[nwavguy]

Hopefully others agree this belongs in its own thread and not lost among the 50+ pages of the other uDAC-2 thread. That thread is mostly about subjective issues, while my blog review is more about some very questionable objective measurements and the response I received from NuForce. They asked me to include their final comments in my review and I have done so.
 
I highly recommend anyone considering a NuForce product--especially the uDAC-2 (or uDAC2-hp) at least have a look. I put a lot of my personal time into the measurements, communications with NuForce, and the final article on my blog.
 
It also seems NuForce may be a sponsor here. If so, I would hope the moderators and administrators take this for what it is--objective information for those interested. I have no connection with any DAC manufacture of any sort and it's only a personal blog.
 

 

[attenuated 3db]

Wow! I read your entire blog post on your measurements of the uDAC-2 (which I own the $99 headphone-output only) model of, and it was a real eye-opener. Not sure my ears can appreciate all of your incredibly detailed data, plus the extraordinary exchange of information with Nuforce regarding it. Here is a post I made recently to another uDAC-2 Head-Fi-er:

http://www.head-fi.org/forum/thread/197776/sennheiser-hd650-appreciation-thread/2595#post_7304127

"jasonl" is the Head-Fi-er who has always (to my mind) represented Nuforce products in candor and detail with the rest of the community, and clearly has the "MOT" ("member of trade") designation to show that he has a personal interest in the commercial success of his employer's products. I am sure he will see this thread, and have some sort of public response.

And I appreciate what you say about sponsor-supported publications and websites versus something totally non-commercial like your personal blog research. It is one of my few gripes about Head-Fi.org. I use two ad-blockers extensions with my Google Chrome web browser, and when I am at the public library and stuck with Microsoft IE and don't have the benefit of my own home computer set-up, I see all of the colorful ads I otherwise never see.

I am convinced it is the main reason that "boutique" headphone cables get so much attention on Head-Fi. Their makers are major advertisers, and I am of the firm belief that cable fabricators have relatively high profits margins on their products given their "parts" costs, so they can afford to sink more into advertising, to counter the efforts of those of us who would prefer to spend more time "debunking" uber-expensive cables than saying how they cure all sorts of audio ills that an LCR filter circuit (which is the only role a cable plays in an active component chain) couldn't possibly cure, and certainly not at the astronomical asking prices for some of them.

 

[spc100]

Thanks for the info and taking the time to do this. I really appreciate it. I think I am back to behringer or emu for my (future purchase) low cost USB DAC for headphone usage!

 

[nwavguy]

You're both welcome. I'm glad you liked my uDAC-2 review.
 
@attenuated 3db, I've had contact with Jason from NuForce already (assuming it's the same Jason). He seems friendly enough and I was impressed with NuForce's responsiveness. But, unfortunately, I'm not nearly as impressed with their product or explanation why it is the way it is. But hey, if NuForce introduces a uDAC-3 and it's better than the competition, I'll be the first to recommend it on my blog and in the forums. I have my issues with Apple too but I readily admit my iPod has some impressively great audio measurements. It easily beats the uDAC-2 by a wide margin in all but output power and having similar output impedance.
 
Don't even get me started on cables. That's one thing Audio DIffMaker does really well. It compare cables under real world conditions and determines if there are *any* differences at audible frequencies--even really tiny ones. The "LCR" filter circuit you mention only matters if it has any significant effect at audible frequencies. And it rarely does (although some intentionally alter the sound). These days we have cheap cables that can accurately transfer signals in Gigahertz territory (USB 3.0, HDMI, SATA, etc.). Audio frequencies, by comparison, are child's play.
 
And I've been to the wholesale trade shows with booth after booth of Chinese cable vendors looking for companies to retail their products. It's kind of fun. They often have samples of 50+ different kinds of exotic looking bulk cable, and 50+ different fancy metal connectors, and you just have to say I want that cable, with these connectors, printed with my Uber Tweak Cables logo every 6 inches and they'll make you thousands of them. No R&D into crystal-aligned moon-phased oxygen free unobtanium required! As you suspect, the profit margins are obscene. And I won't even mention the company name on show badges doing a deal in such a booth.
 
