Two in One: Asus Xonar Essence STX Sound Card Review

A sound card with a high-quality headset amplifier is an excellent gift for music-lowers. But how good is it in reality? You will find out from our extensive review!

by Sergey Romanov
06/04/2009 | 04:27 PM

Concluding my review of the first product from ASUS’ sound card department Xonar D2, I wished there had been a Deluxe version of it that would have employed the best-quality digital-to-analog converter from Texas Instruments called PCM1792A. When I was writing that conclusion, there had already been released the PCI Express version of the card, Xonar D2X and the two low-profile cards Xonar DX and D1 were getting ready to be announced. They used a design with a top-quality front output and lower-quality rear channels. As time went by, there was no information about improved versions of the Xonar D2 and D2X. A few months later, there appeared news on the Web about two HDMI-oriented sound cards from ASUS: Xonar HDAV1.3 and HDAV1.3 Deluxe. Was it the Deluxe I had waited for? No. When I scrutinized the specs, descriptions and photographs, I saw that the analog section of those cards differed from the Xonar D2 only in the opportunity to replace OpAmps without soldering. Quite disappointed, I gave up keeping track of ASUS’s new sound products especially as there was in fact no news about them for a while.


It had been a lull before a storm, actually. The first news on the Xonar Essence STX really stormed through the newswires, leaving only totally deaf people indifferent. ASUS did more than I had expected: stereo outputs only, premium-class converters (a PCM1792A DAC and a CS5381 ADC), an integrated headphone amplifier based on the enthusiast’s choice TPA6120A2 chip, and electrolytic capacitors that had earned an excellent reputation in audio equipment. It is hard to believe but the Xonar Essence STX has absorbed nearly everything best from what is being discussed on audio technology forums. Now you can imagine how anxious I was to hear its sound. And here it is: a stern black box with a reproduction of an Ancient Chinese engraving and a message to audiophiles…

Package, Accessories and Specifications

Flipping the box cover back, I found a detailed description of the design and key features of the sound card that I saw lying below the transparent window. The description makes a particular mention of the PCM1792A digital-to-analog converter and the TPA6120A2 headphones amplifier, independent power supply of the analog circuits, meticulous screening of the outputs, multi-layer PCB design called Hyper-grounding, replaceable operation amplifiers and special Nichicon “Fine Gold” capacitors.

The box is actually a fount of wisdom about the product it contains: the back panel is occupied by a table that lists the key product features in as many as 12 languages. The side panels describe the card’s technical parameters, box contents, and system requirements. The spread shows a photo of the card with the functions of all of its connectors indicated. The box gives you the complete lowdown on the device, actually. The included brochure is just a multilingual installation guide and offers little info besides what you can read from the box, yet I learned from it that the microphone input had a high-quality pre-amplifier. A more detailed user manual can be found on the included disc or at the manufacturer’s website.

The pretty booklet designed with a hard cover and decorated with gold lace offers a report about the test of the line output and line input of an early sample of the card that was carried out on the 6th of October on a professional Audio Precision testbed. I won’t dwell upon the results here. As you can guess, the results would not be published with such pomposity if they were not exceptional. The same numbers can be seen in the product specs, actually.

As opposed to the Xonar D2/D2X, the manufacturer has not included any cables for connecting the card to an amplifier or receiver. There are only three adapters: a Y-shaped adapter from RCA connectors to a mini-jack, a headphones adapter and an optical cable adapter. This is quite enough, actually, yet I guess a high-quality RCA-RCA cable would be quite appropriate.

Besides, the box contains a small poster that narrates about a 4000-year-old search for perfection and the realization of ancient wisdom in combination with cutting-edge technologies that endows the Xonar Essence STX with the highest sound quality a sound card may have. Here is this quality expressed in numbers.

Indeed, the specifications are unprecedented for sound cards, and even professional external audio interfaces may be inferior to the Xonar Essence STX. I will certainly check if the card meets its specifications, but the next section is about its hardware.

Hardware Design

Let’s have a look at the card’s design and components.

Interestingly, the ASUS Xonar Essence STX has no mini-jacks typical of most other sound cards. The line output is implemented by means of consumer RCA connectors. The line-in and headphone outputs are stereo 6.3mm jacks, making the cards similar to both semiprofessional products like the ESI MAYA44 or Infrasonic Quartet and consumer cards like Audiotrak Prodigy 7.1 HiFi and Prodigy HD2. It does not have a digital input but offers a separate headphone output that is enabled by choosing the appropriate mode in the card’s control panel. The line input is combined with the microphone input but you can connect the microphone and headphone interfaces to the connectors on your system case. Besides FP_audio, the card has two useful onboard headers: AUX_in and SPDIF_out. The connectivity options look good to me and I’ve never had any problems with them.

