps measure the sound of the rear outputs which use the same DACs but three RC4580 opamps on each instead of the front output’s two NJM2114, one LM4562 and two RC4580. Has this cocktail a reason? It has indeed. Without resampling, there is a loss of detail on the rear channels, the high frequencies are fuzzy, the bass is not deep. But all these things improve greatly when you resample into 192kHz: the rear channels are still inferior in high frequencies and bass but I would appreciate them higher than the front output as concerns medium frequencies and the overall openness of the sound. The combination of three types of operation amplifiers in the front output makes it sound somewhat gloomy and cramped.

By the way, I can tell you a few interesting facts from the life of the ASUS Xonar. When you set the analog output into 2 Speakers mode in the Audio Center, the signal for the rear outputs is mixed into the front channel even if you use ASIO. On the contrary, if you select a multi-channel configuration but do not enable Dolby Pro Logic IIx or DTS Neo: PC technology, a stereo signal with a sample rate of 44 and 48kHz transferred through the Windows audio interface (including ASIO) is duplicated in the rear channels. For some reason the sound volume is lowered by 3 and more decibel for every interface, save ASIO, in the multi-channel mode.

The subjective description might have ended at that if it didn’t dawn upon me to check out the quality of the audio cables included with the ASUS Xonar. When I connected the sound card to the amplifier with one of them, I had to perform the tests once again because the sound became different: smaller details got clearer, the room acoustics became more realistic. There was the space that had been lacking. The coloring of medium frequencies disappeared. Surprised at that, I checked out a few more cables and each differed from the others. And I had to listen to each sound card again with five different cables.

After long experiments I came to the conclusion that the Monster Interlink 200 cable I had used before ruined the Creative X-Fi Elite Pro with its already sharp sound. When I used the cable enclosed with the C.E.C. amplifier the coloring and high-frequency problems disappeared although the cymbals and the sibilants in vocals still jarred on the ear. It was overall more comfortable, yet the card revealed its full potential in the Entertainment mode only: the stereo panorama got broader and more natural. The medium frequencies were clear and detailed. The high frequencies remained somewhat too gaudy, though. The ASUS Xonar sounded better with the included cable as it had less coloring and better microdynamics. The card easily coped with music of any genre, even with such complex classics as the infernal dance from Stravinsky’s Firebird, and the Story of Prince Kalendar from Korsakov’s Scheherazade. In the overture from Verdi’s Macbeth many sound cards fail to cope with the women’s choir, transforming the voices into indistinct deafening shouts. The Xonar not only separated each voice in space but also played the whole composition without any distortion which would make me lower the sound volume. Still, the ASUS Xonar is not ideal. My preference lies with the Auzen X-Fi Prelude as soon as it comes to lyrical compositions. Its way of reproducing music has something that I haven’t found a name for. It is a tenderness that attracts you, a softness that doesn’t make you tired. Interestingly, the Auzen X-Fi Prelude is the only card not to suffer from the Monster Cable although another tester I called for assistance from could distinctly tell between the cables even with this card.

For those who don’t believe that the cable can affect the sound of your equipment, I publish the measurement results for the chain Creative X-Fi Elite Pro → cable → CEC HD53R → ASUS Xonar D2. The amplifier was connected to the sound card’s line input with a very short cable with two mini-jacks.

Having checked each sound card with dozens of musical compositions, I have to confess there is no clear leader among them. Each card has it unique character. With a good audio cable the Creative X-Fi Elite Pro can sound superbly in Entertainment mode, being just as good as the ASUS Xonar D2 in terms of details and size of the sound scene. The Auzen X-Fi Prelude 7.1 is inferior to both its opponents in terms of macrodynamics but surpasses them in natural timbres and aftersounds. The ASUS Xonar D2 seems to me a golden mean in terms of bass reproduction. It has a fantastic resolution, but its medium and high frequencies are somewhat synthetic (this effect reduces when you use resampling into 192kHz).

