ASUS Xonar Essence ST/STX soundcards Follow-Up, September 2010

John Atkinson wrote again about the Xonar Essence STX soundcard in September 2010 (Vol.33 No.9):

When I reviewed this $200 soundcard for Windows PCs in the January 2010 issue, I concluded that the Xonar Essence STX was by far the least expensive way of turning a PC into a genuine high-resolution audio source that I had encountered. Neither the Essence's resolution nor its low level of noise was compromised by having to operate in the electrically unfriendly environment of a computer chassis. However, I ran into a problem playing files with sample rates of 96 or 192kHz. The card was installed in a quiet Shuttle PC (AMD Athlon 3.1GHz dual-core processor, 2GB RAM) running Windows Vista Home Premium with SP2. Using Foobar 2000 (v.0.9.6.9) or Adobe Audition 3.0 and setting the appropriate sample rate with the Xonar Audio Center control program didn't produce sound from the STX card that was noticeably better than standard CD-sourced files. It appeared that 96 and 192kHz files were being downsampled by the STX to 48kHz, with spectral components higher than 48kHz aliased into the audioband; eg, a 40kHz tone was reproduced as 8kHz.

I managed to solve the problem by downloading, installing, and then selecting either ASIO4.DLL or WASAPI as the default sound device in Foobar's Playback Preferences dialog. I let ASUS's technical support know about the problem, but they had not gotten back to me by press time for the January issue. In the new year, however, I did hear back from them: A beta version of a new driver was available that fixed this problem. I installed the new driver in the Shuttle PC, which by then had been upgraded to Windows 7. The original driver was v.6.12.8.1762; the new beta driver was v.7.12.8.17731, dated 2/3/2010. The original version of the Xonar Audio Center software was v.0.2.3.20; the new one was v.0.2.3.27, though the appearance of the user interface was identical (fig.1).

Fig.1 Xonar Audio Center user interface.

With the new driver, bit-perfect playback by the STX card is guaranteed at all sample rates supported by the DMA buffer—44.1, 48, 88.2, 96, 176.4, and 192kHz—and, unlike with the earlier driver, ASIO-compatible applications take exclusive control of the audio device. However, the card's volume control is disabled when it is used in this mode, which makes it inconvenient for headphone listening.

With the Xonar Audio Center open and playing files with Foobar 2000, selecting "Speakers (ASUS Xonar Essence STX Audio Device)" and 24-bit resolution in the Foobar Output Preferences dialog now did give true 96kHz playback, a 40kHz tone being decoded as 40kHz. However, material recorded at 88.2kHz was still sample-rate–converted to whatever rate had been chosen with Audio Center, the 88.2kHz sample rate not being available.

Changing the preferred output device to "Xonar Essence STX bit-perfect ASIO driver" and choosing "Digital Output (ASUS Xonar Essence STX Audio Device)" in Windows 7's Control Panel/Hardware and Sound/Audio Devices dialog did give the correct sample rate for the file being played at the digital output. I tested this configuration with data having sample rates of 44.1, 48, 88.2, 96, 176.4, and 192kHz, and bit depths of 16 and 24; in every case, the data output by the Essence STX were identical to those in the original file. I tested this by recording the output to a new file, inverting its polarity, then playing the old and new files simultaneously in Adobe Audition 3.0. They nulled completely, confirming that the data were the same.

Fig.2 Xonar Essence STX, eye pattern of S/PDIF data output carrying 16-bit J-Test signal (±500mV vertical scale, 175ns horizontal scale).

Tested with the digital input of the Audio Precision SYS2722 as the PC played the 16-bit Miller-Dunn J-Test data, the Essence STX offered low jitter, even with a TosLink connection, at 690 picoseconds peak with a correspondingly clean eye pattern (fig.2). However, I did find one anomaly with the Essence STX's digital output. I was playing files on one PC, feeding the soundcard's TosLink optical output to an RME soundcard fitted to another PC so that I could monitor the state of the bits in the digital datastream using RME's DIGICheck program. To my surprise, when I paused playback, instead of all bits changing to zero (which is what usually happens with digital sources), the DIGICheck meter indicated with red flags that some bits were still active (fig.3). Recording the STX's digital output with Adobe Audition showed that the data remained latched at the value of the last word of the audio data before playback was paused, resulting in a digital DC offset (fig.4).

Fig.3 Xonar Essence STX, bit status of digital output with playback paused.

Fig.4 Xonar Essence STX, waveform of digital output before and after playback paused.