@spc100 As for low cost USB DACs I hope to try and test a few more options. It's hard to understand why, but some products get a huge following in forums like this one, and sometimes even better products get largely ignored. I hope to uncover some of the "even better ones" in apples-to-apples objective comparisons. Based on measurements I've already made, the E-mu 0202 will outperform the Behringer UCA202 as headphone amp, but E-mu's drivers are a bit of a mess while the UCA202 doesn't need any.
 
I plan to do a more detailed article on the E-mu 0202, 0404, and M-Audio Transit. But they all require special drivers optimized for low record/play latency which musicians want for live recording. Unfortunately such drivers have to get their "hooks" deep into the operating system, and use small buffers, to improve the latency and that often causes other problems. For simple playback of audio (no live recording) latency is not an issue and the built-in Windows drivers are usually much better. So from that aspect the Behringer has a big advantage over the E-mu.
 

 

[nick_charles]

Quote:

 
It also seems NuForce may be a sponsor here. If so, I would hope the moderators and administrators take this for what it is--objective information for those interested. I have no connection with any DAC manufacture of any sort and it's only a personal blog.
 
 

Very interesting !  - could those of us in the back of the bus persuade you to bring your test kit and methodical approach over to the Science forum from time to time. You would be a very valuable contributor to us "pseudoscience" types.  I am also amused to see how well (relatively) the  $29 Behringer holds up, I have one of those little doodads.
 
 

 

[allyl]

The time and effort you put into this review is much appreciated!
 
Now I feel far better about returning mine to buy a NFB-12

 

[nick_charles]

That is my territory, this is mostly about (Group) Psychology and Psychophysics. Many audiophiles do not listen solely with ears and brain but also with eyes and wallets and under peer influence. This allows all sorts of cognitive biases to come into play, expectancy, recency, primacy and so on, also the more often a myth is repeated the more likely it will become accepted as fact. Then there is the whole issue of what level of difference is audible anyway - compared to your measuring rig humans have pretty poor powers of discrimination such that a nosie level of -100db and one of - 106db will be indistinguishable...at normal levels anyway.
 
Quote:

 
@spc100 As for low cost USB DACs I hope to try and test a few more options. It's hard to understand why, but some products get a huge following in forums like this one, and sometimes even better products get largely ignored. I

 

[129207]

Thanks for your awesome contribution to this community! You're doing valuable work (and I'm sorry you're not making any money out of it). All you need is someone to rewrite your musings and findings into a catchy and reader-friendly whole and you've got yourself a mighty blog!  

 

[attenuated 3db]

You're both welcome. I'm glad you liked my uDAC-2 review.
 
@attenuated 3db, I've had contact with Jason from NuForce already (assuming it's the same Jason). He seems friendly enough and I was impressed with NuForce's responsiveness. But, unfortunately, I'm not nearly as impressed with their product or explanation why it is the way it is. But hey, if NuForce introduces a uDAC-3 and it's better than the competition, I'll be the first to recommend it on my blog and in the forums. I have my issues with Apple too but I readily admit my iPod has some impressively great audio measurements. It easily beats the uDAC-2 by a wide margin in all but output power and having similar output impedance.

Well, I like to give people (and small companies) the benefit of the doubt. Nuforce had a very inexpensive DIY upgrade to make a uDAC into a uDAC-2 with a simple board swap anybody could perform, giving it instant 24/96 file support from the previous 16/48. And as someone pointed out, you could actually keep your old uDAC board and mount it in the ubiquitous CMOY Altoids mint alumnum can, and have a second, back-up USB DAC. So perhaps Nuforce just didn't know their own product as thoroughly as your tests measured it. Happens all the time at the U.S. Food and Drug Administation, U.S. Department of Agriculture, National Transportaion Safety Board and Federal Trade Commission when product recalls have to be issued for hidden product flaws that are genuinely dangerous. Don't think anyone will be injured by their uDAC-2; mine has yet to bite me, and I'm listening to it as I type this post. It's a great mobile soundcard for any laptop or netbook due to its small form factor, and even if the current circuit may have flaws, I like the ruggedness of the case for easy throwing into a netbook bag without fear of breakage.