The card needs additional power via a standard Molex connector (like the connector you use for PATA drives). ASUS’ engineers claim that the PCI Express x1 slot cannot ensure enough current to power such high-quality components as are installed on the Xonar Essence STX and is too susceptible to current ripple and electromagnetic interference. While I do not agree with the latter statement because I have faced the need for additional filtering of power for devices connected directly to the computer’s power supply (the external module of the Creative X-Fi Elite Pro or the Scythe KamaBay Amp), there is no denying that a reserve of power is needed for the integrated headphone amplifier.

There are two 270µF SANYO OsCon capacitors near the power plug that make it somewhat difficult to insert the connector into the latter. The other electrolytic capacitors are all marked as Nichicon. Both brands are well known to everyone who is interested in developing audio equipment with high sound quality. Practice suggests that capacitors can influence the subjective reproduction quality of a device very much. Electrolytic capacitors with solid dielectric have earned a good reputation for their acoustic properties as has been proved in the previous generation of sound cards (Auzen X-Fi Prelude and ASUS Xonar D2). However, specialists still prefer aluminum electrolytic capacitors of special types in premium-class equipment; therefore it is good that two kinds of such capacitors are employed in the Xonar Essence STX. I will try to find any subjective difference later on.

The burnished screen you may have seen on the ASUS Xonar D2 covers about one half of the card’s PCB, leaving not only the digital section, which does not need any screening, but also all the electronics of the line/microphone input exposed. Besides, the lack of a slant in the corner of the screen makes it impossible to fix the card screwlessly in system cases where add-in cards are fixed by means of plastic locks.

There is a PCI → PCIe bridge from PLX Technology in the bottom right corner of the card. It acts as an intermediary between the peripheral bus and the card’s main chip marked as ASUS AV100. I don’t know what differentiates it from the ASUS AV200 that was installed on the Xonar D2, but both chips have the same specifications.

Internal signal switching is done by small electromagnetic relays from NEC. Like in the Xonar D2, the line input is based on a CS5381 analog-to-digital converter with NJM5532 operation amplifiers. I can remind you that this ADC is the topmost model in Cirrus Logic’s product series and is somewhat superior to similar products from Asahi Kasei (AKM) in its declared parameters. The digital-to-analog converter is an improved version of the Burr-Brown PCM1796, which did well on the Xonar D2 and some other devices like Audiotrak DrDAC2. The PCM1792A features Advanced Segment architecture and current outputs, differing from the PCM1796 with an improved output filter, lower distortions (especially at a sample rate of 44.1kHz) and a larger dynamic range (127dB and 132dB in stereo and mono modes, respectively). I compared the distortions of these two converters in my Xonar D2 review, so I will just show you two graphs that illustrate the advantage of the PCM1792.

PCM1792A Digital Filter Response:

PCM1796 Digital Filter Response:

I want to dwell upon the implementation of the analog outputs in more detail. The lack of a separate headphone output was a serious drawback of the Xonar D2. In the Xonar Essence STX the outputs are not only separated physically but there is a special headphone amplifier based on a TPA6120A2 chip from Texas Instruments. This is a second sound card I can recall (after the HT Omega CLARO halo) that employs such a high-quality amplifier. The chip is a high-power current-feedback opamp that features distortions of less than 0.001% at a 32Ohm load. When the load is lower, the distortions are lower than 0.0001%, which is comparable to the best opamps of today.




Judging by the specifications, this is the highest-quality serially produced single-die amplifier for headphones. Better characteristics can only be achieved by means of composite circuits with discrete components. On the downside of the high-speed nature of this opamp is that an isolating resistor must be employed, which leads to worse damping and increased low-frequency distortions with low-resistance headphones.


I can note that ASUS used the circuit recommended by Texas Instruments in which the TPA6120A2 sums the balanced output signal of the DAC. Depending on the mode selected in the control panel, the electromagnetic relay switches the signal from the I/U converter either to the line output opamp or directly to the headphone amplifier chip.

Typical circuits for TPA6120A2 and PCM1792A:

The three line output opamps are the same NJM2114 and LM4562 that were used in the Xonar D2’s front output but inserted into sockets for easy replacement (as the text on the product box says, this can be done to adjust the card’s sound to your taste). Frankly speaking, in such a top-end sound card as the Xonar Essence STX I’d prefer to see six soldered-in high-speed single-channel amplifiers rather than DIP sockets which may affect the stability of high-speed opamps.