The last step of my aural tests was the operation of the card with headphones without an additional amplifier. To remind you, ASUS declares a high-quality headphones buffer in the Xonar D2. In fact, it is a front output cascade based on paired general-purpose opamps, identical to those employed on the step of conversion and filtering of the three additional analog outputs. However, the buffer does its job well, making the card sound excellent even with the Grado headphones whose impedance is 32 Ohms. It’s hard to hear the difference from an external amplifier: there are just fewer details, a smaller depth of the scene, but the stereo panorama doesn’t get any worse as is the case with most sound cards that are not meant to connect to headphones directly. On the downside is the lack of power of the operation amplifiers. At 100% volume the output signal voltage drops by over 10dB when you connect your headphones. As a result, there is no reserve of volume even with highly sensitive headphones. Of course, you can lift up the individual volume controls of each channel in the Xonar D2 Audio Center mixer but then you’ll hear the volume lower distinctly at the first notes of a musical composition.

Playing Games

After Creative Labs devoured Aureal Semiconductor, the question of choosing a gaming sound card had only one answer – SoundBlaster. The software implementations of 3D sound procedures from Sensaura and QSound were inferior in quality (in terms of the frequency and dynamic range of the processed sound) but also put a heavy load on the CPU. But today, when there are two or even four CPUs in each gaming computer, the computing power is not a problem, giving a second chance to software solutions.

The Xonar D2 being based on a processor and driver from C-Media, the engineers took it easy: 3D sound is created by means of C-Media Xear 3D 7.1 Virtual Speaker Shifter technology which specifies the spatial position of 8 virtual speakers. The sound scene is rendered to them using Sensaura CRL3D HRTF 3D positional sound enhancement with multi-drive. 3D sound is down-mixed into stereo using technologies from Dolby Laboratories: the sound of a virtual 5.1 system is emulated on two speakers by means of Dolby Virtual Speaker technology. The same technology for headphones is called Dolby Headphone. You can visit the Dolby website to learn more about these technologies.

Originally, like any other non-Creative product, the Xonar D2 supported a reverberation model compatible only with EAX 2, but ASUS reported support for EAX 3, 4 and even 5 starting from driver version 8.17.30. Thanks to that, you can use OpenAL in Quake 4, for example, although the programmers still have to work on compatibility with other games. Not all applications identify these capabilities. For example, neither the RightMark 3DSound Positioning Accuracy test nor F.E.A.R. permit to enable EAX Advanced HD in the settings, at least in the Windows XP environment. And the card could only pass 3DMark03’s sound test when I disabled the GX feature. By the way, what is GX?

As you know, the DirectX 10 concept doesn’t allow manufacturer-specific extensions. Each DirectX 10-compatible device must support all of the standard features. EAX extensions version 3, 4 and 5 were only supported by SoundBlaster series products – they didn’t comply with the concept and were outlawed as the result. For games to use their specific DirectSound3D extensions in the Windows Vista environment, Creative’s programmers had to implement the substitution of DirectSound procedure calls with calls to their proprietary OpenAL library. Interestingly, a few years ago, the company created an emulator of OpenAL functions via DirectSound to make OpenAL popular among game developers. And now they had to do exactly the opposite.

The programming people from C-Media and ASUS made the same thing for the Xonar D2 calling it DirectSound3D Gaming Extensions. The difference is that DirectSound calls are translated into Xear3D rather than OpenAL, which is emulated by the card, too. The latest version of the driver features the second-generation DS3D GX with a reverberation model that simulates EAX Advanced HD and with the option of applying gaming reverberations to the microphone signal. The substitution of DirectSound calls is now performed in the Windows XP environment, too. On clicking the GX button in the Xonar D2 Audio Center the difference between DirectSound3D Software and DirectSound3D Hardware disappears because in both cases it is the Xear3D sound engine that works. This is necessary for the current implementation of OpenAL which is based on the generic hardware driver of the above-mentioned library for emulating Creative’s OpenAL. We can expect some improvements in OpenAL support in near future because the latest driver contains a file called Cm_Oal.dll which is yet not used in any way.

As you see, it’s all right about the gaming capabilities of the ASUS Xonar card. It supports all the necessary functions and offers options for adjusting the sound to your preferences. You only have to make out how all of this works. Not having a multi-channel speaker system, I limited myself to checking the cards’ ability to create 3D sound in headphones. Well, it is anyway handier to play with headphones because no one around you hears the shooting and shouts and asks you to lower the volume.

