Objective Reviews & Commentary - An Engineer's Perspective

March 1, 2011

NuForce uDAC-2 Drama

NuForce uDAC-2 vs Behringer UCA202 SoundDRAMA? (revised 3/16/11) Ok, so nobody is going to want the movie rights, but my experience with the NuForce uDAC-2 had some unexpected drama. When I started making measurements of the uDAC-2, it was doing so poorly on some tests, I stopped. Had I received a defective one? I contacted NuForce and sent some of my preliminary measurement results. That turned into 16 emails back and forth with NuForce finally concluding:

“Your uDAC-2 is within spec, and both of our measurements are correct, just that we are looking at different part of the plot. If you are going to publish your report, I appreciate that you also publish our response, which you will find that we did not dispute your finding, but it makes a compelling case why we TUNED  uDAC-2 this way.”

LISTENING TEST (added 3/16): Because NuForce has strongly argued they designed the uDAC-2 to sound good, despite the poor measurements, I set up two different listening trials to let anyone download the files and listen for themselves. The results can be found here: Nuforce Listening Test Results

JUST TO BE CLEAR: I have no other experience with NuForce, and I’m in no way affiliated with any of their competitors. I just bought one of their DACs for my personal use. There’s no hidden agenda here and the subjective comments are only my opinions. The measurements are readily reproducible (and many were verified by NuForce themselves).

DESIGN BY EAR? (added 3/9/11) Apparently, based on comments regarding my measurements from Jason Lim the CEO of Nuforce, the company prefers listening to measuring. For example, in response to this review, Mr. Lim posted a public comment (that he references in the comments section of this article) that includes: “better sounding product still win hands down over better measured product” and “If someone choose to listen with their measurement equipment, there is nothing we can do.” Here are my observations:

  • THIS HAS HAPPENED BEFORE: NuForce’s “listen first” design philosophy hasn’t always worked out so well. Thanks to Mainelli’s comment at the end of this article, I learned (3/9/11) John Atkinson at Stereophile used an Audio Precision analyzer to measure the NuForce CDP-8 last year. He found the NuForce to have among the highest amounts of jitter he had ever measured, as well as unusually poor noise modulation and predicted the sound of the CDP-8 likely suffers as a result. Interestingly, I also measured very high jitter with the uDAC-2.
  • NuFORCE’s RESPONSE: Jason Lim from NuForce responded to the Stereophile Measurements by saying NuForce believed the performance was “addressed by the design”, they made “decisions based on listening”, and “the measurement was a surprise to us” because it seems they never measured the jitter, or likely the noise modulation, themselves.
  • SURPRISES: Apparently my measurements were also a “surprise” to NuForce—just like the ones made by Stereophile. I am concerned when companies that claim to offer superior products don’t even seem to bother (or perhaps have the capability) to measure their basic performance. You can take the finest DAC chips and other components in the world, throw them on a great looking PC board, wrap it in a fancy high-end enclosure, and you will likely get very poor performance. Jitter and noise performance, in particular, are very sensitive to the PC board layout, grounding issues, EMI, etc. So if you don’t properly measure your product, you really don’t know what you’re going to get. And, it’s my opinion, that’s what happened with both the uDAC-2 and the CDP-8 tested by Stereophile.
  • TOTAL PERFORMANCE: The ultimate performance is not merely “addressed by design” as Mr Lim is quoted in the article. That would be like Boeing delivering airplanes without ever testing them because they were confident in the design and the plane simply “felt good” to the pilot. As the multi-year delays with the Boeing 787 Dreamliner show, there are many problems that often don’t show up until you conduct the right tests.
  • ANOTHER “DESIGN BY EAR” EXAMPLE: I bought a power amplifier from a high-end manufacture similar to NuForce in some ways. After I started listening to it, the tweeters failed in the speakers it was driving. I measured the amplifier and discovered an overly protective current limiting circuit (triggered by my 4 ohm speakers) that created nasty high frequency bursts of powerful and inaudible noise. It was these bursts of ultrasonic noise that destroyed the tweeters. And in contacting the manufacture, much like with NuForce, they seemed completely unaware their amp had a problem. All they could talk about was how it sounds great and pointed to subjective reviews (without measurements) that also said it sounded great. Well, unless perhaps you’re a dog, you can’t hear a 25 Khz burst that destroys tweeters—that requires proper testing and measurements. Their amp, like NuForce’s DAC, also didn’t meet its published specifications and apparently had never been properly measured.
  • WHY “DESIGN BY EAR” OFTEN DOESN’T WORK: In my experience, most companies who “design by ear” to varying degrees also don’t believe in blind listening tests. Whenever their equipment is subjected to a blind test, and doesn’t do well, they are very quick to provide reasons why such testing isn’t valid. Consequently, they usually don’t conduct their own blind listening tests. Instead, they use “sighted” listening. And it’s been widely shown sighted listening is significantly flawed, biased, and misleading. If you’re skeptical, please see some of the links in the right hand column of this blog such as Dishonesty of Listening Tests. So, in summary, it’s fairly safe to say most of these manufactures who “design by ear” are designing in a way that’s signficantly flawed and biased. All the proof is already out there. It’s not the best way to design equipment—especially if you also skip making proper measurements as NuForce apparently has.

WHICH USB DAC? I needed a small, USB powered DAC for headphone use with a secondary PC. Here are some I considered and my thoughts on each:

  • Behringer UCA202 – My first idea was the Behringer UCA202 as I already had one laying around and it’s nice and small. So I wired it to the dScope to check it out. It measured surprisingly well in almost every way—impressive enough I decided to turn it into a UCA202 Review. But, unfortunately, the headphone output impedance was too high for my preferred headphones. Strike one.
  • E-Mu 0202 – I also had an E-Mu 202 already. But a quick check showed the headphone output impedance is 22 ohms. That’s a better number, but still not low enough to work well with my preferred headphones. The E-Mu is also kind of big to try and hang off the back of a slim all-in-one panel PC. And it needs its own proprietary driver that has caused problems on some PCs. Strike Two.
  • M-Audio Transit – The Transit is well regarded, small, and I also already had one. But, sadly, while M-Audio claims the 3.5mm Line Out jack also works for headphones, it has the same 50 ohm impedance as the Behringer UCA202. It also, like the E-Mu, needs its own potentially troublesome driver. Strike three for what I already owned.
  • FiiO E7 – The $99 E7 gets some good reviews and is relatively popular. It uses a digital volume control to supposedly maintain good tracking between the channels. It can also act as an analog headphone amp, has built-in EQ and an optional desktop “dock”. But, from what I read, it forces the Windows volume control to maximum. While this delivers a bit accurate stream, if I want to mount the DAC on the back of the PC so using only the up/down volume buttons on the E7 wasn’t a viable option.
  • Firestone Audio Fireye2 – The Firestone Fireye2 is a little $99 USB DAC from the Netherlands. It has a nice full metal enclosure and has received some good reviews with the exception of some slight hiss and channel balance problems at low volume settings. But I didn’t see anywhere if it worked with the Windows volume control.
  • Leckerton UHA-4 (updated 3/2/2011) – The Leckerton UHA-4 is well over my budget at $169, but it’s small and also portable (it has a Li-Ion rechargeable battery). It has some appealing features including adjustable gain (see: Headphone Amp/DAC Gain), crossfeed, and Leckerton claims excellent channel balance tracking (to 0.1 dB) and impressive specs. The bad news is, according to Leckerton, it has a 10 ohm output impedance. That’s still unacceptably high for use with many balanced armature headphones.
  • NuForce uDAC2-hp – The $99 “hp” version of the DAC reviewed here supposedly uses the same problematic volume control as the original (1st generation) NuForce uDAC. The problems with the older volume control are well documented—i.e. uDAC2-hp Channel Balance.

WHY THE uDAC-2? So Goldilocks tried a few bowls of porridge, and considered several more, and as luck would have (or it turns out not), I finally chose the NuForce uDAC-2. A big reason was NuForce proudly claimed on their website:

As a step above the uDAC, the uDAC-2 boasts a highly linear TOCOS volume control for improved channel tracking at low listening levels in addition to 24bit/96kHz USB DAC and an improved headphone amp.”

The statement above led me to believe NuForce had fixed the often reported channel balance problem of the original uDAC (and the newer “hp”). The uDAC-2 specs on their website also looked good (but they have since revised them to be more realistic after our e-mail exchange—more on that later). And NuForce seemed like a good company. Unlike some boutique DAC manufactures, they have an office in the USA, a decent website, and people have said good things about their customer service. So I ordered one.

IT ARRIVES: The uDAC-2 arrived in a professional looking package and seemed nicely made with a solid metal enclosure and decent build quality. It’s really small—the footprint is smaller than a Sansa Fuze. It has a white LED power indicator, a volume control with on/off switch, and a 3.5mm headphone jack on the front. On the back is the USB jack, a coaxial digital output, and the L/R line out RCA jacks. It claims to support 24 bit formats and up to 96 Khz sampling rates. The volume control has a nice “silky” feel and it at least seems like a high quality product.

WINDOWS PLUG-N-PLAY: On both XP and Windows 7 PC the uDAC installed smoothly without needing any drivers. It shows up in Win7 as an “SPDIF Interface NuForce uDAC 2”. Apparently NuForce is using a CODEC chip, not a pure D/A chip, as Windows also think the uDAC-2 can record but it lacks any inputs to do so.

HISS & NOISE: First I checked for hiss with my sensitive Ultimate Ears SuperFi 5 Pro’s. There’s some slight hiss with the volume all the way down, and it increases a bit as you turn it up, but even at maximum volume it’s not very objectionable. It’s similar to the Sansa Clip+ and is quiet enough for me.

UH OH! In trying to listen to the line level outputs I discovered they’re disconnected when headphones are plugged in. But, and this isn’t good, the switches built into the jack that shut off the line outputs, caused one line level output to stop working sometimes even with the headphones unplugged. I had to insert and remove the headphone plug several times to bring the dead channel back to life. And with headphones plugged in, the line outputs are left floating which isn’t ideal either. This might cause hum or noise in some computer audio setups through the speakers when headphones are plugged in. If you’ll never use the line outputs, however, this isn’t an issue.