Testbed and Methods

The sound card was tested on a PC configured like follows:

The version 1762 driver was installed without a hitch and I saw the familiar ASUS Audio Center icon in the system tray. Its functionality is 99% identical to what was described in my ASUS Xonar D2 review, so I will only dwell upon the features unique to the Xonar Essence STX.

It is a shame that in the year and a half the Xonar series has been available on the market the developer has not corrected any of the unified control panel’s drawbacks. The volume control still does not react to the mouse wheel. There are still no peak meters in the mixer, and the sound recording level is still limited to 100%, which is highly inconvenient for people who tinker with sound recording amateurishly.

You can see that there is no option to choose a speaker configuration other than two channels. Does it mean that the user will not be able to reproduce 5.1 sound even via the digital output? The user manual says the opposite but it is full of obvious mistakes. For example, the description of settings mentions the opportunity to record from an SPDIF input and to output audio via HDMI but the Essence STX lacks such connectors! The recommendation to connect your headphones to the line output because the latter allegedly contains a top-quality headphones amplifier is a mistake, too. I checked it out and found no headphone amplifier on the line output.

If you choose headphones as the playback device (the main or front-panel ones), you can select one of three gain settings: 0dB (< 64 Ohms), +12dB (64-300 Ohms) and +18dB (>300 Ohm).

I can only make guesses as to what the decibels are counted from here because when you select the first variant, the maximum output level of the headphones amplifier proves to be lower than the line output signal, which is 2V. And when the second variant is selected, the max output resistance is higher than that. I guess it is the absolute amplification coefficient that equals 1, 4 or 8, respectively. By the way, the headphones resistance ranges specified in ASUS Audio Center should not be viewed as mandatory. You should choose a higher amplification coefficient only if you really feel you don’t have enough sound volume.

It is very sad that the volume control does not differentiate between the output modes. In other words, it does not remember the volume level for headphones and speakers individually. You can hurt your ears and damage your headphones if you forget to lower the volume when needed. After I had a light contusion once, I learned to check out the position of the volume control beforehand.

Odd as it may seem, the Xonar Essence STX does not support DTS Connect and DTS NEO:PC that have been available in every previous model of the Xonar series. Of course, their functionality duplicated the capabilities of Dolby Digital Live and Dolby Pro Logic IIx but the opponents from Auzentech and Creative, on the contrary, have been learning how to encode sound into DTS format. Also odd is the fact that when you choose the Headphones mode and enable Dolby Headphone, the option of turning Dolby Pro Logic IIx on is available, but the latter disappears in the 2 Speakers mode.

The settings of the Dolby Pro Logic IIx department have undergone yet another staff cut. In the Xonar D2 review I wrote that only the first two operation modes were available out of the three (Music, Movie, Game). And now the Movie mode has been abandoned as well. To make the list of the control panel oddities complete, I can note that the Dolby Headphone technology processes sounds transferred via ASIO whereas the other technologies affect only Wave, DirectSound and Kernel Streaming.

Audio Center has lost the EAC mode that had been introduced into the Xonar D2 driver especially for video conferencing. Audiophiles don’t like to communicate via microphone? I don’t think so. By the way, the Xonar Essence has some problems with microphones: the monitoring of the microphone input is only enabled when microphone is selected as the recording source. When recording from the Mix source, the microphone signal is recorded quieter. I did not notice the high-quality microphone preamplifier promised in the user manual – the signal was quiet and, if the Microphone Boost option was turned on, noisy. You will have to use an external amplifier for a dynamic microphone.

While I had no problems making the Xonar Essence STX work in my system, I did not succeed in trying to install two Xonar series cards into it. ASUS Audio Center always preferred the Xonar D2, giving me no control over the Xonar STX, but both cards were dead silent when I tried to reproduce audio through either of them. When I turned the Xonar D2 off in the Device Manager and restarted ASUS Audio Center, the Xonar Essence STX became available and reproduced sound correctly. Thus, it is impossible to directly compare the two cards of the Xonar series and I will compare the ASUS Xonar Essence STX with the well-known and widespread Creative X-Fi Elite Pro.

Sound Reproduction Quality

Comparing the sound reproduction quality of audio equipment is the most difficult part of any review, especially when the differences between devices amount to a few thousandths of a percent as measured electronically. The subjective impression can be influenced by every trifle including the author’s personal predilection towards a specific manufacturer. Therefore I am very meticulous about everything I do before I listen to the devices and recheck myself and my impressions many times before I make up my final opinion, although sometimes this is still not enough.