 
Don't even get me started on cables. That's one thing Audio DIffMaker does really well. It compare cables under real world conditions and determines if there are *any* differences at audible frequencies--even really tiny ones. The "LCR" filter circuit you mention only matters if it has any significant effect at audible frequencies. And it rarely does (although some intentionally alter the sound). These days we have cheap cables that can accurately transfer signals in Gigahertz territory (USB 3.0, HDMI, SATA, etc.). Audio frequencies, by comparison, are child's play.
 
And I've been to the wholesale trade shows with booth after booth of Chinese cable vendors looking for companies to retail their products. It's kind of fun. They often have samples of 50+ different kinds of exotic looking bulk cable, and 50+ different fancy metal connectors, and you just have to say I want that cable, with these connectors, printed with my Uber Tweak Cables logo every 6 inches and they'll make you thousands of them. No R&D into crystal-aligned moon-phased oxygen free unobtanium required! As you suspect, the profit margins are obscene. And I won't even mention the company name on show badges doing a deal in such a booth.

Yeah. Please post more on this in the Sound Science forum. Measure some popular Sennhesier 600/650 cables and show the "return on investment" their potential purchasers can actually expect. Because Sennheiser used the detachable connectors that George Cardas copied, they opened the flood gates to easy-to-replace aftermarket cables that cost as much or more than the HD650s themselves. Please post more on this, like you did with your uDAC-2 "expose."

 
@spc100 As for low cost USB DACs I hope to try and test a few more options. It's hard to understand why, but some products get a huge following in forums like this one, and sometimes even better products get largely ignored. I hope to uncover some of the "even better ones" in apples-to-apples objective comparisons. Based on measurements I've already made, the E-mu 0202 will outperform the Behringer UCA202 as headphone amp, but E-mu's drivers are a bit of a mess while the UCA202 doesn't need any.
 
I plan to do a more detailed article on the E-mu 0202, 0404, and M-Audio Transit. But they all require special drivers optimized for low record/play latency which musicians want for live recording. Unfortunately such drivers have to get their "hooks" deep into the operating system, and use small buffers, to improve the latency and that often causes other problems. For simple playback of audio (no live recording) latency is not an issue and the built-in Windows drivers are usually much better. So from that aspect the Behringer has a big advantage over the E-mu.
 

Other than my uDAC-2 "HP" (with the potentiometer from the older uDAC, which Nuforce admitted had a channel imbalance problem although they avered it to be slight, and my hearing is not keen enough to detect it with casual listening), I have a Maverick Audio "Tube Magic" D1 DAC/preamp (Cirrus Logic chipset) and will be selling it as soon as my Audio-gd NFB-3 arrives next week. At $200 and $300, respectively, they are not budget, but upstart Maverick and long-time Head-Fi favorite Audio-gd have huge followings on this website, and I would like to know how the products measure. There was a dust-up a few weeks back in the Audio-gd NFB-12 thread (at $200 a budget DAC/head-amp) about digital filter implementation with a dual Wolfson 8741 D/A converter chip design.

Ok, if I type any more, a Head-Fi moderator is going to tell me to "get back on topic" even though its a brand new thread., or move it to the "Sound Science" forum. So I will stop for now.

But thank you for your "investigative audiophile journalism," even if you had to "self-publish" it.

 

[nwavguy]

 
Quote:

Other than my uDAC-2 "HP" (with the potentiometer from the older uDAC, which Nuforce admitted had a channel imbalance problem although they avered it to be slight, and my hearing is not keen enough to detect it with casual listening) ...

But thank you for your "investigative audiophile journalism," even if you had to "self-publish" it.

You're welcome. And the thing about cheap potentiometers (aka "pots") and channel balance is you may well get lucky and get a good one. Not to geek out too much here, but the way they're made it's essentially a random pairing of two different single pots into a stereo pair. And, if they're not individually tested and sorted for their tracking ability, what you end up with will be very random. Some people might draw two aces in a row from the deck of cards. Others might get a 9 and a 2. So it's entirely possible you have one of the better ones if you're not hearing audible tracking problems.
 
And it also matters a lot how efficient your headphones are and if you listen with everything set to max volume on the PC side for a bit accurate stream to the DAC. With low sensitivity headphones, or if you turn down the volume in the software player or PC's mixer, you'll likely not run into the lowest part of the control's range where the balance error can get really bad. But, trust me, even the 8.8 dB that NuForce measured on their sample is VERY audible. Some players and applications let you set volume and/or channel balance in dB. So it's easy enough to hear what 9 or 10 dB of balance error actually sounds like. Your Grandmother could probably hear it.
 