SUBJECTIVE LISTENING: Before measuring the uDAC-2, I listened to some favorite music with a variety of headphones and the line outs. It has enough power to drive all the headphones I tried to levels I’m happy with. I went back and forth a few times between the uDAC-2 and my Benchmark DAC1 Pre’s headphone output and didn’t notice any huge differences. But the Benchmark did seem to sound better. This could easily be subjective bias, however, as being much more expensive it’s hard not to expect the Benchmark to sound better. I did notice some channel balance problems. Perhaps the measurements would be more conclusive? Please also see the results of the public listening test.

udac-2-dscope-testTHE MEASUREMENTS: For the non-technical readers out there, the short version is I was really disappointed in the uDAC-2’s performance in several key areas. As mentioned at the start of this review, NuForce has confirmed my uDAC-2 is apparently OK and “within spec” for the first two problems. There are a total of four main problems and a few more minor ones I cover only in the tech section later:

PROBLEM 1: The uDAC-2 (like the original uDAC and uDAC2-hp) Has Serious Channel Balance Problems. Despite NuForce claiming to have upgraded to “a highly linear TOCOS volume control for improved channel tracking” the uDAC-2 still has what most would consider serious balance problems. Even set to nearly half volume (around 12 O’clock) it has a 1.4 dB error--anything greater than 1 dB is generally considered audible. At –30 dB it rises to a 3.3 dB error which is plainly audible. At –40 dB it’s a huge 10.3 db  error! You can easily hear the stereo image shift to one side as you lower the volume control. This isn’t a subtle problem. Anyone can hear it and, the more efficient your headphones are, the more it will be an issue as you’ll use the lower end of the volume range more. And it’s also present in the line outputs as they’re controlled by the same volume control.  It’s worth noting that channel tracking issues tend to be rather random. Every uDAC-2 will be at least a bit different.

The NuForce Response: Here’s NuForce’s reply to the channel balance problem after measuring their uDAC-2 sample (not mine):

“At 9 o'clock, there is hardly any signal, and analog pots do not behave well…

Volume at 9 o'clock (-41.6 db below reference): Balance Error: 8.8 dB
Volume at 10 o'clock (- 9.6 db below reference): Balance Error: 0.6 dB
Volume at 11 o'clock (reference level ~ 300 mV output): Balance Error: 1.0 dB

We consider this within spec.  I will emphasize again that listening test over and over again from so many people convinced us to adopt this current solution.  I understand that recording engineer might need a different product so I will post such details and plot online so that there is no mistaken about the intended customers.”

My View: I don’t agree that only “recording engineers” need decent channel balance—not if it’s a plainly audible problem. Someone with sensitive headphones studying in a quiet library, reading, etc. easily might end up with a big balance problem. And it’s also misleading to blame it all on “analog pots don’t behave well”. The circuit design has a lot to do with this issue, not just the potentiometer (volume control) used. I go into more detail in the technical section. NuForce says “so many people convinced us to adopt this current solution” but it seems more the opposite. If you look at all the uDAC reviews, the number one complaint is the channel balance problem. What “so many people” seem to want from NuForce is better channel balance!

A Useful Comparison: As proof this problem is easy to fix just look at the Behringer UCA202. It’s a $29 USB DAC and has a seriously cheap looking little thumbwheel for a volume control. The Behringer tracks within 1 dB over the entire range until –40 dB where it’s still within 1.5 dB. If Behringer can make a cheap volume control work well in their $29 USB DAC why is the $129 NuForce so much worse? My opinion, based on the NuForce response quoted above, is they think this level of error is perfectly OK. See the tech section below and my Behringer UCA202 Review for more details.

PROBLEM 2: The uDAC-2 Starts to “Clip” (badly distort) with a 0 dBFS signal(revised 3/3/11) - Using the line output, the NuForce has over FIFTY TIMES more distortion with a 0 dBFS input signal than a signal just 1 dB lower. With the headphone output it’s more than ten times higher. This matters because you only get a bit accurate full resolution stream with the PC’s volume control all the way up—see this Computer Audio Setup Guide for more details. And a lot of pop music is heavily compressed to make it sound louder with peaks frequently hitting 0 dBFS. Unfortunately, by NuForce’s own admission, the uDAC-2 “clips” 0 dBFS peaks. And it clips in this way at any setting of the volume control from the line or headphone outputs.

The NuForce Response: Here’s the NuForce reply after their own measurements on a different uDAC-2:

I confirmed that we did this so we can have more dynamic and useful volume for practical use, such as listening to music.    Our experience was that with MP3 or other format ripped music files, the output level could be very low, and there is not enough dynamic range. At the end of the day, customer buys the uDAC2 to listen with their ear, not their scope.

For testing, I said that by having -1.3dB, it will go below clipping.  In practice, there is no music recorded at 0dB. You are taking measurement at MAXIMUM digital volume. We maxed out exactly near 0dB, so the THD is around 1% as intended (hitting the voltage rail limit so that we have the loudest and un-distorted pracitical music playback. If we don't have 1% THD at 0dB, that means we are not fully using our voltage limit and we used 'less range' for music.

And customers can just slide the volume on their PC if they are playing such a track. There is no perfect optimization for such as entry level product (DAC1 cost almost 10X the price of uDAC-2 and it is linear powered with 30V for dynamics). But I think uDAC-2 is a better engineered product given the limitation (of USB powered device and cost).”

My View: The explanation above is based on the idea NuForce accepted some clipping to get a larger dynamic range. But this argument doesn’t make sense to me. If you reduce the level by even 1 dB the uDAC-2 no longer clips. So we’re talking about giving up only a trivial 1 dB of “range”! The uDAC-2 has about 94 dB of dynamic range. If they had designed it not to clip, it would have roughly 93 dB of dynamic range. That’s about a 1% improvement. Is 1000% (ten times) more distortion on peaks worth a 1% improvement in dynamic range?

Real World Music: (added 3/3/11) NuForce said above “In practice, there is no music recorded at 0dB”. This is simply false! If you pop a best selling Lady Gaga CD into the drive on your computer and click play, with the PC’s volume set to max so you get the full 16 bit digital resolution (an accurate bit stream), below is what gets sent to the uDAC-2. All those blue lines reaching “1.0” is where the signal is hitting, or getting very close to, 0 dBFS and hence would be much more seriously distorted by the uDAC-2 (click for larger). If you’re skeptical they’re really mastering CD’s this way, just download the free Audacity software and look at some for yourself:

Lady Gaga Just Dance Exactly As Ripped From The CD

Does NuForce Understand This Stuff? (revised 3/9) It’s my understanding the comments above are from the Vice President of R&D at NuForce who also claims to be an engineer. The stuff I’m measuring is audio engineering 101. So it’s hard for me, a fellow engineer, to understand why a company would knowingly trade 1% more dynamic range for 1000% more distortion. I personally think the comments from NuForce are more of a contrived excuse than a real explanation. I suspect this is a design error, or just sloppy engineering, and was not intentional. Just as with the Stereophile Review of their CDP-8 ,they likely never bothered to properly measure the uDAC-2 as, by their own admission, they prefer to “design by listening”.

I’m not aware of any rational reason for a DAC to clip 0 dBFS signals. And it’s not something I’ve ever seen in any other product. And their solution, lowering the PC’s volume, no longer delivers a bit accurate stream to the DAC—i.e. your ripped CD becomes “processed” by the PC’s operating system and is delivered to the DAC with less than the full 16 bits of digital resolution. I show a graphical representation of this in the tech section. The main reason most people buy stand-alone USB DAC’s is to get better performance, not worse, than what’s built into their PC.

Another Comparison: The Behringer UCA202, has virtually no distortion playing a 0 dBFS signal (< 0.008% THD+N). This is nearly 100 times better than the uDAC-2. And the noise of the UCA202 is only 2 dB worse (-92 db vs –94 db). So, as with the channel balance, Behringer manages to do a much better job with a much cheaper product.

PROBLEM 3: High Output Impedance. I didn’t bring this up in my emails to NuForce, but apparently that “improved headphone amp” NuForce claims on their web site (see quote above) doesn’t include having a sufficiently low output impedance. The uDAC-2 measures about 6 ohms and this is well above the 2 ohms I consider acceptable for use with typical Balanced Armature headphones. Even the lowly $29 Sansa Clip+ and $20 FiiO E5 portable amp have much lower output impedance. I explain why this matters in my Amp Impedance article, but all you have to do is look at the frequency response below in blue:

NuForce uDAC-2 -3 dBFS Swept Frequency 15 Ohms (yellow) UE SuperFi 5's (blue) (Ref ~400 mV)

In the graph, the popular Ultimate Ears SuperFi headphones cause over 4 dB of frequency response deviation with the uDAC-2. While the flat yellow line across the middle is essentially what you’d get if it had a much lower output impedance. Most would consider the blue response to be readily audible—especially as, in this case, it’s worst at midrange frequencies where the ear is most sensitive. With the uDAC-2 the frequency response will change in unpredictable ways--the above is just one example--with different headphones.

PROBLEM 4: Too Much Maximum Gain. I also didn’t bring this up to NuForce, but one can argue the uDAC-2 has too much maximum gain or should have adjustable gain. The measurements show with most any load, it clips above about 1 O’Clock on the volume control. Even the line outputs clip. This means the entire upper range of the volume is control is wasted when listening to most music sources. And given its high output, few headphone users will ever go above 11 or 12 O’Clock. This makes the channel balance problem even worse as it forces most people to use the lower part of the volume range. It may also make noise problems worse as I explain here. A partial solution is to reduce the volume in Windows, but, just like with the clipping issue, this means reducing 16 bit CD quality music to less than 16 bits of resolution. The only reason I know of to have a product designed this way is for the rare use where someone has seriously inefficient headphones and is also listening to an improperly ripped track recorded at a much lower than normal level. Why design a product to work for 1% of the users at the expense of the other 99%? See the technical section below for more details and graphical examples.

THE OTHER MEASUREMENTS: In most other ways the uDAC-2 measured similar to, or in some cases much worse than, the vastly cheaper Behringer. It did much worse, for example, with high frequency distortion and jitter. See the technical section for more details.

WHAT DOES THIS SAY ABOUT NuFORCE? This is a really good question. Before I tested the uDAC-2, and received NuForce’s responses quoted above, I respected the company. They have some happy customers, they’re responsive to problems, have a good refund policy etc. So, in some ways, they seem like a respectable business. They also seemed to take my concerns seriously and were very prompt in their response.