If you have read my earlier reviews, you may have noticed that my subjective impression about the Creative X-Fi Elite Pro has been getting better with each new test session. It was totally routed by the Auzen X-Fi Prelude but earned my praises for dynamics and detailedness in the ASUS Xonar D2 review. Here, it will be compared with an even more advanced sound card and, running a little ahead, it will be quite competitive. This is no miracle. I am just steadily improving the test methods, particularly such nuances as cables and sound volume settings. In my previous reviews the resulting sound volume was determined by the analog volume control of the C.E.C. HD53R-80 amplifier and all the sound cards worked at the maximum of their capacity. But I had to adjust my method upon performing objective measurements. The amplifier’s volume control is now set at 12 o’clock, the amplification switch is set at the medium position, and the comfortable level of sound volume is set with the sound card’s Master Volume. These settings of the C.E.C. amplifier ensure a compromise between noise, distortions and frequency response.

I want to make one more digression before I get to the tests proper. Upon installing the Xonar Essence into the computer and listening to the first musical compositions on it (it was the XRCD version of Judas Priest’s Wings of Destiny), I realized it was a very, very good sound source. Out of curiosity I connected the amplifier to the card’s headphones output instead of its line output and found the sound to be much more transparent and clear! This impression was subsequently reconfirmed: the line output, implemented with RCA rather than with ordinary mini-jack connectors, delivered a somewhat turbid sound. It does not steal any details and does not spoil the sound scene, but it sounds somewhat sluggishly and makes the imaginable sound sources, especially high-frequency ones, somewhat muddy. It was quite noticeable in comparison with headphone output and X-Fi Elite Pro. Thus, the new card had a worthy opponent. Having made sure of that, I took to methodically listening to one musical track after another, comparing the sound quality of both line and headphone outputs of Xonar Essence with the Creative product.

The musical compositions were in WAV or APE (Monkey Audio) formats and were reproduced via foobar2000 0.9.6 with the ASIO plugin version 1.2.6. The sound cards were were tuned to the highest-fidelity mode: the X-Fi was switched into Audio Creation mode with Bit-Matched Playback and the HF mode was enabled for the Xonar. To avoid disturbance and minimize the time for switching, I used the adapters included with the Xonar Essence, reducing the three different output connectors to a single 3.5mm jack. Then, the sound was transferred to the C.E.C. HD53R-80 amplifier via a cable taken from the Xonar D2 box. A pair of Grado SR 325i headphones was connected to the amplifier’s right output.

The certain blurriness of the sound of the Essence STX’s line output is even beneficial for not-very-high-quality recordings which did not sound well when reproduced via the headphones output. In its turn, the headphones output offered a gorgeous sound in high-quality recordings: an abysmal depth, a crystal clarity, excellent dynamics, and lush overtones. The overtones are also rich in the Xonar Essence STX’s line output, making it better than the Creative X-Fi Elite Pro. The difference is especially conspicuous with the piano, violin and other musical instruments with a large spectrum of overtones. They sound listlessly on the Elite Pro and very natural on the Essence STX. In some cases the Elite Pro outperformed the line output of the Essence STX thanks to a better attack and a more detailed scene, but the status quo was restored as soon as I switched to the headphones output. Conversely, if the Elite Pro sounded somewhat softer and natural than the Essence STX’s headphones output, the latter’s line output proved to be even better.

This could be observed until I came to the What’s Wrong track from the Ecore – Best Of T.I.S. – Audiophile Sampler disc which was obviously reproduced better by the Elite Pro. The main difference was in the sound of the acoustic guitar when it being played with beats into the microphone standing nearby. Irrespective of the output I connected the amplifier to, the Xonar Essence created an annoying humming cloud in the left ear instead of the feeling of the musical instrument with strings and resonating case. This fact raised my earlier suspicions about the use of NJM2114 operation amplifiers on the I/U conversion stage that I had expressed in my ASUS Xonar D2 review. I had Texas Instruments OPA2132P and NE5532P opamps with appropriate DIP package and I decided to check out if the NJM2114 were to blame or not, especially as Texas Instruments recommended using the NE5534 and OPA2134 in the standard circuits for the PCM1792A and TPA6120A2.

The NE5532 being similar to the NJM2114 in its internal circuitry (the latter is sometimes even called a turbo-charged clone of the former), I did not expect them to differ much in sound quality. When I replaced one with the other, the problematic track began to sound somewhat better, at least there was less of the ear-straining hum, but one more track from the same disc, called Cowbell, made me take the sound card out of the computer again. The various drums and percussion of that composition jarred on my ear and the replacement of the NE5532 with the OPA2132 changed the situation dramatically. The sound scene became a single whole and roomier, and the minor tones and reverberations got clearer. It is like watching a scenery first in a water reflection and then – in a clear mirror. That’s the difference between the NJM2114/NE5532 and OPA2132 in the I/U conversion stage. The high frequencies of the Cowbell composition ceased to jar on my ear, the guitar in the What’s Wrong composition got more natural, and the overall sound was more exciting. This refers to the headphone output, though. The line output only got worse from the change: the previously sluggish sound became downright lazy. The bass grew flaccid and the trebles dull. Very much intrigued, I had to make a break in my test session to get some sleep, and the next day the Creative X-Fi Elite Pro refused to work.