I got acquainted with the ASUS Xonar D2 when the demo version of Crysis game was released. So, I’ll begin with this super-hit. Crysis uses a software sound engine FMOD_EX which is independent from DirectSound3D but allows using EAX effects. Strangely enough, there are serious differences in sound between the ASUS Xonar and the Creative X-Fi. It begins right from the first screen where the disc with the Electronic Arts emblem appears with a screech. This screeching is already volumetric on the Xonar as if the disc is hanging in the air right in front of you. The X-Fi “draws” it flat, in your head. In the game proper, with Dolby Headphone and Dolby Pro Logic IIx features enabled, sounds from all directions are combined realistically, creating a natural picture of the ambient world whereas the background music, sounding from nowhere, adds more impressions. A low-flying jet sounds true, provoking an instinctive urge to bend down. Ricocheting bullets and exploding splinters are very realistic, too. At similar settings (CMSS-3D Headphone mode) the SoundBlaster X-Fi sounds absolutely different. After the change of the sound card you can hear more high frequencies but suppressed medium and low frequencies. The X-Fi delivers better high frequencies and reverberations, thus being better at reproducing open spaces, but it doesn’t provide the feeling of presence and drive you get from the Xonar. It seems like there is total silence around the gamer while the life goes on nearby – but the in-game music is reproduced right in your head. This synthetic acoustic accompaniment has a negative effect on your gaming experience, of course. I personally cannot prefer the X-Fi. It is scarier and more exciting to play with the ASUS Xonar. The difference in frame rate between these two cards cannot be caught subjectively. The test in a standard demo with a flyby of the island at the lowest graphics quality settings and maximum sound quality settings produces the following results (frames per second, average/minimum/maximum):

As I already noted, the latest driver from ASUS makes it possible to enable OpenAL in Quake 4. The improved audio engine the game acquired with one of the patches had been available for owners of Audigy 2 and X-Fi cards before, so I was eager to compare the quality of 3D sound in the laboratory-like conditions of the steel passages of Quake 4. Loading a few saves from different levels I was surprised to hear the Xonar D2 being quite competitive against the SoundBlaster X-Fi again! First of all, I noted its superb reproduction of the direction and distance to the sound source. The aural perception was in full agreement with the visuals. It was only when I looked straight at some object that small turns to the left or right would lead to unpleasant jump-like changes in the sound. Under the same conditions the X-Fi positions sound sources behind you more accurately but moves them about more than necessary on small movements of the game character, provoking an aural disorientation. Besides, it proved to have an odd problem with high frequencies – the hiss of steam and flares doesn’t get quieter with distance. It just stops at a certain moment. The X-Fi yields louder reverberations but I wouldn’t call them more natural: the X-Fi sounds better in one situation but the Xonar proves to be more natural in another. The sound of shooting is not as sharp on the Xonar as on the X-Fi but has a curious timbre. The Xonar is better at reproducing explosions. The X-Fi has more detailed high frequencies. Besides reverberations, the X-Fi can realistically calculate the reflection of sound from walls. When the ElevationFilter option is enabled, it can also reproduce the cannonade over the dungeons more naturally and load the CPU less. Still, I would prefer to play Quake 4 with the ASUS Xonar D2 if the latter were stable with the latest version of the driver (8.17.31 RC01 beta). Each time I had to move from one room to another through an opening door there were problems with sound and the game would quit with the error message “The memory could not be read.”

S.T.A.L.K.E.R. is yet another game that uses OpenAL to create a realistic acoustic environment. And this game was merciless to the Creative X-Fi. Added to the above-mentioned inaccuracy about the direction to the sound source was the incorrect reproduction of the distance to it. It is especially conspicuous for high-frequency sounds. For example, the grunting of bandits running at a distance sounds like you are already surrounded and about to be beaten hand to hand. Of course, this spoils your gaming experience. The ASUS Xonar D2 is quite another thing. It provides a fantastically sharp and natural acoustic picture for a complete submersion into the game world. It’s when you are shooting at a sound and always know how many people are alive behind your back. The wind is howling in your ears, the horrible roar from somewhere makes you shudder, and the bullets buzzing and banging against the steel chassis of abandoned cars make you hurry away from the line of fire even if you don’t see the enemy. I’ve never felt such a realism of gameplay, not even in the famous and awards-covered Crysis. There is almost no performance hit from the software processing of 3D sound. Selecting the lowest graphics quality settings, I had the following average frame rate in the demo record of a flyby of one of the game levels:

The last game I tested the cards with seems to have been optimized exclusively for the SoundBlaster with its EAX Advanced HD. It doesn’t notice the support of this technology in the ASUS Xonar and its sluggish samples sound well only on the SoundBlaster. No wonder the SoundBlaster is on the winning side. In the test record for measuring the frame rate, it provides more space, a more accurate localization of sounds, and nice reflections of sounds from the walls. Anyway, the ASUS Xonar D2 did quite well in the actual gaming situation, delivering a very realistic acoustic environment. Although the sounds of shots were dull and early reflections could not be heard, it was easier for me to orient in the heat of a battle with sly bots when I installed the Xonar. I didn’t spot an increase in the CPU load while the integrated benchmark produced the following numbers (frames per second, minimum/average/maximum):

Summing up my long experiments with games, I should acknowledge the progress ASUS has made with the driver and the Dolby Headphone technology which is superb for DirectSound3D-supporting games. In every game I have tried it with, this technology provided a more natural interpretation of the gaming environment than Creative’s CMSS. On the other hand, I have to point at the drawbacks of the current implementation of 3D sound: there is no calculation of early reflections, no processing of the vertical position of the sound source, very high intermodulation distortions at high frequencies that make the sound muddy and dull. If C-Media’s programmers get rid of the distortions, ASUS’ Xonar cards will make serious opponents to products from Creative Labs in games.

Objective Test Session

This section is the last one in this review so that the nuances I mentioned when listening to the card could be verified objectively. I tested the card using RightMark Audio Analyzer 6.0.6 Pro. This software reproduces a set of test signals on the given audio device and analyzes the result. The usage of the program is described in the official user manual.

To test the analog section of the sound card, a line output is connected to the line input of the same or other card (as specified for each table) with a short cable with mini-jack connectors.

Testbed configuration:

Before measuring the analog section of a sound card it is necessary to make sure that the driver reproduces the test signal correctly, without processing it in any way. I choose the Wave sound source in the sound card’s mixer and start one copy of RightMark Audio Analyzer to record the signal with the maximum precision (32 bits). Another copy of the program is reproducing test signals with a precision of 16, 24 and 32 bits through all the available output interfaces. By the way, this test is possible thanks to C-Media’s programmers who have solved the problem of incorrect processing of Wave sources that used to provoke lots of distortions.

A 16-bit/44.1kHz signal is reproduced without distortions through any of the card’s interfaces. The results for ASIO exceed the theoretical capabilities of the format. It is the consequence of an error in the Analyzer’s reproduction procedure. When played via WinAMP with the ASIO plugin, the signal coincides with the test sample.

Every interface seems to deliver the 24-bit test signal correctly, but when I examined the noise ceiling with a high-level tone, I found that the Kernel Streaming interface was the closest to the original although DirectSound and MME hardly differed from it. ASIO introduced some distortions which were not present when the signal was reproduced with WinAMP.

Even the prehistoric Wave Out copes with the reproduction of 32-bit signal if you use the latest version of the Xonar driver. DirectSound even manages to surpass the theoretical limit of the dynamic range but the measured level of noise and the crosstalk indicate that the driver performs some rounding off beyond the 24-bit precision. Perhaps it is the consequence of the conversion into floating-point format for the volume controls and resamplers.

The ASIO result is the same as with the 24-bit signal. That’s why I can make a supposition about the error with ASIO in RightMark Audio Analyzer. C-Media allows two variants of ASIO, with 16- and 24-bit precision, whereas other developers’ implementations support 16- and 32-bit precision as more convenient for the CPU. The benchmark developer must have not provided for this.

Interestingly, the Kernel Streaming is somewhat worse here than the reference interface, too. The picture below shows the spectrum of the recorded signal in the dynamic range test to illustrate the driver’s behavior:

Dynamic Range Test Spectrum

Now I will measure the quality of the analog section of each card. First, I’ll find out what card has the best line input. For this, the line output must be measured through the card’s own line input as well as through another card’s.

The ASUS Xonar and the X-Fi Elite Pro deliver similar quality, the Xonar D2 being but slightly better in terms of noise. But I had to choose a PCI slot with lowest power noise (it was the bottommost slot of the mainboard) while the Xonar D2 had the same results irrespective of the slot.

Connecting one card to another worsens the measurement results, so the following tests will be performed using the card’s own line input. First I’ll examine the front and rear channels of the two cards. To remind you, they only differ with the opamp models.

The ASUS Xonar D2’s front output only differs from the one of the Creative X-Fi Elite Pro in terms of intermodulation distortion. The same goes for the rear outputs. Of course, the numbers make the Xonar D2 the winner but I learned in my tests of the Auzen X-Fi Prelude that a better number doesn’t necessarily give a better sound.