I was at first alarmed by this behavior—if you happen to pause playback just when a waveform peaked at its maximum possible level, the resultant DC offset will be equivalent to a full-scale signal. But this offset is in the digital domain; it would present a problem only if it translated to an equivalent DC offset in the analog domain, where it might be amplified by the power amplifier, with possible damage to the loudspeakers' woofers if the entire playback chain was DC-coupled. I tried the Xonar soundcard's digital output with every D/A processor I had in the house, ranging from the budget-priced Benchmark DAC1 to the super-expensive dCS Puccini. In every case, when I paused playback on the PC, the resultant digital offset did not give rise to an analog offset. Even when I deliberately arranged for the latched data in the Xonar's digital output to be equivalent to a full-scale signal, I couldn't measure any related DC offset in any of the processor's analog outputs. So while this behavior is curious, it isn't pathological.

Headphone listening
I didn't have the space in the original review to discuss the Essence STX card's sound quality with headphones, though I did say that the fact that the headphone output's maximum level could be adjusted to match the headphone impedance was a blessing. The output impedance of the ¼" headphone jack was 10.7 ohms at all frequencies and settings, which is usefully low. However, there was a relatively high DC offset on this output, at 19mV left and 15mV right, this unrelated to the anomaly in digital output noted above.

Through my favorite headphones, Sennheiser's HD-650, I was consistently surprised by the quality of the Xonar soundcard's output. Yes, in comparison with the CEntrance DACport USB headphone amplifier ($395), which I reviewed in June (p.99), the highs weren't quite as silky smooth; and my reference Benchmark DAC1 ($995), fed with the Essence STX's digital output, offered tighter, deeper lows and a generally greater feel of dynamic swings. For example, Mark Flynn's snare drum on Attention Screen's Live at Merkin Hall (CD, Stereophile STPH018-2) exploded from the Sennheisers as it should when the headphones were driven by the Benchmark; driven by the Essence STX at the same level, the drum sounded as loud, but without quite the same jump factor. The low frequencies did have a greater feeling of power and drive than they did with the DACport, however, and backgrounds were silent, with no noise interference from the PC. Overall, the Essence STX's headphone output was better than you would expect from so affordable a product.

As we prepare this issue of Stereophile for publication, I'm working on the first mixes, using Adobe Audition 3.0 in multichannel mode, of the concert Attention Screen played last April at the Yamaha recital hall in midtown Manhattan (see "Update" in this issue). Whether listening to the mixes through the Sennheiser headphones driven directly by the Xonar soundcard or via the card's optical output fed to my big rig, I get no sense of missing anything that I should be aware of.

Summing Up
With its driver update, the Xonar Essence STX and its PCI-bus equivalent, the Xonar Essence ST, can be recommended to those on restricted budgets who wish to incorporate a PC into their high-end rigs.—John Atkinson

COMPANY INFO
ASUSTeK Computer Inc.
US distributor: ASUS Computer International
44370 Nobel Drive
Fremont, CA 94538
(812) 282-2787
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COMMENTS
Xavier Xerxes's picture

John,

Thanks for your review.  I would like to use the digital and analog output connections at the same time: digital for my home theater 5.1 experience and the analog to be connected to a 12-zone amplifier.

 

Is it possible that both digitial and analog output signals can work this way?

 

Thanks!

Andrei's picture

I am running two of these beasties.  One an ST and the other an STX.  For my part I have never had a problem with either playing resolutions of 44.1, 48, 96, & 192.  Sound quality was already good and took a giant leap forward when I upgraded the op-amps (a very cheap exercise).

Now the tricky subject of resolutions of 88.2 Khz and 176.4 Khz.  In fact there is a workaround.  If you have the free Audacity software it can be done.  Audacity is one of those freeware programs that are just outstanding.  What you do is this: (1) you simply load the track to be played.  (2) you play it back in Audacity.  So you do not use Foobar or MediaMonkey or Windows Media player or the like.  Now here is the curious thing: when using Audacity for playback it actually sounds better than even Foobar, my current favorite.  Audacity is a progarm for manipulating sound, rather than playback, but it naturally has a playback feature so you can hear the effects you have done.  What I think is happening is this:  Audacity rips the track into memory as some sort of wav format and hence the bit-rate / resolution is no longer relevant.

While I am on this subject: I found a small improvement by running a co-axial into a dedicated DAC.  This is not really necessary and hardly justifies the expense because the Xonar ST and STX already have excellent DACs.  The cost is a lot because you will need not only a better DAC but the cabling has to be good too.