Having lost half a day trying to install any driver for the unidentified Creative device the X-Fi Elite Pro had transformed into, I replaced it with an Auzen X-Fi Prelude that had been lying aside due to the total incompatibility of different X-Fi based devices with each other. This sound card had been praised for a very interesting sound, so I thought it would make a good opponent to the ASUS Xonar Essence STX. And when I listened to them, I was shocked because the Prelude was far better! Although the electric guitars of Judas Priest sounded as if from under a blanket and the piano lost its weight, the Prelude was otherwise much more beautiful and interesting, especially in vocals.

So, I took the Essence STX out from my computer again and put the NJM2114 back in place – these opamps had beaten the X-Fi Elite Pro in 90% of compositions. Indeed, when the change was made, the Essence STX became melodic and expressive but its drawbacks returned, too. These were somewhat colored mid frequencies, rather too hissing high frequencies, and a deep but occasionally thick bass. I would say that the default Essence STX provides a true Hi-Fi sound: it is very beautiful, with a broad sound scene, excellent dynamics, accurate reproduction, exciting expressiveness and detailedness. The Prelude, on the contrary, stifles the sound somewhat, is inferior in the naturalism of the timbres of stringed instruments but ensures a more concerted bass and puts less emphasis on sibilants and other fricatives. When listening to the set of test compositions on the two cards, each third composition sounded better on the X-Fi Prelude. When the NJM2114 was replaced with the NE5532 again, the tonal balance of the Essence STX grew so similar to the X-Fi Prelude (including the mentioned stifled quality) that they could only be told apart by smallest nuances – I often could not decide what card was actually better. In some cases I would prefer the Prelude due to the difference in the sound of the high frequencies but the Essence STX would become superior at a reduced sound volume because it would maintain its detailedness and pleasant total balance. The biggest difference in favor of the Essence STX was observed in the Raising Sand album by Robert Plant & Alison Krauss.

Thus, I could not find a universal replacement to the DIP-case NJM2114 but I know where to look for. I have unverified information that the OPA2134 differs for the better from the OPA2132 in the I/U stage, and Texas Instruments uses it in the typical connection scheme of the TPA6120A2. The AD8066 might make an ideal choice but it is not produced in DIP packaging. And ideally, this position should be occupied by an opamp like THS4631. But is it necessary to replace the LM4562? Having performed a number of tests with the Auzen X-Fi Prelude, I returned to the original LM4562. As a low-pass filter it ensures the most realistic timbres and best detailedness. Neither OPA2132/2134 nor AD823/826 could provide the same combination of properties. Therefore, the LM4562 in DIP packaging can only be replaced with SOIC --> DIP adaptors that extend the choice of opamps greatly. Then you can try the LME49722 or the single-channel opamps of the OPA827 class.

Now I must tell a few words about the headphone amplifier integrated into the Xonar Essence STX. Besides a separate output that makes it far easier to use, it features good reproduction quality. I listened to a number of compositions, switching the headphones from the sound card’s connector into the C.E.C. HD53R-80 amplifier connected to the same output of the Xonar Essence. The low impedance of the Grado headphones is a difficult test for amplifiers and the TPA6120A2 specs suggest that its distortions grow up under such load, but it was hard for me to notice a difference in the sound of the two amplifiers. Besides some discrepancies in the sound scene that are hard to describe in words, I can note the more natural sound of the piano and the clearer trumpets on the C.E.C. amplifier. The difference was more conspicuous with Tchaikovsky’s 1812 overture: the TPA6120A2 gets less detailed at spectrally dense moments, its high frequencies becoming muddier and its bass being less controlled, but these are all minor drawbacks you can hear in but a few compositions. I liked some tracks better as reproduced by the TPA6120A2 but the C.E.C. was overall superior with the 32Ohm headphones. You should not forget the much higher cost of the external amplifier, though. The availability of numerous high-quality headphones with 250 Ohm impedance opens wide possibilities for the integrated amplifier of the Essence STX.