 

[bcwang]

I agree the design decisions you've uncovered don't make sense to me either.  The volume tracking issue is also definitely a big problem especially at the lower settings with sensitive headphones.  It really surprised me that you found out they could have lowered the gain in such a way to mitigate this issue and prevent the distortion at full scale output but chose the opposite path.  I think if they did that I'd have found the uDac2 more usable than I currently do.    I also never used the uDac2 as a line level DAC where I'd instinctively turn it to max volume, but it sounds like it would sound bad as well used that way. 
 
Welcome to head-fi and I hope to see more on your interesting blog.

 

[nwavguy]

@bcwang The best solution to the gain problem is 2 gain modes like the Leckerton UHA-4 has. Firestone also has it on their better DACs.That way if you have high efficiency headphones you can run the DAC in "low gain" mode and it will be much quieter, the volume much less "touchy" and you can use far more of the volume control's range. And those with power hungry cans can run it in "high gain" mode to get enough output voltage for their headphones. It's the best of both worlds and doesn't cost much to add to the design.
 
The Leckerton is only $40 more than the uDAC-2 and, in addition to 2 gain modes, you get an internal Li-Ion battery for portable use, Linkwitz headphone crossfeed, made in the USA quality, a 2 year warranty, and a really high-end Analog Devices headphone amp running from split +/- 5 volt rails (which give it double the voltage capability, eliminates the need for output and coupling capacitors, and generally enables much lower distortion and better performance). I regret not buying it instead. There's a Head-Fi review on the UHA-4 here:
 
http://www.head-fi.org/forum/thread/536982/leckerton-audio-slimline-uha-4#post_7240176
 
And a well done set of measurements posted on the Leckerton UHA-6 that implies Leckerton as a company really knows what they're doing here:
 
http://www.leckertonaudio.com/2011/01/uha-6s-harmonic-distortion/
 
And you don't want to just turn the volume to max with the uDAC-2 when using the line outs. Even the line outputs can go into hard clipping with the volume all the way up at. I think around 1 oO'Clock on the uDAC-2 volume control is the most you can use if with the PC volume at max.
 
And, just to be clear, the uDAC-2 suffers from two very different kinds of clipping (I might need to make this more clear in my blog review):
 
The first kind is more the normal kind. At some point the headphone (or line) output clips if the output too high. A lot of headphone amps and DACs clip before full volume. So this part isn't that unusual but it would be nice if it happened at a higher volume setting than 1 O'Clock. That's one reason I suggested less overall gain.
 
The second kind of clipping is unique (as far as I know) to the uDAC-2 (and perhaps other NuForce products?). It's essentially "internal" clipping of the DAC circuit itself due to the input signal (via USB) being too high for it. It has nothing to do with the position of the uDAC-2's volume control. Even with it turned almost all the way down so you can barely hear the music, the uDAC-2 will still clip and distort any peaks that get close to a digital input level of 0 dBFS from the PC.
 
If you have your PC volume at full to avoid loss of resolution, and play typical pop music, the peaks may frequently get close to 0 dBFS because pop music is usually mastered that way by design. If you do a straight rip (without volume leveling) from a typical pop CD these peak levels are transferred to the MP3, AAC, FLAC file, or whatever, and the uDAC-2 will clip on them. And some music software has a normalization feature that automatically adjusst the track so the loudest peaks hit 0 dBFS regardless of how the CD was mastered. And, in either case, the uDAC-2 doesn't like those peaks unless you turn down the volume on the PC side which causes the stream to the DAC to no longer be bit accurate and less than full 16 bit resolution.
 
I hope that helps.
 

