Pros: Good size, laptop-portable, thick lush/sweet mids, warmer overall tone, fully fleshed-out bass range (no roll-off), good measurements in general
Cons: Will not work plug 'n' play, overly smooth sound, lacks quickness texture and bite in treble and bass regions, minor front headphone jack annoyances
Edit: It has come to my attention that this review was tested with a poorly performing newer official Asus Driver and therefore, the performance of the U7 here is not representative. I am confirming improved performance using a legacy WHQL certified driver. For any future readers, please consider this review invalid until further revision.
Kit Impressions: Asus Xonar U7 7.1 USB Soundcard - March 4, 2016
Soundcards have always been an intriguing thing. Many people argue that DAC/AMPs are better value in terms of pure sound quality. But it's generally all the bells and whistles and plethora of features and software features, that attract people to buy these soundcards. Whether this means 7.1 surround, virtual surround for gaming or something as simple as desiring a 10-band equalizer or even something like karaoke pitch changing for flexibility of sound.
If being able to "customize" your listening experience beyond being limited only to the signature of your headphones/earphones, DAC and AMP are the main features, these USB powered portable ones shine even more with their ability to be operated outside of PC internal noise and flexibility to be carried around some what like a laptop-portable DAC/AMP. This makes it easy for someone to get consistent sound quality using their PC at home and bringing it around with their laptop to work, especially if you are a musician or producer switching between machines but want consistent sound quality.
The unit appears to be mostly well built and solid with a fairly stylish gold accent "trim". On the inside there are no obvious signs of sloppy or poor soldering and such, according to many other sources.
The U7 does not look to have any kind of EMI shielding or barrier in between the enclosure to minimize electromagnetic interference, which is still fair considering this is an external card to begin with. The separated board on the Headphone and Microphone/Line is an interesting decision that should help with EMI from the main board itself to some degree.
Methodology & Setup:
Firstly, I don't have much experience in DAC/AMP combos, however as some might already know, this U7 is not plug and play at all and will not work without downloading and installing the drivers from Asus support. On the bright side, once installed it will work immediately with full functionality even without a reboot... although I would still recommend doing so to prevent weird driver issues.
And to note, since the physical volume controls of the mic gain, and massive gain knob are tied to Windows, you will also need to have the HID service enabled within Windows for the physical volume functionality to work, otherwise it wont do anything no matter how many RPMs you spin the knob around.
Everything was tested on a Windows 7 64-bit desktop PC through the U7's Headphone output exclusively, which is driven by the Cirrus Logic CS4398 DAC and the rear speakers I have not tested, by the Cirrus Logic CS4362.
So far, I have not experienced major problems with the drivers or anything. There are some annoying bits here and there regarding plugging in and removing headphones on the front jack.
For example, every time something is detected to be plugged in the front headphone jack, the U7 switches from the default speaker output to the headphone output and it immediately defaults back to speaker when unplugged even when no speakers are plugged into the rear RCA, SPDIF or 5.1/7.1 outputs.
This would normally not be a problem, however when you are playing any kind of audio when this happens, the drivers tend to temporarily "reset" or "forget" your impedance gain settings you defined by clicking the downward orange arrow in the driver panel headphone tab and will require you to pause or stop the audio playing to fix itself otherwise the audio might sound too quiet. Even worse, if you are watching a YouTube video and you unplug your headphones, YouTube's player will stop working and require a page refresh.
All of these are not deal breakers, but can make certain tasks like A-B testing (swapping out headphones) difficult and somewhat tedious.
As with being a soundcard, we also get some nice flexible features like the 10-band equalizer and other arguably less useful effects. You can generally expect that the features all in all don't feel like it's missing anything with the small exception of Karaoke Key/Pitch Shifting, which was present in my older Xonar DSX.
What was quite amusing in moderate doses was playing around with the Dolby surround feature plugin at the bottom of the driver panel, as it was in my opinion a more effective and engaging surround emulation than the default surround. The intelligent Equalizer on the Dolby panel was quite interesting too and offers somewhat more of a dynamic listening experience that's different than using a static equalizer setting. Sadly, you cannot customize the sound signature of the dynamic equalizer and can only pick from one of the 6 presets.
Even though the effects are often overkill they are still great to experiment with even if you generally like leaving everything turned off for a more pure listening experience like me.
DAC & AMP Sound:
Overall I can confidently say that this is one of Asus's more warmer/fuller/smoother sounding Xonar products, packing a fairly balanced sound at the same time. While the Xonar line is generally known for their value and neutrality in terms of sound, the U7 strikes me as sounding almost completely different than the Xonar DSX PCIE soundcard that I currently own.