High quality of music playback is good but gaming is also a popular kind of entertainment. Can the ASUS Xonar Essence STX deliver good sound in games, too? I compared it with an Auzen X-Fi Prelude while passing the same levels in a few games supporting 3D sound. Some of them were the same as I had used in my previous reports and I could hear right away that the gaming sound of the Xonar Essence STX was far different from what I remembered from my Xonar D2 tests. This must be due to the changes in the driver after the expiration of the license for the Sensaura algorithms. I won’t make guesses how they were employed in the Xear3D engine that is responsible for all the 3D sound capabilities of the Xonar series, but as soon as C-Media’s website published the announcement about the expired license, the exclusive DirectSound3D Game Extensions technology was updated in ASUS’s driver.

The first version of GX was meant only for Windows Vista and allowed to enable hardware mixing and EAX effects in games that did not support OpenAL. As opposed to Creative Alchemy, ASUS GX works for all games and does not do anything with the files: all the sound processing is done on the CPU. Other makers of sound chips have also introduced such features (Realtek 3D SoundBack and C-Media Xear3D EX) but ASUS went further. Creative Alchemy originally offered support for EAX 4 while the other manufacturers could only get the license for EAX 2. As a result, some modern games that are meant for EAX higher than version 2 refused to enable the maximum sound quality on Xonar cards. GX 2.0 technology became useful for Windows XP, ensuring basic compatibility with some EAX 3, 4, 5 features demanded by such games although it did not offer full support for the latest versions of EAX. For example, in my Xonar D2 report I wrote about a bug in Quake 4 that would occur on your passing from one room into another. I could not find a change list for GX 2.5, so I first wanted to see if the previously noticed problems had been solved.

And I could not find any difference. RightMark 3DSound and F.E.A.R. still do not allow to enable EAX Advanced HD and you cannot pass the Sound Test from 3DMark03 if the GX checkbox is set in the ASUS Audio Center. Quake 4 does not brake with a memory read error, though.

As I have noted already, the behavior of the Xonar Essence STX in games proved to be a complete surprise to me. The drivers with GX 2.0 have not been released for this audio card, so I will do an additional test of the Xonar D2 soon. Here, I will describe all the peculiarities I have noticed. Every game was set up for maximum sound quality which was the same for both cards.

In the previous test session the Xonar D2 was better in Crysis as it provided more vivid impressions on my turning Dolby Headphone on together with Pro Logic IIx. This time the old trick doesn’t work. When I turned Dolby Headphone on, the sounds of shooting were weakened and the spatial positioning of the sound sources was worsened. As a result, a massive exchange of fire was reduced to a mess of vague claps and cries. DPLIIx did not improve the situation and I despairingly tried to turn on the last of the options I had at my disposal: 7.1 Virtual Speaker Shifter. To my greatest surprise, this changed the sound dramatically. The feeling of distance and the sharpness of the shots was all there in an instant. Disabling DPLIIx, I enjoyed a sound environment that was adequate to what was going on on the screen, with good separation of sounds in space and with a low-frequency accompaniment of machinegun shooting.

According to the user manual, 7.1 Virtual Speaker Shifter is an extender of sound to 8 channels similar to Dolby Pro Logic IIx as well as a transformer of 7.1 sound to any number of speakers with the option of setting up the position of the virtual 7.1 speaker set. This option used to change the sound volume according to your changing the distance of the virtual speakers from the hot spot but did not affect the spatial effects. The sound volume can still be changed, but it grows up about twofold when you turn 7.1VSS on, making you use the Minus button in the settings. The most interesting thing is that turning 7.1VSS on and off without changing the position of the virtual speakers has no effect on the sound positioning in the RightMark 3DSound Positioning Accuracy Test that uses the DirectSound3D API.

Comparing the Xonar Essence STX with the above-described settings and the X-Fi Prelude in Game Mode, the X-Fi had a drier and more synthetic sound and did not yield the feeling of space the Xonar delivered. That was especially conspicuous at the moments a jet would fly overhead but the chirping of birds and other sounds of nature around the gamer produced the same feeling. The X-Fi seemed better to me at reproducing the sounds of human characters, though. The various whispers and clangs, voices and echoes were not so sharp on the Xonar even though the difference was not too big. I had almost the same frame rate with either sound card although I occasionally had a feeling that the gameplay was smoother in action-heavy scenes on the X-Fi Prelude. Thus, the Xonar wins this round by 3 to 2.