But it’s hard for me to accept a company shipping a $129 product with the sort of flaws the uDAC-2 has. It’s even harder for me to understand with a second generation product like the uDAC-2. NuForce already knew about the channel balance problem with their original uDAC and claims they fixed (or at least seriously improved) the problem. But did they? Given how much better the first generation (now many years old) Behringer USB DAC measures even using much older technology, and at a much lower price, it’s especially hard for me to forgive the uDAC-2’s poor measurements.

DID NuFORCE EVEN KNOW? (revised 3/9) After they received my measurements, NuForce didn’t seem to even know what the typical performance of the uDAC-2 should be. This was especially a surprise considering the VP of R&D, also an engineer, was apparently one of the two employees corresponding with me. Shouldn’t he already be familiar with the uDAC-2’s performance? It’s not like NuForce is a huge company or has lots of products. But, instead of knowing if my results were reasonable, or not, NuForce had to go borrow another company’s Audio Precision analyzer to measure their own product. And only then could they tell me if what I measured was normal. That just doesn’t make sense to me unless they really had no idea of what the real world performance was? This is also consistent with what happened with the Stereophile Test of the CDP-8 last year. NuForce admitted to being “surprised” as they apparently had not made similar measurements to Stereophile’s standard set of tests.

PRODUCT MANAGEMENT 101: Based on the above, I have to wonder, did anyone at NuForce properly measure the production version of the uDAC-2 before initially shipping it? Did they check to make sure they really had solved the channel balance problem? Did they verify the basic performance specs? Did they set up quality control standards to make sure the production units are within spec? Do they hold the factory to documented specifications? If the answer to any of these questions is “yes”, I would expect them to have already known what is “within spec” and answer my questions without needing to go out and take measurements. But, in this case, even the VP of R&D apparently didn’t know or have access to that sort of common information. Does that seem weird to anyone else? And if they didn’t know, where did the specs on their website come from?

MARKETING HYPE: (revised 3/9) Besides the claim of a new “highly linear” volume control with “improved tracking”, other NuForce specs influenced my decision to buy one. For example, up until a few days before publishing this review, NuForce listed on their website:

  • Dynamic Range 110 dB
  • THD+N = – 95 db

If you convert –95 dB to a percentage, it’s 0.0018 % THD+N. NuForce, since our email exchange, has removed this spec from their website and now just lists “0.05%” instead—which is a much more mediocre but realistic –66 dB. They also lowered the dynamic range from 110 dB to only 90 dB. These are huge changes in specs. The previous specs were impressive audiophile-grade numbers. The new specs are similar to the sound hardware built into many PCs. I have screenshots of the old web page for anyone interested in their changes. Don’t you think a company should base their published specs on some actual measurements? Apparently NuForce did not. Or perhaps they intentionally wanted the uDAC-2 specs to appear better than they really are?

WHAT ABOUT OTHER NuFORCE PRODUCTS? Have they used similar “tuning” and compromises in their other designs? Do their more expensive products have similar measured or performance issues or not meet their published specifications? Do they all have 6 ohm output impedances? I really don’t know but I do wonder.

BOUTIQUE AUDIOPHILE COMPANIES: To be fair, NuForce isn’t alone. There are plenty of small “boutique” audiophile companies that found a market niche selling poorly engineered, or what many would consider marginal performing, products. Nearly all of them, when someone challenges the performance, respond with excuses including some version of NuForce’s “At the end of the day, customer buys the uDAC2 to listen with their ear, not their scope”—i.e. that specs and performance don’t matter and it’s better to "design by ear”. And there’s often at least the implication, and sometimes the direct claim, that better measured performance would somehow sound worse. This is not true. Look at the Benchmark DAC1. It has among among the best measurements of any audio DAC anywhere. And it’s also been rave reviewed by some of the most critical, high-end, audiophiles writing for the uber-esoteric audiophile media. And if you don’t like that example, just look at how the Behringer USB DAC performs. It’s entirely possible to design gear that measures well, sounds great, is reasonably priced, and doesn’t require the manufacture to make any excuses. Behringer is just one example. There are many others.

WHAT ABOUT THE POSITIVE uDAC-2 REVIEWS (added 3/2/11)? The channel balance issue will literally be random from sample to sample of the uDAC-2. If the potentiometers NuForce is using are not individually tested, then you could end up with one that tracks fairly well or one that’s really poor. So some of the good reviews you read might be from those who got lucky. And if someone is already lowering the volume on the PC side they are less likely to use the lowest range of the uDAC-2’s volume control where the tracking is worst. The same is true if they have really power hungry low sensitivity headphones.

The 0 dBFS distortion issue only shows up on certain music and with the PC volume set for a bit accurate stream. It’s also possible it may vary from sample-to-sample due to component tolerances. The output impedance interaction is very headphone specific. With some headphones it may be minimal or tweak the frequency response in ways someone actually prefers. While with other headphones it may cause more severe variations of the sort that don’t usually sound good (like the big midrange boost and HF cut with my SuperFi 5’s). The excessive gain issue, again, can be partly overcome by turning down the volume on the PC side and depends on the headphones used. So it’s easy to see how some people wouldn’t care as much about the problems I’ve found. But, to me, that doesn’t excuse the glaring flaws when they’re so easily corrected.

THE PSYCHOLOGICAL ASPECT: How psychological and emotional aspects influence what we hear is well documented. For one good reference, see Dishonesty of Listening Tests. Humans, even if they’re not aware of it, are very influenced by expectations, the comments of others, the money they spent, the physical look and feel of a product (and here the uDAC-2 does well), the brand name, and other factors. For example, the Behringer A500 amplifier was widely criticized as being a “cheap clone” and sounding awful. It was indeed very cheap. But in an interesting blind test, serious audiophiles couldn’t tell it from a much more expensive audiophile amp. Virtually all of the uDAC-2 reviews and forum posts I’ve seen have been conventional “sighted” listening and hence are subject to this same well documented bias. You can draw your own conclusions but I’d encourage everyone to follow the two links if you haven’t already. They might help you save lots of money :)

BETTER ALTERNATIVES TO THE uDAC-2 (revised 5/2): As of May 2nd, I’ve now tested the FiiO E7 and can safely say it easily outperforms the uDAC-2 in nearly every area and represents a much better choice and value. I’d still like to get my hands on the Firestone Fireye2 as, based on this review and other information I’ve seen, it may offer better performance than the uDAC-2, at a lower price, with fewer problems. If you only need line outputs (no headphone jack), the similarly priced HRT Music Streamer II is worth a look.

BOTTOM LINE: To conclude the less technical part of this review, I believe the uDAC-2 has some inexcusable flaws. How much some of these problems are actually audible is open to debate. But, given nearly all the problems could have easily been fixed, I think it’s hard to defend the problems in a supposedly “audiophile” DAC selling for $129 from a company that specializes in DACs. NuForce argues their design is “better engineered”, but when a $29 Behringer DAC outperforms it in nearly every area, I have a hard time accepting that. Personally, I don’t see any reason to buy a uDAC-2 given its flaws and I’m going to return mine for a refund. But, ultimately, everyone has to decide what’s best for them.


udac2-uca202-transit-0202-HD590TECH INTRO: With the drama out of the way, I’ll try to focus on the detailed results. A few are perfectly fine, a few are questionable, and some are the worst I’ve ever seen. For more details on how I measure, and the equipment I use, see my Testing Methods.

THD AT 0 dBFS: I run this same test on every digital device I test. It’s the standard “reference” used in most digital audio testing to compare other levels and measurements to. Here’s the uDAC-2 via the headphone output with a 15 ohm resistive load:

NuForce uDAC-2 44.1 Khz USB 1 Khz 0 dBFS 15 Ohms Reference Level 400 mV (volume 12 O'clock)

The high distortion here is from the analog side of the DAC stage clipping (hitting the supply “rails”) with a 0 dBFS signal. The spectral “signature” of clipping is having higher odd order harmonic distortion than even order harmonics. And if you look at the circled spectrum above, you’ll see exactly that. Odd order harmonics are widely considered to be far more unpleasant, and hence more audible. In this case they’re about –48 dB below the signal. Remember cassette tape hiss? That was generally much quieter--around 65 dB below the signal. So we’re talking about “unpleasant audio garbage” that’s a whopping 17 dB louder than typical tape hiss. Some might argue this level of distortion could be audible under some conditions. It’s important to note this happens at any setting of the NuForce’s volume control with any load. As explained earlier, I believe it’s a design flaw. Here’s the same test on the line outputs at 1 volt RMS into 100K:

NuForce uDAC-2 44.1 Khz USB 1 Khz -0 dBFS Line Out 100K Reference 1 V RMS)

If we drop the level by even a barely audible 1 dB, here’s what happens to the distortion of the Line Outputs:

NuForce uDAC-2 44.1 Khz USB 1 Khz -1 dBFS Line Out 100K (Ref 1 volt)

Same thing on the headphone output (but the uDAC-2 headphone amp has about five times higher distortion in general):

NuForce uDAC-2 44.1 Khz USB 1 Khz -1 dBFS 15 Ohms (Ref ~400 mV)

The huge drop in distortion is because the DAC circuit is no longer running into the power supply rails (clipping). For reference, here the $29 Behringer reproducing the exact same 0 dBFS test signal that gives the NuForce fits on the exact same Line Out dScope test:

Behringer UCA202 1 Khz 0 dBFS 44.1 Khz USB Line Out 100K with comments

Note with the Behringer the more pleasant sounding 2nd harmonic is way down at –82 dB and the unpleasant 3rd harmonic is at –100 dB which just about everyone will tell you is inaudible. The rest of the harmonics are essentially lost in the noise floor. Compare this to the “forest” of distortion products of the NuForce at 0 dBFS above (The odd ultrasonic “bump” in the Behringer spectrum is above the audible range and explained in the UCA202 Review.)