For my personal tastes, I found that across the general frequency band that there was a certain lack of detail that seemed to be slightly veiled by the smoother signature. Where the smoother sound of the U7 sounds great to make the mid frequencies lush and sweet, the treble lacks the bite and convincing ring of live plucked string instruments and the bass seemed to lack speed and texture, although it is arguably one of the most extensive bass I have ever heard, capable of all the way down to 10hz and below!
This may be great for some people but, for others like me might prefer bass quality over quantity and even extension.
The amplifier, although not listed by Asus in the specifications, appears to use the Texas Instruments LME49726 dual channel operational amplifier. The U7 overall musters quite respectable a performance considering the USB driven power, driving my 60 ohm 105db SPL/mW earphones rather loudly even at 30% volume in Windows. Theoretically, the amp should have enough power to drive headphones up to 150 ohms. Unfortunately I do not have any proper high impedance headphones to test that theory at the moment.
One thing that is very important to note however, is that if your plugged in headphones sound too quiet, you should check the aforementioned gain limit setting by clicking the little downward-facing orange arrow in the driver panel headphone tab, a drop-down menu should allow you to select between a high, medium, or low impedance setting. There is no reason to put it on anything other than high impedance for maximum potential from the amplifier and forget about it, unless you are concerned that you might push 100% volume by accident and blow your ears out!
I've tried plugging in the U7 to different USB ports on my motherboard and tried the U7 with multiple IEMs and even a pair of 8 ohms speakers plugged into the same 3.5mm headphone jack and the overall consensus of the sound seemed fairly consistent. At first I was suspecting the output impedance of the headphone out was too high and caused looser bass performance through less damping giving a warmer overall signature, but I was not very sure until I ran a full volume RightMark Audio Analyzer for some simple loopback testing. Here are the results of the U7 (the first 4 slots) compared next to my Asus Xonar DSX:
No clipping occurred according to RMAA and for reference, the top 4 graphs represent the U7's frequency response performance at 44.1k, 48k, 96k and 192k. The side and bottom graphs are taken from the 48k results which were the card's best overall configuration/results.
Where the numbers may seem fine and even great for the most part aside from the rather below average IMD + noise %, the graphs can really tell a tale of what's going on sonically.
Although I cannot expect the output impedance of the U7 to be much lower than 10-20 ohms which is often the typical amount for these USB powered DAC/AMP/Soundcards, I doubt that's been causing the warmer signature by itself. You can evidently tell the slight dip in the low frequencies is where cheaper DACs or AMPs often tend to cut corners and roll off the bass, the U7 seems to overcompensate for this on the other end (which is still a lot better than rolling it off completely) by boosting the 50hz area and below significantly.
From the THD and IMD charts you can also tell that the lower frequencies also share the same boost and higher distortion further contributing to the signature tilting of the sound.
The bottom right corner shows alarmingly massive THD levels of distortion at the 192k testing, which is rather an unusable band if RMAA is telling the truth! However this distortion is also suspiciously present in my Xonar DSX results which could even mean a common issue with both of the card's line in.
By comparison these are the DSX's graphs:
Know that however, all of this RMAA testing is subject to and limited to the quality of the line input for the recording and also, since this was tested as a loop without a proper load, the results are not completely representative and are only a glimpse or better understanding of "why something might sound like it does."
Conclusion & Value:
I feel like the Xonar U7 is a fair proposition of size, decent portability (if you want to bring it around with your laptop), and it is very liberating to be able to get away from using a soundcard inside the noisy environment of your PC. And especially if your soundcard is slotted above a noisy buzzing and/or power hungry graphics card under load. The results of the Xonar U7 measured about a 10db improvement across the noise levels, dynamic range, and stereo crosstalk to my Xonar DSX too.
I will say one thing: sound is subjective and "in the eye of the beholder". The Xonar U7 is superior in the numbers overall but sound characteristic-wise the increased overall distortion in the bass region may be one of the many factors that made the signature to be a little too warm and thick for my personal tastes and a little lacking in treble quality. In comparison my DSX, even though measured overall worse sounded more clear, thin, transparent and analytical... especially in the highs. Or perhaps I am just used to that sound now.
Any way you put it, there's not many of these types of products, and the U7 could represent good value for those who are looking for a flexible/multipurpose DAC with integrated amp, specific features to use on their PC and as well, elsewhere like their own laptops. More and more products are starting to saturate this USB soundcard/DAC/AMP area in the times of still not-so-good onboard audio of laptops and even in those classified as "Ultrabooks". Only time will tell if the Xonar U7 is truly good value in the face of competition.
But that's just my thoughts. Happy listening!