Next I tried the cards in Battlefield 2 which had not been used in my tests before. This game is interesting for offering a Creative X-Fi optimized mode that ensures maximum sound quality. Having passed two different levels with the X-Fi Prelude, I was very impressed as I could find not a single flaw to complain about. The Xonar is obviously inferior here, as you can see right from the intro video in which the female voice is distorted more. The Xonar lacks the fast attack that transforms each shot into a whipping blow to your eardrums but its overall quality (without Dolby Headphone) is comparable to the X-Fi’s. You can hear the echo from shots and the performance is almost at the same level. The only problem is that everything seems to be closer than it really is. Turning Dolby Headphone on corrects the distances but distorts the sound, muffling the special effects such as the whizzing of bullets. It is like having a plastic pail on your head. And again, the 7.1 Virtual Speaker Shifter option miraculously improves the sound! With this option enabled, the Xonar has only two noticeable drawbacks: the sounds subdue too quickly with the distance and there is a heavy performance hit. While the X-Fi allowed playing comfortably at a 1.8GHz processor frequency, the Xonar with enabled Dolby Headphone and 7.1VSS provoked jerkiness and hiccups in the headphones. The Xonar put such a serious load on the CPU in this game that the previously stable overclocked platform began to show a BSOD, calling for an increase of voltage on the memory modules. Thus, the Xonar lost that round with a score of 1 to 4.

Despite its venerable age, Quake 4 can still please you with good sound in OpenAL mode. The X-Fi is a treat to the ear with its splendid reflections of sound from the walls and the lush and perfectly positioned sound sources. However, even the latest version of the driver for the Auzen X-Fi Prelude does not correct the problem of nonuniform change of the direction to the sound source after “head” movements – I wrote about that problem back in my Xonar D2 review. If Dolby Headphone is not enabled, the Xonar Essence STX gives you no sense of direction towards the sound at all. The Gaming mode does not improve the situation much: the sounds are crowding in your head and disappoint you with their indistinctness. Fortunately, 7.1 Virtual Speaker Shifter comes to rescue again. When you enable it, you get the interesting sound of weapons I had noted with the Xonar D2. The environments grow up in size and it is impossible to find fault with the quality of spatial positioning. And the most important thing, there are no slowdowns or hang-ups. The only disappointing things are the lack of reverberations and the sometimes incorrect positioning of flare's sizzle when the next level is being loaded up. Therefore the X-Fi wins this test with a score of 3 to 2.

The last game I tried the sound cards in was a relation of both Quake 4 and Battlefield 2. Enemy Territory: Quake Wars differs from them with its ability to reproduce sound via both DirectSound and OpenAL. When I entered the s_driver console command of the dsound interface, I could not perceive a serious difference between the two sound cards. Moving in the Spectate mode on the battlefield, I could spot the direction from whence steps, shots or explosions were coming, but I did not get the feeling of total immersion. The cannonade was roaring in my head and the distance to the place of action was reproduced unclearly. When I switched to OpenAL mode, the X-Fi’s sound was nearly unaffected whereas the Xonar with Dolby Headphone and 7.1VSS could reproduced everything with incredible realism. The good thing about the X-Fi is that it could reproduce the Doppler effect of missiles flying over you. I could not hear the Xonar reproduce it. Anyway, the overall score is 2 to 1 in favor of the Xonar.

Summing it up, the 3D sound implementation on the Xonar Essence STX is not without drawbacks, but the X-Fi Prelude is not ideal, either. The Xonar was only defeated in a game that had been specifically optimized for the X-Fi. In the other games, the cards were roughly equal.

RightMark Audio Analyzer

Subjective impressions should be verified by unbiased electronics. I will do that with the unique software suite called RightMark Audio Analyzer 6.2. It measures a number of standard parameters of the audio section by reproducing and recording a set of special signals. You can refer to the official user manual to find detailed info about the use of RMAA for testing purposes.

To measure the performance of the two outputs of the ASUS Xonar Essence STX I had to use 6.3-->3.5mm and RCA-->3.5mm adapters so that I could have the same equipment as in the previous reviews. To remind you, in order to test the line outputs I use a very short cable connecting the sound card’s input and output. The headphones amplifier is tested using a special splitter that is connected to both headphones and the line input of the Creative X-Fi Elite Pro sound card. For details about our methods of testing headphones amplifiers you can refer to the Scythe KamaBay Amp SDA-1000 review.

I want to say my huge thanks to the Xonar Essence STX developers for not saving on the analog-to-digital converter. As a result, this card’s line input is no inferior to those of the X-Fi Elite Pro and Xonar D2. The quality of the line input is highly important for tests: the result cannot be better than permitted by the recording device. And if you use the line input of another sound card installed into the same computer, you will surely get a worse signal-to-noise ratio.

Before discussing the test results I want to note that the Xonar Essence STX proved to be highly sensitive to the purity of power supply despite the additional power connector and numerous high-quality capacitors. In order to get acceptable results on the line output I had to roll the power cord into a small coil or there would be a lot of parasitic noise in the spectrums. The headphone output was less sensitive, its spectrums being clear all the time.