Mirko's picture

Thanks for the great and informative review.  I bought this sound card with the intention of streaming spdif out to my pioneer 09tx so I could listen to high def FLAC on my stereo system.   I had no idea that the quality of the card actually makes a difference when using spdif out.  Which is contrary to what most people write about spdif.  Often you read that it doesn't matter and that bits are bits.  But i found this actually isn't the case.  If you don't believe me, try for yourself.  I thought I could live w/ my motherboards Realtek spdif out to my receiver and let the receiver  do the decoding.  But noticed that My realtek spdif sounded like crap!!! ESPECIALLY when comparing against the sound files the receiver decoded from usb or the ipod dock.  So I considered an external DAC, but I know that my receivers dac uses wolfson 8741 chip which Is already good. Anyway, after hooking up this asus bad boy, i was blown away by the worldly difference in sound that it made.  Setting the output on the card to PCM 192khz and I'm all set.  Mission accomplished.  But that's not all.  After comparing the analogue sound of the card, i was again, quite impressed...which one did i like better? My receiver to decode or the asus PCM chips?  i did A/B comparison with the asus doing the decoding versus the pioneer by running a long 1/4" jack and setting the volume level the same between the two.  Let me tell you, for 200 dollars, this asus card does a seriously good job providing a crisp clean and open analogue signal to your ears. I still prefer the my receivers dac by wolfson chips.  The sound is a little more smoother and less harsh to my ears..it's different but not better.   But I killed two birds with one stone on this one.  For two hundred dollars I got an excellent digital transport to my receiver, and high end audio analogue outs from my computer that are clear, clean an extremely quiet.  Very happy customer here.  To think that there are people out there running spdif from  crappy cards to thousand dollar external DACS is sad to me.  Maybe I'm wrong..anyway.  Awesome card.  Awesome buy.  Killer sound.  Makes me wonder if I would be able to discern the difference from this card and the essence one.  

Mirko

Andrei's picture

Hi Mirko

I agree the sound quality is really good.  My other Source is a Cambridge Audio 650BD (not counting a turntable). Overall the Asus Xonar ST eclipses it by a tad.  The comparison is a bit tricky though because (i) I have upgraded the op-amps; (ii) the CA 650BD does play DVDA and SACD.  But on an Apples to Apples Comparison CD vs Flac at 16bit 44.1 Khz : the Asus Xonar card is a smidge better.  It becomes even better when I play flac files at 24bit and 48, 96, and 192 Khz.  On the other side the CA650BD is a bit better when playing DVDA and especially SACD.  The CA 650BD is not high-end to be sure but it is not bottom end either.  I think for 'spare change' the Asus Xonar cards are simply fabulous.  Why anyone would buy a Music Sever when they can have this card?

Initially I used the RCA connections direct to the AMP.  Then I tried SPDIF optical, and USB into an external DAC.  Finally I tried SPDIF coaxial into an external DAC.  USB was easilly the weakest and SPDIF via co-ax is easily the best sound quality.  The caveat is that you do need good cables.  

Andrei

Andrei's picture

Oops.  Ignore the USB comment above.  I actually have two of these soundcards, or rather an ST and an STX.  With the STX that I use in my office it is connected to Bowers and Wilkins MM1 Desktop speakers.  They have the USB connection option to the PC.  With this Soundcard I connect via a RCA to Stereo plug.  It is this USB connection that I had tried and is not as good as using the Asus Xonar soundcard.

Andrei

hollowman's picture

Selecting 192k Sample Rate in Xonar's Audio Control Center gives best performance of std. 16/44.1 in my tests. Wish the Control Center allowed more direct DAC control, such as selectable digital filter (Slow/Sharp) and phase reversal. 

Agree that this Card is a decent value. Since Asus decison-makers (and Asus' direct competitors, like HTOmega) are probably reading these comments, here are three suggestions for future products:

1. Use dual DACs in diff mode

2 Use better DACs, such as ESS Sabre

3. Design/offer more advanced firmware filters (prefer. user selectable) and upsampling. This may be via decoder DSP or simply selecting amongst those innate in DAC chip. E.g., Min. Phase, Apodizing, etc. Also allow selectable upsampling.

That's all! #3 requires no costly PCB/topological redesign -- it's just software code re-writing. #1 and #2 can be done w/o too much PCB redesign. The Sabre chip maybe $20-30 more, but I'll be glad to pay that for the huge gain in performance.

Thx for your attn.!

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