 

[jasonl]

This will be our only response to the uDAC-2 measurement. We received the email about your measurement on Friday afternoon. And our measurement lab is in Taiwan, close to our contract manufacturer.  That's why we have to travel to another company's lab to take measurement, in order to check out your claim. We have design staff in US and Taiwan and the engineer who is responsible for uDAC-2 works in Taiwan, which is already Saturday. 
After all the drama as you called it, we reached the following conclusion. And I am copying it directly from our email without any change.
Again, this is the way we have decided to design uDAC-2 and overwhelming majority of customers love and rave about the sound quality. If someone choose to listen with their measurement equipment, there is nothing we can do.  I will conclude with another example such as our OPPO BDP-93 Nuforce Edition. We designed it so that it sounded like solid state triode, with a FR curve that looks WORST than the original BDP-93 and some people were also complaining about it. Our BDP-93NE has other measurements that are much better and I won't go into it here. My point is that we can not simply rely on measurement to make decision for good sounding audio products.
uDAC-2 volume imbalance at low level is a big issue for a few people and they complained loudly to us. A digital volume control would fix this problem. But we insist on using this rather expensive volume pot imported from Japan because IT SOUNDED GOOD!  Believe me, we have tried to switch volume pot, but to us, better sounding product still win hands down over better measured product.
 
------------------------------------------------------------ from email exchange ------------------------------------
 
Your uDAC-2 is within spec, and both of our measurements are correct, just that we are looking at different part of the plot. Please read the response below (there are many questions so if we missed anything, please let us know). 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.

> Thanks for the response and running some tests. A PC should not clip a 0 dBFS signal. I think the uDAC-2 is the problem. Here is why:
>
> I can play a 0 dBFS signal on the PC in Foobar 2000, Windows Media Player, or let the dScope generate a "soundcard signal" where the uDac-2 is the "soundcard". Any of these 3 methods gives much higher distortion at 0 dBFS than at -1 dBFS.
>
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. We are not being arrogant and disrespectful to your approach with your measurement, uDAC-2 is a product designed for general consumer use, so it has to work well for their most common use cases (there are more such cases below).


> I can play the exact same 0 dBFS test file as above with my Benchmark DAC1 Pre connected via USB and it is OK with very low distortion.
> I can play the exact same 0 dBFS test file as above even with my PC's internal sound chip and even it has lower distortion than the uDAC-2.
> So I believe the uDAC2 is doing something wrong with 0 dBFS signals. I also disagree that "nobody listens at 0 dBFS". When you turn down the volume on the PC with the Windows mixer the bitstream to the DAC is no longer bit accurate. You lose bit resolution (< 16 bits) as Windows is reducing the level in the digital domain. So many people DO listen with the mixer set to maximum. In fact, many DAC manufactures suggest you listen that way (including Benchmark) to avoid losing resolution and get the full 16 bit stream to the DAC.
>
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 many pop recordings are now heavily compressed and the signal often hits 0 dBFS in regular music. And many people normalize their music to 0 dBFS when they rip CDs. So peaks of 0 dBFS are very common. And the uDAC-2 is going to perform poorly on those peaks.
>
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 uDAC-2 also clips at about 1 O'Clock and 0.9 volts (with 0 dBFS input) so at least we agree on that. That is OK.
> As for soundcards and RMAA those measurements usually cannot be trusted. Many things go wrong with RMAA and most people do not know how to properly test a USB DAC. Very few have any way to measure or set the levels, proper loads, etc.
> The channel balance is very bad on my sample. At some settings the error is more than 10 dB! Please see the attached screen shots of measurements showing different volume settings from 9 O'Clock to 12 O'Clock.
 
At 9 o'clock, there is hardly any signal, and analog pots do not behave well.
At 11 o'clock, your uDAC-2 slightly worse than our target, but 1dB is not unreasonable.
I will show you that a sample I had practically perfect L/R tracking (see attached file).
9 o'clock is off position.
11 o'clock is 1dB

Volume at 9 o'clock (-41.6 db below reference): Balance Error: 8.8 dB
Volume at 10 o'clock (10 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.


> You can't tell if it is new or old from the serial number? It's from Crutchfield. They are very good with returns so I know they will take it back when I am done testing it.
> The problem is not noise, I think the distortion is a design problem. And the channel balance is a very cheap volume pot with poor quality control.
> Here are 3 more screen shots this time with Line Out:
> 1 - uDAC-2 playing 0 dBFS 1 Khz at 1 volt into 100K Line Out 0.17% THD
 
I confirmed that the ESS DAC clips at 0dB digital signal.  If we do not do that, then at typical music, the output could be very low.  We learn this the hardway with Icon Mobile and Icon-1, where many people said the USB music lacked volume and dynamic.  So we have to dial up the mid-level signal and let the extreme level clips.  THD drops as long as the digital input is kept below -1.3dB.
Like I stated above, we tuned it for most common use cases as we learned from past experience with Icon Mobile and Icon1.