NOISE LEVELS: Here’s the headphone noise under the same conditions as above but with a barely visible –115 dBFS signal to give the DAC something to do (many DACs mute and shut off with no signal giving an unrealistic noise measurement and making the specs look better—but no cheating allowed here):

NuForce uDAC-2 -115 dBFS Noise Performance 15 Ohms (ref ~400 mV)

Here’s the same measurement via the Line Outputs. This is good noise performance—especially for a USB powered device. It’s about 2 dB better then the Behringer UCA202. This agrees with my subjective review of the noise earlier":

NuForce uDAC-2 -115 dBFS Noise Performance Line Out 100K (Ref 1 volt)

MAXIMUM OUTPUT: Into a 15 ohm load, here’s the impressive maximum headphone output into 15 ohms just under 1 % THD+N:

NuForce uDAC-2 1 Khz 0 dBFS Max Output Under 1% THD N 15 Ohms Volume 1 O'Clock

Here’s the same thing into 150 ohms to better approximate higher impedance headphones:

NuForce uDAC-2 1 Khz 0 dBFS Max Output Under 1% THD N 150 Ohms Volume 2 O'Clock

This is very respectable output. Into 15 ohms it’s 47 mW and into 150 ohms it’s 32 mW. The uDAC-2 should drive most any headphone plenty loud.

GAIN AND VOLUME CONTROL: In the last two graphs, note the NuForce has reached max output at between 1 O’Clock and 2 O’Clock on the volume control. This means listening to typical material with any headphones, or the line outputs, the entire upper range of the volume control is wasted (assuming you send the full 16 bit accurate signal to the DAC from the PC). And 30 – 50 mW is more power than most can safely use with typical headphones. So, as a result, few users will likely get past half volume and the entire upper half of the volume control’s range will be unused unless they turn down the volume in the PC’s mixer. But this will reduce their CD quality audio stream to less than 16 bit resolution. Here’s the NuForce with a –10 dBFS signal (so it won’t clip at full volume) at exactly half volume (12 O’Clock) which is about as loud as most will ever use (~20 mW into 16 ohms at 0 dBFS):

NuForce uDAC-2 -10 dBFS 15 Ohms Headphones Reference at Exactly 12 O' Clock Volume (189 mV)

Leaving everything the same, with the volume all the way up to max at 5 O’Clock:

NuForce uDAC-2 -10 dBFS 15 Ohms Headphones Reference at Max Volume (Ref 189 mV)

So there’s at least 10.6 dB of “wasted gain” for most users. So to use the full range of the NuForce volume control, you have to turn the volume in Windows down by 10.6 dB. Here’s the PC’s output to the DAC at full volume with peaks hitting 0 dBFS:

Bitstream to DAC with PC at Max Volume

And here’s what it looks like if you lower the PC’s volume slider by 10.6 dB to correct for the NuForce having too much gain:

Bitstream to DAC with PC at -10.6 dB Volume

Now only about 25% of the digital (numeric) dynamic range is being utilized. The other 75% of possible bit values are completely unused. Some may argue over how audible this is, but it’s clearly a compromise. If the uDAC-2 had less overall gain, or even better adjustable gain like Leckerton, Firestone, and others offer, it wouldn’t be as compromised.

HEADPHONE OUTPUT IMPEDANCE: Here’s the No Load output referenced to the same 400 mV at 15 ohms level used earlier. The voltage rises to 561 mV with no load. If you do the math, this is a 6 ohm output impedance:

NuForce uDAC-2 44.1 Khz USB 1 Khz 0 dBFS No Load (for output impedance - Ref ~400 mV)

WHY IMPEDANCE MATTERS: Here’s the same graph from earlier, the frequency response with a 15 ohm resistive load vs the Ultimate Ear SuperFi 5 Pro’s on the uDAC-2:

NuForce uDAC-2 -3 dBFS Swept Frequency 15 Ohms (yellow) UE SuperFi 5's (blue) (Ref ~400 mV)

THD vs FREQUENCY: I could have run this test at 0 dBFS where the NuForce would have had a miserable result. But, to be fair, I ran it at –3 dBFS where the uDAC-2 has about 0.05% THD+N at 1 Khz. Here’s the sweep (in blue) plotted on the same graph as the Behringer UCA202 (shown in red):

Behringer UCA202 (red) vs NuForce uDAC-2 (blue) Swept THD N -3 dBFS 44.1 Khz (ref ~400 mV)

You can see above 500 hz the uDAC-2’s distortion heads skyward. The Behringer does far better here. This implies poor design (or odd design trade-offs) in either the DAC implementation, low-pass (“reconstruction”) filters and/or the headphone amplifier.

IMD DISTORTION: Here’s the SMPTE plot at –2 dBFS which is just below the clipping value of the combined SMPTE IMD test signals (60 hz and 7 Khz in a 4:1 ratio):

NuForce uDAC-2 SMPTE IMD -2 dBFS 15 Ohms (ref ~400 mV)

Here the DAC is likely starting to clip at –2 dBFS, just as it does with a single tone near 0 dBFS. See the “mountain” around the base of the 7 Khz signal? Here’s a closeup:

NuForce uDAC-2 SMPTE IMD -2 dBFS Zoom 7 Khz 15 Ohms (ref ~400 mV)

All those spikes spaced multiples of 60 hz apart are IMD—that’s the 60 hz signal interacting with the 7 Khz signal in undesirable ways. Here’s the lowly Behringer with the exact same –2 dBFS signal and test. Check out the almost completely clean noise floor with only a few spikes that barely make it to –100 dB:

Behringer UCA202 -2 dBFS 44.1 Khz USB Dual Tone SMPTE IMD Spectrum Closeup 7 Khz

WHY THIS MATTERS: The clipping point of an amplifier isn’t determined by the level of any single frequency. It’s the combined level of all frequencies. With the NuForce, even though both tones individually are well under the clipping point, the combined result pushes the compromised DAC design into far more distortion than the Behringer even though it technically shouldn’t be clipping. The IMD test better approximates the complex interaction in real music.

FREQUENCY RESPONSE: With a purely resistive load of 15 ohms, the only interesting thing here is the channel balance problem (blue is left, yellow is right). Otherwise the uDAC-2 has sufficiently flat frequency response:

NuForce uDAC-2 Freq Sweep 10 hz 20 Khz -3 dBFS Ch A (blue) Ch B (yellow) 15 Ohms (ref ~400 mV)

However, as previously shown, the uDAC-2 doesn’t do nearly as well with a real world load like the Ultimate Ear SuperFi 5 Pro’s headphones:

NuForce uDAC-2 -3 dBFS Swept Frequency 15 Ohms (yellow) UE SuperFi 5's (blue) (Ref ~400 mV)

DAC Linearity: As mentioned in the Sansa Clip+ Review, this can be a good indicator of the quality of the DAC chip and here the NuForce does well rendering the –90 dBFS signal at –90.2 dB. At this low level, all the distortion is hidden in the noise.

NuForce uDAC-2 -90 dBFS DAC Linearity 15 Ohms (ref ~400 mV)

JITTER SPECTRUM & PITCH ACCURACY: Another key difference between DACs, and especially USB DACs, is their jitter performance. There’s a lot of debate about this topic, but I can personally attest to having heard plainly audible jitter in a listening test. So don’t let anyone tell you it’s always inaudible. You can read more about it, and how it’s typically measured, in my Jitter Post. The USB interface and clock design can really make a significant difference. Here’s the Nuforce running my standard jitter test:

NuForce uDAC-2 11025 hz -6 dBFS Jitter Spectrum 15 Ohms (Ref 400 mV)

And, for comparison, here’s the Behringer:

Behringer UCA202 11025 hz -6 dBFS 44.1 Khz 150 Ohms Jitter Spectrum (ref ~400mV) with comments

There are some interesting differences here. The Behringer’s jitter side bands are at about –120 dB while the ones on the NuForce are some 15 dB higher at –105 dB. This is a substantial difference. Also notice the much wider “spread” at the base of the signal. This is generally an indicator of very low frequency jitter (which some argue is the more audible variety) and the uDAC-2 has quite a bit of spread which isn’t a good sign. In fact it may have the worst jitter performance I’ve ever seen since I started doing this test. I can’t say with any certainty if the uDAC-2’s jitter is readily audible, but I can say it’s a lot worse than even the much cheaper Behringer. At least the pitch is OK-but it almost always is.

SQUARE WAVE TEST: Not much exciting here, the NuForce does fine:

NuForce uDAC-2 1 Khz -3 dBFS Square Wave

CHANNEL SEPARATION: Here the NuForce is average at about 47 dB and flat with frequency (which isn’t a problem):

NuForce uDAC-2 0 dBFS Swept Channel Separation (ref ~400 mV)

Here’s the cheaper Behringer, once again performing much better, for comparison (although the 150 ohm load gives it an advantage):

Behringer UCA202 Channel Separation vs Frequency 150 Ohms (ref ~400 mV)

CHANNEL BALANCE: If you scroll way back, you’ll see the channel balance error was 0.55 dB at the reference level of 400 mV. Turning down the volume down just 3.5 db from there (a typical moderately loud listening level), you get an audible 1.4 dB of balance error—not good:

NuForce uDAC-2 44.1 Khz USB 1 Khz 0 dBFS 15 Ohms Channel Balance Volume -3.5 dB (Ref ~400 mV)

What happens at –20 dB? It’s a still (barely) audible 1.2 dB:

NuForce uDAC-2 44.1 Khz USB 1 Khz 0 dBFS 15 Ohms Channel Balance Volume -20 dB (Ref ~400 mV)

Next is –30 dB which a person might use say studying in a library with sensitive headphones. Here it’s a very audible 3.3 dB error:

NuForce uDAC-2 44.1 Khz USB 1 Khz 0 dBFS 15 Ohms Channel Balance Volume -30 dB (Ref ~400 mV)

And, at –40 dB which is about as low as anyone is likely to listen at, the error is a huge 10.3 dB:

NuForce uDAC-2 44.1 Khz USB 1 Khz 0 dBFS 15 Ohms Channel Balance Volume -40 dB (Ref ~400 mV)

The above is the worst channel balance I’ve ever seen in any product by a wide margin. And it’s worth noting, at a similar control position (about 9 O’Clock), even NuForce measured a very poor 8.8 dB on their uDAC-2 sample and considered it “within spec”. This is an avoidable problem even with a really cheap volume pot. Behringer’s “thumbwheel” volume control probably costs them about $0.15 but it performs much better. This is likely due to more careful engineering and a better circuit design.  At –40 dB the Behringer has only about 1.5 dB of error and it’s below 1 dB (inaudible) at all settings above that. If Behringer can do so much better in a much cheaper product, what’s NuForce’s excuse?