So let’s compare the levels of individual harmonics.

Xonar D2 Out 1 (Front) Distortion Spectrum

Xonar D2 Out 2 (Rear) Distortion Spectrum

X-Fi Elite Pro Out 1 (Front) Distortion Spectrum

X-Fi Elite Pro Out 2 (Rear) Distortion Spectrum

The front output of the Xonar D2 shows a significant difference between the channels. The level of harmonics in the left channel is about 10dB lower but there is no fifth harmonic in the right channel. I don’t know the reason for that, but the rear output doesn’t behave like that. However, the rear output is worse even than the worst of the two front output channels. The line output of the Creative X-Fi Elite Pro is also worse in the level of the third and fifth harmonics, and its seventh harmonic is higher by over 10dB. As a result, the Xonar D2 wins the competition of the main outputs but Creative’s rear channels are better.

Now let’s see how the measured parameters of the two cards vary depending on the sample rate:

Xonar D2

X-Fi Elite Pro

The Creative X-Fi doesn’t allow to record 192kHz signal, so I don’t perform the test in this mode. It’s clear anyway that this card differs from the Xonar D2. The best results in terms of noise and dynamic range are obtained at 96kHz. Moreover, the Xonar is inferior in these parameters at 44kHz, too. Is it a problem with reproduction or recording? I’ll perform another measurement using another card’s line inputs.

It’s clear that the Xonar D2’s reduction of the dynamic range at a sample rate of 44kHz has nothing to do with its ADC but comes from the reproduction section. Is it the reason for the improvement in music playback after software resampling? As I found earlier, the driver correctly transfers digital signal with 24-bit precision, so the problem roots deeper, in the DAC interface or clock generator. Hopefully, ASUS and C-Media will deal with that just as they got rid of the intermodulation distortions in the earlier version of the Xonar D2 driver.

The same test for a sample rate of 96kHz:

Comparing the noise parameters with the previous results, you can see that the ADC in the Creative X-Fi Elite Pro works best at a frequency of 96kHz whereas the same ADC in the ASUS Xonar D2 ensures the largest dynamic range at a frequency of 44.1kHz. If it were not for the annoying problem with the reproduction at this rate and if there was a smaller difference between the left and right channels of the front output, the results of the ASUS card would be even more impressive.

If you want to scrutinize the measurements results, here are the RightMark Audio Analyzer saves.


The ASUS Xonar D2 is one of the most universal sound cards available on the market. The highest quality of technical implementation helps it deliver best results among mass products in performance tests. It is great at playing music, provides superb 3D sound in games, and has a highly functional driver. The quality of sound effects and the useful additions like the automatic encoding of multi-channel sound into Dolby Digital and DTS formats will please even a demanding user. Of course, the lack of a Linux driver may be considered a drawback, but if the sound card is used in a multimedia computer running Windows Media Center Edition, the Xonar D2 driver will install a special version of the control panel optimized for viewing on a TV-set.

The support for MIDI devices, the superb implementation of ASIO 2.0 and the high digitization quality of the analog inputs make it suitable for professional use in sound editing applications. If you want to try your skills at composing music, the card comes with a set of professional applications with somewhat limited functionality. The only downside is that you cannot record multiple sources simultaneously although the card’s heart, the C-Media Oxygen HD controller, supports that.

The copy of PowerDVD 7 and lots of accessories for connecting the card to an amplifier or receiver is a plus, too. If you prefer headphones, you don’t need an additional amplifier because the card copes with low-resistance load quite well. But if you don’t have a reason to plug your headphones right into the sound card, the additional cascade of mediocre opamps will be disappointing because it worsens the sound quality but doesn’t make the card less sensitive to the audio cables. By the way, the included cables are long and good enough – you don’t have to replace them.

I won’t sum up the pros and cons of the Xonar D2 as it would mean repeating the body of this review. My main gripes are about the Xonar D2 Audio Center, actually. The card is universal, making it hard to name its target audience exactly. Its strong point is in the highest quality of the analog outputs, which makes it preferable for a home multimedia center with a top-class multi-channel speaker system. Home DVD players with comparable hardware would cost much more than this sound card.

As for improvements I hope for, I really want a Deluxe version of the card with an even better Burr Brown PCM1792 DAC and high-quality opamps on the front output.