Line Out quality on Xonar Essence STX

The specifications say that the line input has a SNR of -118dB whereas the line output is twice better than that. Thus, it is the line input that must have limited the results in terms of noise and dynamic range. But what about the distortions? They do not meet the declared specs and are inferior to those of the Xonar D2 and X-Fi Elite Pro! I then performed a series of measurements of the headphone output and was perplexed even more:

Headphones Out quality on Xonar Essence STX

Paradoxically, the headphone output proved to be much better than the line output and by far exceeded the specified level of distortions. Thus, the high level of distortions in the line output is not due to a low quality of the line input. There must be some other reason. I suspect the feedback resistors because my replacing the opamps had no effect on the measured characteristics. The distortion spectrums agree with my supposition.

Headphones Out distortions

Line Out distortions

Here we can see that the right and left channels of the line output differ greatly in terms of harmonics. The headphones output shows the same, making me suspect a large variation in quality between the passive components in the I/U conversion stage, but there is also a considerable increase in the highest harmonics in the line output’s right channel. Therefore, that variation is not limited to a single defective part.

I guess the measurement results explain the drawbacks in the reproduction quality of the line output in comparison with the headphones output. Now, it is interesting to compare the parameters of the headphone amplifiers under load. Subjectively, the C.E.C. HD53R-80 was often better than the integrated amplifier. Will this be confirmed by the measurements?

The conditions and methods are the same as described in our first amplifier review but with one difference: the measurement results had only been correct at an output voltage of 1V due to an error in the normalization of the recorded signal. The problem was corrected in RMAA version 6.2.2 but the death of my Creative X-Fi Elite Pro prevented me from rerecording the results at a lower volume.

As I have written above, connecting one sound card’s output to another card’s input almost inevitably provokes more noise if the cards are installed in the same computer. That’s why the dynamic range of all the devices should be considered as similar. This does not apply to the other measured characteristics.

The harmonic and intermodulation distortions of the Essence STX’s integrated amplifier at the 32Ohm load are no match to specialized amplifiers although exceed the capabilities of sound cards’ line outputs. The distortions are especially poor at low frequencies, although the output resistance is comparable to that of the Creative X-Fi Elite Pro.

By lowering the volume by a couple of decibel the distortions can be reduced by 50%. When the volume is reduced by 9dB (not shown in the table), the headphones output of the Xonar Essence STX becomes as good as the line output of the Xonar D2 in terms of intermodulation distortions, but 5 times worse in terms of harmonic distortions.

TPA6120A2 distortions spectrum at 32Ohm load

Fortunately, it is the second and third harmonics that contribute the most to the total harmonic distortion whereas the fourth and higher harmonics fall below -100dB.

In fact, Xonar's integrated amplifier at low impedance loads can only be praised for good channel separation, which is not achived with line output of any sound card I tested. By the way, I want to remind you that the high channel crosstalk at measurements under load results from the Y-shaped splitter made from a thin screened cable. Therefore you should disregard the absolute values of the Stereo Crosstalk parameter.

The TPA6120A2 specification says that its intermodulation distortions get much lower at a load of 64 Ohms and higher. At a load of 600 Ohms the total harmonic distortion is not higher than 0.0003%, so I have no doubt the integrated amplifier is going to show its worth with high-impedance headphones.


When I had been listening to the Auzen X-Fi Prelude, I had not expected any card to surpass it. Later on, the ASUS Xonar D2 showed the weak aspects of the Prelude. And now, the Xonar Essence STX sounds better than the Xonar D2 and Prelude, and better than the X-Fi Elite Pro, and perhaps even better than any audio card in the world, but I still want some more! It is a shame that the Essence is just one step short of being perfect. It just needs better resistors and different operation amplifiers.

Of course, everyone can try to pick up operation amplifiers to his/her own taste as the developer has provided for that. But why is not the card set up properly out of the box to deliver a SNR of 124dB and maximum sound quality? There is a lot of theory available on transimpedance amplifiers and suitable opamps are specially marked by their makers. And why is the odd problem with the noise level at 44.1 kHz not solved since the Xonar D2? Developing audiophile equipment means searching for the ideal. One should not take it up unless there are ways to achieve that ideal. Or should one?

Anyway, today, the Xonar Essence STX is the best choice for a person who wants to enjoy excellent-quality music, especially in 250-300Ohm headphones. It will also be good in games and may even prove superior to X-Fi based audio cards in some gaming situations. And finally, this audio card can be used for high-quality sound recording as it offers solid ASIO support. It also offers two outputs with different connectors and significantly different sound and is based on the modern PCI Express interface. Thus, I just can’t think of a worthy opponent to this audio card in terms of functionality and sound quality.

But still, what a pity it is that such a tiny gap distanced Asus Xonar Essence STX from being absolutely ideal...