MEASUREMENT SUMMARY: I’ve hopefully written enough about the numbers. I personally think these measurements, and NuForce’s response, call into question the integrity of the product and their overall design philosophy. But you can form your own conclusions.

SUBJECTIVE vs OBJECTIVE CORRELATION: (added 3/3/11) When I originally, before doing any measurements, compared the uDAC-2 to the Benchmark DAC1 I thought I heard differences. And I believe those differences may correlate with one or more of the following measurements:

  • The most likely thing I heard is the 4+ dB frequency response deviation with my SuperFi headphones. The midrange is broadly boosted and the treble is sharply cut in a narrow notch. If you’ve ever played with a notch or other steep slope equalizer/filter you know you get a very odd audible effect when you sharply cut a narrow range of frequencies. It can sound like the music is playing through a plastic tube. I think I heard a hint of that combined with a slightly glaring “in your face” midrange boost.
  • I also heard some image shift--even if it’s only a few dB at the volume setting I was using. This is especially obvious when you’re switching back and forth relatively quickly. The SuperFi’s are very efficient so the volume control was set fairly low where the tracking is worse. This is no surprise given the very poor channel balance measurements.
  • I also may have heard some increased distortion on peaks making loud passages sound more “gritty'” or “dirty”. This is because the uDAC-2 clips the peaks with distortion products as high as –48 dB which is easily audible by itself. The only question is if it’s fully masked by the music.
  • I may have also heard some audible effects from the uDAC-2’s unusually high levels of jitter (among the worst I’ve ever seen).
  • See also the results of the public listening test.

NOTES TO NuFORCE: (revised 3/9) In the interest of constructive criticism, and having a better product available, if I were designing a “uDAC-3”, I’d make the following changes:

  • Fix the DAC circuit so it doesn’t clip at 0 dBFS. This shouldn’t be hard to do as every other DAC and digital player I’ve measured over many years can handle a 0 dBFS input signal without a problem.  It’s probably a gain error or something similar?
  • Use a better volume circuit so errors in the potentiometer are not made much worse by the respective ratios of the voltage divider, input impedances, etc. And sourcing a better pot wouldn’t hurt either.
  • Lower the output impedance to around 1 ohm or less. This might be as simple as a resistor change. If the amp isn’t stable (or able to withstand a short circuit) without 6 ohms of series resistance, correct the feedback loops and/or use a better IC/design. You could even just copy the amp circuit in the $20 FiiO E5 which has a near zero output impedance.
  • Reduce the overall gain by around 5 or 6 dB to provide a better match for most uses and headphones. This will help volume tracking and lower the noise floor in some circumstances. It will also make volume adjustments less “touchy”. Even better would be a choice of gain with a jumper or switch like some of your competitors have. Or perhaps offer two versions: A low gain and high gain model with different internal component values. Lowering the gain will do more to improve the noise performance than clipping 0 dBFS signals ever can. 
  • Find out what’s causing the excessive high frequency distortion and reduce it to more typical levels.
  • Don’t route the line output through cheap switch contacts in the headphone jack that are apparently prone to problems (and/or contamination from the PCB wash process). If you still want to switch the line outputs, don’t leave them floating when headphones are plugged in and find a better way to do it.
  • Establish a full set of performance specifications based on properly measuring the final prototypes and make sure the contract manufacture is required to perform testing and meet the same specifications. This will prevent being “surprised” when Stereophile, or people like me test your products.
  • Publish the above specifications on your website with reasonable confidence the product the customers receive will actually meet them instead of specifications that seem to have no basis in reality.

IF YOU ALREADY OWN A uDAC-2: I’d suggest accepting the lesser of evils and dropping the volume on your PC a bit to help with some of the problems. You’re still stuck with the high headphone output impedance causing frequency response problems, high levels of jitter, and excessive high frequency distortion, but at least it won’t clip and you can use more of the uDAC-2’s volume control’s range to lessen the channel balance problem.


  1. Thankyou. You very clearly explained how and why this product is flawed and included Nuforce's respones. The sometimes surreal audiophile world needs more unbiased reviews with accurate and correctly interpreted measurements. More please!

  2. This blog is quickly becoming a great resource. Despite being such a subjectively influenced area, the audiophile community should demand more of this type of objective technical review. Your comments are insightful enough to make even the technical section understandable without a degree in audio engineering.

    I'm in the market for a USB DAC and was previously set on the uDAC-2. Good price and feature set, good reviews, seriously alluring looks... but apparently, crap internals and SQ. Thanks for changing my mind.

    The Behringer UCA202 is tempting at it's ridiculously affordable price, but I have a pair of relatively low-impedance IEMs (43 ohm) I'd like to drive as well as my speaker amp. If you come across a low output impedance DAC with RCA/coax outputs, let us know.

  3. I wonder why most of these models do not have a Line-Out. Don't you headphone people use speakers also? =P

  4. Yes, that's a trade-off with the Leckerton for example. You can always use a headphone output as line out (most have plenty of signal for that) but the reverse is not true. The fact is it's the headphone output of a lot of equipment that's most in need of performance improvements--like with my HP TouchSmart PC. If someone only needs line out, the similarly priced HRT Music Streamer II appears much better engineered than the uDAC-2.

  5. Ok, I just got a response from Leckerton. Both their UHA-4 and UHA-6 have a 10 ohm output impedance, so most people can cross those off their shopping list if you have balanced armature IEMs or any other headphone with significant impedance variations.

  6. How come Sandisk can do it on the Clip+, but these companies can't on their $100+ products?

    I don't get it...?

    Is there any advantage in having a higher output impedance at all?

  7. That's a good question Vittau. I don't have the review up here yet, and it has it's own "fatal flaw", but even the $20 FiiO E5 portable headphone amp has a near zero output impedance. I'm not aware of any advantage to higher output impedance unless the headphones were specifically designed for it--but even then the design impedance would rarely match the output impedance, so what's the point? I suspect it's most often done because it makes the device/amp/DAC cheaper to manufacture and easier to design for various technical reasons.

  8. This blog is just what the doctor ordered. Please keep posting. :) Also, get a Paypal donation button, for heaven's sake.

  9. I have a uDAC-2 with a pair of JVC HARX900 headphones I use with my computer setup. What you recommend I do?

  10. At least Nuforce admitted that they know about these problems. Still it seems like they are making excuses for relatively cheap fixes.

  11. Please see the response we posted on this thread: http://www.head-fi.org/forum/thread/542281/nuforce-udac-2-drama-detailed-measurements#post_7314785


  12. This comment has been removed by a blog administrator.

  13. Just so everyone knows, I deleted two posts here of a sales nature from NuForce. This is a non-commercial blog. And I'm OK with anyone, even manufactures, discussing technical issues, here. But I'm not OK with NuForce, or any other company, marketing promotions for their products here. Anyone can go to the NuForce website if they want sales and marketing information from NuForce. I provided a link in my review.

  14. Stereophile noted that the $1500 NuForce CD player had some terrible measurements. Mr. Lim's response there was that the company had failed to actually check its measurements. While failing to know the measurements of its own $130 Udac seems at the very least bad form, exercising the same poor engineering and quality control in a $1500 CDP seems outrageous to me.

    I'm providing a link to that review's measurements section ( be sure to read through to the end). If this link isn't acceptable, please remove.



  15. Thank you very much Mainelli for the links to the Stereophile review. I have updated my article above to include the information. I didn't realize this isn't the first time NuForce has been "surprised" by poor third party measurements of their products.

    Just like they have done here, NuForce justified the poor performance by saying they essentially designed the product by ear, and it sounded good to them, so why bother to measure it? I'm glad Boeing doesn't build airplanes that way--just skip all that silly FAA required testing as long as it "feels good" to the pilot.

  16. it would be nice if you could build and review an amb.org gamma 1 DAC, as I love a bit of DIY and as an AIS (audio idiot savant) I am under the impression a DAC will give better sound on my sr80 and sr225,

    thanks for the hard work ;)

  17. @Rahil, Thanks. I have a lot of respect for the concept behind AMB but their designs could benefit from some better test methods. So perhaps that's something I may be able to help with in the future.

    As for "impressions of better sound" don't believe all the subjective reports you read. Nearly all are from sighted listening tests and highly biased. And when it comes to headphones, due to output impedance interaction, it makes it really hard to make valid comparisons.

    For example, someone might like how a certain DAC makes their Grado's sound. They might like the sort of boomy exaggerated bass you get with a high output impedance DAC. Someone else might like the tighter, deeper bass of the Grado's on a DAC with a lower output impedance. It's very subjective and comes down to the reviewer's tastes, musical preferences, and that exact pairing of a particular source with their particular headphones.

    They were not rigorous, buy my two listening challenges here seem to demonstrate differences between DACs are smaller than most think. Roughly half the listeners couldn't hear any differences even comparing a $30 DAC to a $1600 one.

    Some DAC's intentionally alter the sound in various ways and do indeed sound different. But if you're looking for accuracy, transparency and sound that's true to the source, you don't need an exotic DAC to get that. For example, the listeners who did hear a difference voted the $30 Behringer DAC sounds better with headphones than the $130 NuForce. And the Behringer also measures better in most respects.

  18. Great article, thanks. It reminded me of this one.


  19. Thanks for the above link on the NuForce Reference 8 ($1600 per stereo pair). To summarize Sander Sassen's review, the measured results were "disappointing" and "a genuine concern". And when listening subjectively he was "utterly disappointed". Ouch.

    Again quoting Sassen: "Their design includes a direct copy of the known-bad standard HIP4080 MOSFET driver application circuit (including its infamous lack of EMI control), their incorrect use of feedback, the excessive RF output and abysmal performance goes to show that they still have a lot to learn about designing and building class-D amplifiers."

    As someone else pointed out in the Listening Challenge Results comments, NuForce seems to get a lot of their products wrong. Sometimes they try to fix them when they get "caught" and sometimes (as with the uDAC-2) they just argue they're poorly designed on purpose.

    There's a consistent trend of complaints, poor measurements and poor reviews. In doing some research the NuForce Icon Mobile has received many negative reviews and was even called "worthless". Someone else pointed out the NuForce Icon desktop amp has audible high frequency noise when used with efficient speakers. And, of course, Stereophile was less than impressed with the $1500 CDP-8.