> 2 - Benchmark DAC1 Pre playing same file, same PC, same dScope settings, 0 dBFS 1 Khz 1 volt 100K 0.0007% THD
> 3 - uDAC-2 -115 dBFS (ref 1 volt) 1 Khz to show noise floor - noise is OK (< -120 dB)
> 4 - uDAC-2 Spectrum from 40 Khz to 50 Khz. Note the 48 Khz signal but I'm using 44.1 Khz input.
> Picture #1 shows high distortion even with Line Out at 100K. #2 shows it is not my PC or the USB connection--the Benchmark plays the same file OK. Picture #3 shows this problem is not noise. And #4 shows the uDAC-2 seems to be resampling 44.1 Khz to 48 Khz? You can also see a 48 Khz signal in #3. This is not good when most listen at 44.1 Khz.
 
The uDAC2 has no re-sampling capability.   It throws out whatever is fed.  If the Windows re-samples, it could be reflected.  A lot of issues and difficulties because there is too many s/w possibilities.

Best regards,
Jason Lim
CEO, Nuforce

 

[bcwang]

 
Quote:

And, just to be clear, the uDAC-2 suffers from two very different kinds of clipping (I might need to make this more clear in my blog review):
 
The first kind is more the normal kind. At some point the headphone (or line) output clips if the output too high. A lot of headphone amps and DACs clip before full volume. So this part isn't that unusual but it would be nice if it happened at a higher volume setting than 1 O'Clock. That's one reason I suggested less overall gain.
 
The second kind of clipping is unique (as far as I know) to the uDAC-2 (and perhaps other NuForce products?). It's essentially "internal" clipping of the DAC circuit itself due to the input signal (via USB) being too high for it. It has nothing to do with the position of the uDAC-2's volume control. Even with it turned almost all the way down so you can barely hear the music, the uDAC-2 will still clip and distort any peaks that get close to a digital input level of 0 dBFS from the PC.
 
If you have your PC volume at full to avoid loss of resolution, and play typical pop music, the peaks may frequently get close to 0 dBFS because pop music is usually mastered that way by design. If you do a straight rip (without volume leveling) from a typical pop CD these peak levels are transferred to the MP3, AAC, FLAC file, or whatever, and the uDAC-2 will clip on them. And some music software has a normalization feature that automatically adjusst the track so the loudest peaks hit 0 dBFS regardless of how the CD was mastered. And, in either case, the uDAC-2 doesn't like those peaks unless you turn down the volume on the PC side which causes the stream to the DAC to no longer be bit accurate and less than full 16 bit resolution.
 
I hope that helps.
 

The two types of clipping was pretty clear in your article.  The first kind I can understand when the headphones are driven to a high level and the amp runs out of steam.  Fortunately this never occurs for me since I listen at apparently so low a level I am always on the threshold when both sides equalize in volume.  But when in line-out mode I can't really say it is justified to have clipping at any point.  In fact I'd expect to get the best SNR ratio and dynamic range at full volume where as much of the volume pot is out of the way of the signal as possible.  This is exactly the reason why I don't like variable line-outs and prefer fixed outputting at the right line level.
 
As for the second type of clipping, I agree that it's not what I'd want either.  I'm very sensitive to clipping distortion and it bothers me when music clips.  When I tested the uDac2, I used audiophile music which is generally recorded quite below clipping level and is probably why I didn't notice the unit causing self induced clipping.  If I had used pop music I might have attributed the clipping to the music unless I was familiar with it, maybe this is the reason it isn't noticed by many users.  But for a purist it does bother me as well to know about this problem.  I guess it's true that knowing too much about how a device measures can drive you nuts. 
 
I wish I had an audio analyzer myself...or maybe it's better that I don't ever have access to one or else....
 
 
 

 

[busyx2]

According to Stereophile, definition of clipping is '1% THD+N'.