    Perhaps I should start a dedicated article that tracks and documents NuForce's many negative reviews and product flaws?

  20. +1 for the dedicated thread. sounds like this company is *.

  21. Le sigh! As someone who just took delivery on a uDac2, this is depressing news indeed. Worse, it sounds FINE to me, and I really like the form factor and finish.

    I nearly purchased a Behringer 202, but read a few reviews referring to the amp and headphone jack as "worse than onboard audio". At under $30, I decided that it had to be a case of the product being too good to be true.

    To find out now that I could have had a better product, with more features, at less than 1/4 the price is rough.

  22. Hey, if your uDac-2 sounds fine to you, and you don't notice the channel balance problems, keep it. Just drop the level either in your source application or the PC's mixer by a dB or two and you won't experience the clipping problem. Or, if you do notice balance or output impedance related problems, return it while you still can.

    The Behringer UCA202 also has serious issues as a headphone DAC. And even via the line outs the uDAC-2 is better in a few areas. So it's not a direct replacements for the uDAC-2.

    I'm hoping to measure a FiiO E7 soon. It's direct competition to the uDAC-2. So that should prove interesting!

  23. Hey NwAvGuy, thanks for the speedy feedback. I'm Anonymous from above. Before finding this page I hadn't seen any reviews of these low-cost Dacs by anyone who understood the engineering of the things. I narrowed down the selection by price range, then reviews, then features, and finally went with the most handsome package that seemed to be a convergence of all three. I read comparisons favoring the uDAC over the E7, then sec appeal took over and I decided I didn't need a battery or a Dac that looks like an off-brand Mp3 player. The analog knob, solid build and barebones simplicity won me over for Nuforce.

    I had bought it primarily for my Beyerdynamic DT770 Pro-80 at work, with which I hadn't noticed any volume issues. Brought it home tonight to use with my 32-ohm Grados and lo and behold, audible pot balance issues in the lowest 10% of the range. This is disappointing, but I'm glad I found out before the 30-day guarantee ran out.

    I guess what I want to know now is: in your well-informed opinion, is there a product in the same price range or below that produces a cleaner signal while still having a) portability and b) the balls to deliver big sound through 80- ohm bass-heavy Beyers?

    Is the Behringer a better choice as compact dedicated headphone Dac/amp for all-day listening?

  24. Given what you've said, I wouldn't buy the Behringer. The E7, lack of the PC volume control aside, is hopefully going to outperform both the Behringer and uDAC-2 on my test bench. It should measure at least as well as their much cheaper but still impressive E5. If you're willing to consider the Behringer you should really think more about the E7. Here's a good review:


    Otherwise, you can either live with the balance issues with the uDAC-2 and your Grados, or consider something else like the Leckerton UHA-4. Supposedly they have fixed their output impedance issue but, like the E7, I haven't tested one yet. Another option is Firestone. There's a link to a review in my article above.

    If you haven't already, The Well Tempered Computer site (link above in the right column) has links to lots of DACs. But most are not headphone DACs and are more expensive.

    It's really frustrating NuForce didn't do a better job with the uDAC-2. As you said, it's otherwise a solid product for applications like yours (and mine).

    How do you like the closed back DT770-80's for long term comfort and sound quality? My Denon D2000's are the best closed back headphones I've found yet but I haven't tried the DT770's.

  25. I haven't ever tried any Denon headphones, so I can't do a comparison. Beyerdynamic's whole line of headphones through the 7xx, 8xx and 9xx are amazingly comfortable. They're built on big round pillows, covered in soft velour. I (and a lot of people, apparently) don't think headphones get any more comfortable or sturdy than a set of full-sized Beyers.

    The unamped sound I would describe as flat, bordering on dark. Not as dark as the Sennheiser HD280-Pro, but dark in its own right. It sounds better than the Senns, and comfort is in another league entirely (as the Senns clamp onto my jaw muscles like a pit bull). My girlfriend, the owner of said Senns, can't even use them for recording because she's a singer and they make her jaw hurt too much to perform.

    The Beyers aren't the most "closed" of closed headphones, but I think the lack of excessive clamping force makes them more comfortable for all-day wear. They are quiet enough that ambient office noise doesn't stand out while listening to music, and the only comfort issue I notice is that they get really, really hot during extended listening (I'm talking hours here).

    The bass is quite solid but not overwhelming (I think the uDac-2 really does help the bass quite a bit over the iMac's on-board sound) and the detail starts to surface with a bit of amplification. The build quality is rock-solid, the only possible weak spot being the thin wire that briefly emerges from the earcup before disappearing into the headband. The cable itself is quite long and very flexible while also feeling sturdy. I also like that the minijack comes with an optional threaded 1/4" adapter, which feels downright bulletproof when screwed on.

    I really do wish my Beyers could have the mind-expanding detail of my SR-225's, but for build quality, isolation and comfort they win on all counts. If you have the budget for a set of $200 closed headphones, I would start with the DT-770's. They're more lively than Senns and quite possibly the most comfortable cans money can buy.

    Thanks for the recommendation on the amps. The Firestones seem like cool little geeky bricks. I like the packaging, although they're more expensive and not pocket-sized like the uDac. I wish that NuForce would hire someone like you to help take the uDac to its full potential. It has the build quality, minimalist good looks and form factor to be an amazing little device, if only they did the necessary research to bring the performance in line with its perceived value. I'd upgrade in a second.

    As it is, I'm debating exchanging it to buy a less sexy, but more refined, alternative. Shame.

  26. Thanks for the Beyer info. There is a pocket Firestone--the Fireye2:


    The closed headphone I was holding out for that's supposedly very comfortable and sounds great is the Fischer Audio FA-003. But their sole North American dealer in Canada is a really small outfit and, AFAIK, has never had them in stock since last fall. So Fischer is apparently either in trouble or they just don't care much about North America.

    So I might give the Beyer's a try for fun. The Denon's sound really good for closed headphones but they're not world's most comfortable for long term wear.

  27. Buy.com has the DT770 Pro-80's for $189 with free shipping right now. Comfort is a big deal to me with headphones, and for that I think the Beyers are unmatched.

    The Fireye2 seems like a solid product, priced equal to the uDac-2HP. It's a shame it's such a dog in the looks department, what with that black plastic volume wheel and weird-shaped enclosure. If only I could shoehorn a Fireye into the uDac2 case, I'd be golden.

  28. Have you spent any time with the HiFiMan EF2A? I'm looking at it on Amazon, and for $169 it's a DAC/Tube amp with both USB inputs (for the DAC) and RCA inputs (for amplifying line-level sources). It only outputs to the headphone jack.

    It isn't portable like the uDac or the little Fireye2, but it looks like a substantial desktop all-in-one rig that's still small enough to lock up in my desk drawer at the end of the day.

  29. I have not had any experience with the HiFiMan tube products. From what I understand they measure poorly because they intentionally distort and alter the sound. Tubes also have other downsides--they run hot, have a limited life, can be microphonic, are fragile, etc. I wouldn't want to be tossing a tube DAC in a drawer every day. And the DAC chip used in the HiFiMan is similar to the one used in the Behringer UCA202. It's not exactly high end.

    If you want to continue this dialog it might be best to use the Contact NwAvGuy link on the right.

  30. What is your opinion about the original Udac? Does it suffer from bad engineering too?

  31. I haven't used the original uDAC but I do know it has even more severe channel balance problems and reviews of it (and the uDac2-hp which uses the same volume control) are generally less favorable.

  32. Thank you m8 for the reply, look forward to more review!

  33. Thank you for publishing this! I was in the market for a uDAC2 and almost pulled the trigger - until I found your blog by accident. Based on my listening station requirements, I went with a Yulong U100 for $225 shipped. It's a well made unit that has got favorable reviews on headfonia and head-fi, and I am pleased with its performance. Keep up the good work!

  34. Thanks for the feedback. I'd hope to test the Yulong U100 someday. I'm writing up my FiiO E7 review now. The E7 is very impressive and a much better option for many applications than the uDAC-2.

  35. Ah, I just wrote a long response that got eaten by the internet... here's a quicker try.

    Essentially, the results with the UCA-202 interest me the most, as I own both the nuForce uDAC-II and the UCA-202 and have compared them extensively.

    If you're implying that the UCA-202 sounds better because of these results, I'd have to disagree quite strongly. It's flat, lifeless, sharp-edged, doesn't image well, and actually hurts to listen to after a short while. Line-Outs, speakers, and headphones alike, I've consistently had this experience.

    The nuForce is quite the opposite. Detailed, crisp, non-fatiguing, extensively realistic, good imaging; I fully believe that it doesn't measure perfectly, but listening experience disagrees that those measurements are as significant to the final result as you seem to suggest.

    Perhaps it's also that I haven't had channel balance or potentiometer issues with mine, overall it's been a good experience.

    I understand the concern for detail, and the scientist in me does appreciate it greatly, but I also have ears and can't ignore them. It suggests to me that there are variables missing that must explain the quality difference better than those you present; either that or issues with the test.

    I know you will simply call me biased, you will say I'm focused on the price difference or something; but I don't think that's the case. You don't need to take selection bias into account when you're differentiating between an apple and an orange; sensory input is quite clear on the reality. If your instruments then suggest that the apple is a citrus, I suggest that perhaps the tests are missing some variables.

    That said, of course unbiased empirical testing is important, and it can only continue to provide better information and performance. Thanks again for your work.

  36. I'm not sure if you read the three listening test articles featuring the uDAC-2 and UCA202? In those tests the UCA202 didn't do as well as its measurements might suggest so you might be at least partly correct. The uDAC-2, however, when driving a pair of IEM headphones was easily the least favorite.

    I've spent a fair amount of time listening to both the UCA202 and uDAC-2 and can safely say any differences are subtle. It's not a case of "apples and oranges" as you suggest. The fact roughly half the participants in the listening test couldn't hear ANY difference backs that up. Perhaps something is wrong with your UCA202 if the differences are really that dramatic--at least via the line outputs? The headphone output on the UCA202, as I've said, has some serious problems.

    The listening tests published here were too informal to yield conclusive results but they should have revealed the sort of huge differences you suggest. The only clear loser was the uDAC-2 driving a particular pair of headphones. I'm planning much better blind listening tests that will be "live" rather than recorded with fewer sources of error and bias.

    I think it's difficult not to be biased when you know what you're listening to. All the hype around the uDAC-2 (from NuForce, in the forums, etc.) tends to bias anyone who buys one into expecting it to sound good--or at least better than a $29 plastic DAC. Sean Olive and many others (see the links in the right hand column of this blog) have proven it's all too easy for such bias to creep into subjective opinions when you know what you're listening to.

    I'm anxious to conduct more research and publish more articles correlating subjective sound quality and measurements. There are still some questions I think deserve better answers.

  37. For those considering the FiiO E7 as an alternative to the uDAC-2, my full review is finally published:

    FiiO E7 DAC & Amp

  38. NwAvGuy, I would like to personally thank you for this amazing article. I don't have any training in your field but even I could follow along with your incredibly detailed breakdown of this product.

  39. I forgot to mention that I like your independent &objective reviews very much... so keep on going :)

  40. I must admit I'm one of those satisfied uDAC 2 owners spreading nice words on the interent (though not head-fi). It makes a very discernible positive difference in my computer-based audio system, and when I went from pretty good speakers (Swan M200s) to better speakers (NHT SuperZero 2.0 with sub) it was even more apparent. I guess it helps that I never put a any volume level higher than about 8 and I don't have anything better than computer sound cards to compare it to. Still, I think it has been worth the price, just based on how much more I've enjoyed my music listening since I bought it. As with anything, there's always better out there.

    I have already thought about eventually upgrading to something more in the $500 range, so I'll have to keep an eye on your site.

  41. joe - don't worry, it's a fine DAC. NwAvGuy is providing an interesting service by measuring it in detail, but if it appeals to your ears and helps you enjoy your music more (as was my experience) then that's great. It's not a bad purchase because someone graphed it, any more than a road is a bad drive once someone maps it. Just enjoy the ride :)

    I too am looking at upgrading at some point, and of course this site will be an excellent resource for half my decision process.

  42. Question: If the headphone output has issues in nuForce and Behringer, but the line out's don't, should one use 3,5mm-2xRCA cable instead and bypass the faulty headphone output? (maybe this was a stupid question... :)

    Thank you a lot NwAvGuy, great site and reviews and much needed new approach into the audiophile world!

  43. RCA line outs won't drive headphones well at all. It's all about impedance. Most line inputs are 10,000 - 47,000 ohms. While headphones are 16 - 600 ohms so they're entirely different. Once I wrap up the O2 Headphone Amp project I'm going to be testing more USB headphone DACs including a Creative and Asus.

  44. Thanks for the answer! Excellent news also to hear about the coming Creative and Asus reviews. I assume they will be X-Fi HD and Xonar Essence One? The latter looks very interesting...

  45. thank you for this. I just got the uDac2 and I'm pissed with the distortion at high frequencies...it's like piercing a needle on my eardrums...i thought i was hearing things until i saw this blog.

    this thing is going back.

  46. I have had experience with the Nuforce Icon HD, HDP, and the uDAC2. All three were returned within a week. There's a lot of snake oil involved with audio and Nuforce seemingly exploits that aspect of its marketing very well. For one, I will never purchase another Nuforce product.

  47. Why were they returned?

    Has anyone done empirical tests on the NuForce Icon HDP? Jan Meyer sells it on his site, and he tends to be very picky and tests everything he makes. I assume he tests other company's products, but don't see any stats.


  48. I've only ever seen a one page summary with a couple graphs per DAC that included the NuForce HDP. The few graphs on that page looked decent enough, but the test conditions were rather unclear. I don't think they were properly measuring the headphone output. That renders the results rather meaningless for those wanting to use it as a headphone DAC.

    NuForce has been caught many times with poorly performing products when others measure them--such as Stereophile did with the $1000 CDP-8. NuForce has also publicly said they basically prefer to design by ear--that was their "excuse" in their letter to Stereophile and to me.

    In my opinion NuForce uses a highly flawed approach in designing all their products. If the HDP is a good product it's probably only because they managed to get lucky.

    Here's a very good example: If you read all the uDAC-2 drama, NuForce claimed they used a volume control with extremely poor 10 dB channel balance error intentionally because they somehow think it sounds better in Subjective Listening.

    They could have used the same Alps RK097 volume control in the very well reviewed high-end Benchmark DAC1. It's only about $1 in the quantities they buy. The Alps part has about 1 dB channel error at the same volume setting their part has 10 dB of error. Yet NuForce claims they selected the horrible part in the uDAC-2 on the basis of their highly flawed listening tests. Really? Can't they hear the extreme channel imbalance? What about all the customers who have complained? Their answer: "We chose it because it sounds better"

    With that approach to product design, I wouldn't trust any of their products. It is my opinion they either don't know what they're doing, or they're cutting lots of corners to maximize their profits and making up excuses when they get caught.

  49. Hi NwAvGuy!
    Based on your two good reviews for Fiio E7 and uDAC-2 on this site and the other

    Could you give me a suggestion for which is the best Portable Amp/DAC should i buy to match with my Sennheiser HD598 for listening music on my laptop and iPod Touch Gen4?

    I'm very confuse about these two options.

    And the other taking into consideration is:
    Fiio E7 Made in China, Is it a cheapest stuff?
    Nuforce uDAC-2 Made in US, Is it perform like its computation?

    Many thanks for your comments in advance.

    P/s: I'll buy the one you mention immediately i read it.

  50. The uDAC-2 is made in Asia not the the USA and, from what I can tell, it's also mostly designed in Asia. The main difference between FiiO and NuForce is NuForce takes a more "high-end" approach, "designs by ear", and charges more for their products. The uDAC-2 is a flawed product. FiiO takes a more practical and cost effective approach.

    The E7 is far better designed than the uDAC-2. Offers many more features for less money. And measures better.

    If you want an amp to use with your iPod Touch the uDAC-2 is useless. It will only work with your laptop. So you want the E7, or if you can wait, the less expensive and likely even better FiiO E10.

  51. I've only come on your testing after buying and returning a uDAC-2. I bought it based on headfi forum raves. I returned it because it was harsh and almost painful to listen to, especially with loudly mastered music (metal, electronica, anything mastered after about 1995 . . .). Now I realize, based on your analysis, that it was probably serious distortion of transients brickwall limited at 0db, which are depressingly common in today's music.

    I am utterly, utterly baffled at why it is so hard to get great sound out of one's computer with less-than-boutique components, and DACs are the biggest mystery. My $20 Sansa Clip and $30 Sony CD/DVD player produce shockingly great sound, but I've thrown too much money at well-regarded DACs and hp amps with scant satisfaction. I have yet to find anything better than my old, dying Chaintech AV-710 sound card, and chafe at having to buy a $200+ DAC to equal that $30 card. But I guess that's where we're at. (Sorry, I'm ranting.)

  52. Anonymous above, you might want to look at the Behringer UCA-202 also reviewed on this site—it seems to have great measurements according to NwAvGuy and others, and operates as a good, baseline, simple and reliable DAC without too many frills for around that $30 price point.

    However I can vouch that once you hit that point where you get a quality DAC instead of the nuForce, you will appreciate it, even though you spent $200 it may be worth it.

  53. Thanks. Yes, I am going to try the UCA-202. It's too cheap not to try. I have an Audinst HUD-MX1 on my home PC that sounds quite good, and was not cheap (ca $180, iirc). But to my ears, the old Wolfson-DAC'd Chaintech card I use at work, through a good-quality CMOY (OPA2134PA), is more detailed and musical, and with a better soundstage. And I would not say the difference is negligible. Unfortunately, it's noise floor is poor, the left channel fades in and out a bit, and it pops and clicks some. I just pretend it's vinyl. . .

    But otherwise I'm resigned to another expensive upgrade, probably an HRT Streamer II. Fingers crossed that it better lives up to the strong reviews.

  54. Or just wait for the desktop version of my O2 amp with the 24/96 USB DAC daughter board (if all goes as planned). It will hopefully outperform anything anywhere near the price. Even the HRT Streamer II is limited to 16/48.

  55. 16/48? They've lied in their specs? Massively disappointing.

    I just ordered the PCB and front panel for the O2 off of DIYaudio's group buys. Though by the time I figure out how to actually build it, I'm sure the desktop version will be out and knocked off on ebay, so I can just buy and use one!

    Never done anything like this before. I guess enthusiast audio turns a lot of people into dyi'ers. I'm ordering my first cmoy kit now. Then maybe I'll try building an RA1 ebay kit before trying the O2. So much to learn. Thanks for both the information and inspiration.

  56. A lot of DACs can do 24/96 via S/PDIF and may even sport 24/192 capable DAC chips. But doing more than 16 bits at 44 or 48 khz via USB isn't trivial--especially for a DIY DAC. There are very few USB chips available to DIYers for high resolution USB and even those are not easy to use.

  57. NwAvGuy, which measurements are likely to have the greatest effect on a device's audible performance? (sorry if this question is somewhat vague)

  58. Hello:
    You stated in your article that the Leckerton Audio UHA-4 has an output impedance of 10 ohms but their site mentions 0.4 ohms.
    Which one is right and which values are ideal for armature IEM's?

  59. @Anon, Leckerton apparently lowered the output impedance of his amps after I published some of my articles pointing out the disadvantages of higher output impedance. For B.A. IEMs you want as low as possible, ideally under 1 ohm but always under 2 ohms.

  60. Hi NwAvGuy.

    Yet another interesting and informative (if slightly worrying) article.

    As both a music lover and someone who also loves engineering, I can see NuForce's angle *to a certain degree*, it should/must ultimately be the sound that counts - but that doesn't excuse what would appear to be fundamentally poor design, particularly the channel balance issue. And let's not forget, NuForce aren't aiming at the budget market. Fiio are significantly cheaper and yet manage to get most of the basics right.

    When you purchase a quality product from a 'serious' manufacturer (i.e. not some random guy on eBay), it should be a given that it should be technically competent in all the ways that really matter for it's particular purpose. If the maker was also managed to find that certain something that also makes it sound stellar, well that's just what separates good from great.

    In the case of a USB headphone Amp/DAC, the two 'must-have' requirements must surely be the ability to handle over-driven/recorded digital sources (i.e. 0db+) gracefully, and to have accurate channel balance across the WHOLE volume range because of the potentially huge variety of headphone sensitivity it may need to deal with.

    Can I just ask which of the more reasonably priced Amp/DACs you have tested would be best suited to low impedance IEMs with balanced armature drivers - around 17ohms? From the what I've seen, most seem to have an output impedance around 10ohms which is too high.

  61. @twelve, I will be testing the FiiO E10 and hopefully publishing the results this Wednesday. I would wait for that review and it may be your best choice for your IEMs if you want a highly portable solution and/or don't want to wait for the ODA/ODAC. Unlike the uDAC-2, both will do 24 bit audio over USB.

  62. "Rich in Bonn" I'm not sure which article your comment about the Tiny DAC and upside down components was intended for but it doesn't seem related to the uDAC-2. I'm really trying to keep the comments to each article on topic and relevant to that article. Please feel free to contact me privately with the link on the right if you like. Thanks.

  63. Man, if only I knew of your website at the time of my purchase. I've been using the uDac-2 for a year now with the HD650, so I found my sweet spot at about 12 o'clock for mainstream stuff. But today, I was feeling in the mood for opera. And with classical, I usually turn it past 12 o'clock, into the danger zone.

    Well, I hadn't really listen to vocal classical for a while, so I popped in Jonas Kaufmann's Verismo CD, and noticed his voice was getting quite ugly in the louder passages. How do you mess up classical music?! Pissed me off enough to find your website. I turned down the volume back to the sweet spot, and lo and behold, clipping gone. Shoot, I can understand Lady Gaga clipping but opera?

    I'll be retiring the uDac-2 soon enough. I've purchased a Schiit Lyr since I've read it pairs with and powers nicely the HD650s (well depending on the tubes you play with of course) but I'll have to use the uDac-2 as... well, a DAC, keeping the pot at about 11 or 12 indefinitely. I'll probably update my DAC in April after paying off other obligations, but will also be doing extensive research for one that doesn't perform abysmally as the uDac-2. I'll be looking at your website in the interim for that DAC.

    Thanks for your awesome work, NwAvGuy.

  64. Hey NwAvGuy. First of all thank you for this and your many other extensive reviews (I've read through just about all of them in the last day)!

    As one of my local stores has a sale on the NuForce Icon-2 (to ~$200) I was hoping to purchase it as a desktop USB DAC for my laptop which doesn't seem to do all too well on audio (especially the lower volume portions apparent in classical music). However after reading this review I'm no longer so sure. I imagine that most NuForce DACs would suffer from the same issues due to their "Design By Ear Policy"? Have you had a chance to listen to the NuForce Icon-2 per chance?

    Thus I am looking at alternatives in the same price range (~$250) and the only other option I can easily get my hands on is the Arcam rPac (seems to get excellent reviews), Audioengine D1 or the FiiO. However, I would rather go for something that can drive a wider range of higher impedance headphones (than my current HD595s) than the FiiO E10. Do you have any experience with the Arcam rPac per chance? I like local built :p . Or any other suggestions?

    Lastly, it always annoys me that companies that claim to produce quality and (mid) high-end products like NuForce can afford be produce something 'flawed' or seemingly without proper testing as you have shown and just deflect any criticism. And as much as I can understand that in the end what matters to most is that it 'sounds good', the numbers should (and would) reflect that...

    Thumbs up again for the great blog!

  65. Hello NwAvGuy!

    Several times you have mentioned the EMU (E-Mu)0202 .
    It would be great to see you measure it to Kingdom Come
    because NEVER have I been so disappointed with the actual performance,
    relative to the claimed specs, for a device .
    (Regarding the 'Class A' headphone amp my expectation-bias was already on 'Low' because there's a limit to how much you can expect from 5V, 250mAmp USB power-supply .)
    However, the thing SOUNDS horrible when used for play-back, despite the very decent specifications stated !

    One thing I have noticed :
    ProcessExplorer from windows sys-internals reveals periodic 50-60% CPU-usage on DPC's (Deferred Procedure Calls). On my system this happens when the device is set as default sound-device and there is sound playing OR if another sound-device is set as primary AND the 0202 is selected as audio-device in fex foobar and playing sound.

    This unit has sold relatively well to home-musicians, the stated specs suggest it should be 'transparent', yet it SOUNDS like c¤#% !! and everywhere you look on the internets, people keep talking about how horrible Creative/EMU drivers really are!

    Now, you have the hardware and the knowledge to use it properly :
    What IS wrong with that thing ??
    I suspect it's worse than a buggy driver, ie buggy firmware !

    1. I'm really curious to hear this as well, because my experience exactly mirrors yours: the UCA-202 sounds absolutely horrible!

      I think absolute measurements will break down here. Thr nuForce is by no means ideal, but there's a missing puzzle piece. The UCA202 is not a high quality device.

    2. If you're listening to the headphone output of the 0202 that's likely the problem. It has a horribly high output impedance. If you think the line outputs sound bad, I would have to do more research. But, my first answer, is it's probably sighted listening bias (i.e. what you're hearing would dissappear if you were listening blind). It's also possible the driver is mucking things up somehow.

    3. Hello NwAvGuy,

      I am also an engineer and I do respect the way you process your tests ( including the blind ones ) and I was looking forward to hearing this UCA202 DAC ( to listen to music from my PC to the audio amplifier ).
      I wished to buy a more expensive DAC but I bought this one after I read your excellent technical review and I didn't care about the headphone issue. But, on my audio system it is disappointing. This afternoon,I did a lot of tests trying to find out why it sounded bad. The sound was like Tristan described formerly. Maybe, I got a defective one.
      My pretty old audio system is composed of : galion Cabacce speakers, Nakamichi amplifier, Marantz CD6000 and Seinheiser HD650.
      Hopefully, you'll get what I wrote. I am not fluent in english.

      Best regards


  66. I've read your article with much joy a while ago and just now decided to take a look at some of the feedback on amazon. What's interesting is how quickly nuforce leaves a response to everyone giving their product a low score. If you leave a bad review, first thing NuForce tells you is how great their product actually is and that you can see this by looking at the dozens of positive reviews. We all know how informative subjective reviews are, and besides that, i don't want to know how many reviewers are affiliated with or sponsored by nuforce...

    My favorite quotes: "I think the overwhelming number of positive reviews speak for the performance and quality of uDAC-2."

    .- Customer service: -.
    I actually liked the comment where nuforce bluffed out of a situation where their customer service didn't respond to a customer who had a defective unit. The reviewer's unit failed and he contacted nuforce. Accordign to him they never responded to phone calls and it took them two to three days to answer to a email. It took him 30 days to get his refund. To quote the reviewer: "When the unit worked it sounded okay, not great. But if the unit fails, and it probably will, good luck trying to get support for this poorly made product."
    NuForce responded that their senior support staff was seriously ill for three weeks and the senior engineer on family vacation. Okay that can happen, but if you know that staff members are ill and on vacation, wouldn't it be a good idea to look for a substitute? And this is especially flimsy when another person joins the comments claiming that he received the exact same excuse just months ago...

    Another reviewer received a unit that had some sort of "crackly, noisy sound quality". He contacted NF and they send a replacement unit that dies shorty after. Then a third unit that died. Then he received an answer from them that his "uDac-2 (is) out of warranty".

    .- udac not suited for headphones? noisy usb dac's? -.

    Quoting another reviewer: "I really wanted to like the udac but the sound coming from the udac into my Audio Technica ATH-AD700 headphones was just ever so slightly WORSE than the onboard sound on my desktop. It slightly muffled the and blended the low end together and cut out some detail from the high end. I performed several A/B comparisons of the udac output vs the headphone port on my desktop and some songs experienced the slight loss of detail described above and there was no discernible difference for the rest. "
    "There are two main factors that affected your experience with uDAC-2.
    1) uDAC-2 is primarily designed for in-ear earphones and most easier to drive headphones. Audio Technica headphones typically draw a lot of current, so you get everything blend when uDAC-2 can not drive it. Our Icon HDP is suitable for headphones.
    2) Another possibility is that your laptop USB hub is noisy and underpowered."

    Great, if your product is faulty, tell your customer that his usb hub could couse this.

    And if you're still not conviced that the product you have bought is actually good, they will constantly hint you towards a couple of demo tracks on their website that will fully convince you once you listened to them. I wonder what brainwashing messages they recorded, but according to them, these four songs convinced one of the negative reviewers to rate the product from 1 to 5 stars. I'm sure the guy received more than the four songs from nuforce to be convinced enough for a 5-star rating.
    You should also burn-in the product for at least 20hours. Like that would fix the high impedance issue, channel imbalance and so on, right? :)

    "Many customers are extremely happy with our service and posted 5 stars feedback. If our product is inferior, how can so many customers be wrong?"

    Thanks nwavguy for playing G.I. Joe against the Cobra regime!

  67. For what it's worth it seems NuForce is now actually measuring the things they sell, if the page for their DAC-100 whatever is anything to go on based on it being plastered with graphs now.


    Oh my, it appears they've been measureing a lot of other people's DACs as well:


    Haha, I think in that PDF I just found a great example of the high end audio product, the sort of example that you might use in a Plato's Cave analogy. That "David Weiner" DAC doesn't seem to really do anything right and based on their company's apparent desire to make giant speakers with fake NACA ducts machined into them that also seem to serve double duty as crushing hazard if one fell over (Their enclosure seems to be machined aluminum) gives me the impression that this DAC costs somewhere north of $1,000. Their site talks a lot about inspiration from Ferrari for some reason, take a look:


    This is like the mini dead sea scroll of the audio world.

    1. First of all, I'd like to think I deserve some of the credit for NuForce publishing better measurements. They made several changes downgrading the specs for the uDAC-2 after this article was published. And I've helped create customer expectations for published measurements.

      There are many important measurements missing from the PDF you linked. So it's only a partial picture of the total performance and not enough to determine if the DACs would be audibly transparent. Further the test conditions (levels, etc.) vary between products and some important conditions are not specified at all.

      Without specifying more test data, a manufacturer could for example be comparing their DAC running in 24 bit mode with a -1 dBFS input to Brand X running in 16 bit mode at -10 dBFS. Such a comparison would heavily favor their product.

  68. Thanks for doing all of this analysis. I feel like there's a lot of snake oil in audio, but don't know enough to point it out. This helps out us newcomers, who might otherwise fall for the tricks (esp. w/ headphone cables)


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