MUSINGS: Evidence of digital player jitter with asynchronous USB DACs? Melco N1ZS20/2 review in HFN&RR...

The UK magazine Hi-Fi News & Record Review is interesting. Like Stereophile here in N. America, it includes objective measurements. Over the years, I've seen times when they have criticized questionable "hi-res" downloads showing nothing more than upsampled music. But they also seem to like "showing" rather meaningless measurements such as a few years ago with their USB cable roundup.

Recently, I believe in the May 2017 issue, they reviewed the very expensive "cost-no-object" digital server - the Melco N1ZS20/2. This device is the "mk2" of their top-of-the-line music server/player with the capability for data output through ethernet or USB connection to one's DAC.

Let's get the "elephant in the room" out of the way - yes, it costs... a lot. We're looking at a device that's listed as starting at £2099 and goes up to the £7700 top end which is what was reviewed and measured. That top end machine is about US$10,000. That's 5-figures for a low-power computer server (they don't say what CPU but I presume a fanless ARM, nor mention what amount of RAM is inside; BTW you can see the "stripdown" of their lower end first generation N1A here). For the price, there's no built-in DAC, with 2 x 1TB SSD drives.

As I have expressed in the past, non-utilitarian functions cost money. I'm totally OK with any company asking an arm and a leg for a product - fancy cars, nice handbags, beautiful clothes, jewelry, watches... A $10K low-power computer server - why not!? After all, it's got "heavy aluminium extrusions, bead blasted to a beautiful anodised finish", weighs 19 lbs, has "a single press power button", "comfortable front panel buttons with positive click for easy operation", "OLED display to reduce internal noise", "TAOC vibration isolating feet", among other "interesting" features and "desirable" talking points. Also, 1TB SSDs are still pretty expensive although one should be able to get a couple of Samsung 850 EVO 1TB drives for around US$650 these days. Let's just say I've got some doubts about firmware hacks to make SSDs "Audio Grade" - LOL! :-)**

However, what I think bothers many reasonable audiophiles are claims about the utilitarian improvements offered by these kinds of devices - the ability for actual improvement in hi-fi sound quality. There's a desired impression that the cost can be justified by "better" sound, presumably a significant and noticeable difference.

As I mentioned above, HFN&RR is an interesting publication that posts objective results. Have a look at this review of the Melco; freely accessible from the Melco website by PDF. In it, there are claims being made which really deserves some exploration and thought.

First, feel free to explore the subjective review of course... It's the usual golden-eared commentary about how this is the very best. Sure. More "clarity and focus", "greatly improved", "better slam and drive" to the bass frequencies, "drive and pace of the music is enhanced"... OK, so the reviewer thinks it sounds better than his "£200 secondhand Mac mini".

What is much more interesting are the objective results, supposedly proving change in jitter performance and noise level with some DACs compared to a "standard PC" via USB. They show some numbers in the "Lab Report" section, but much more visually interesting are the graphs. For reader convenience and since the PDF is freely downloadable, why don't I reproduce the graphs in the article here for the purpose of criticism and discussion?

This first graph is of the Melco connected to the iFi iDSD BL; a ~US$450-550 DAC that's really meant for desktop headphone listening and RCA outputs only. As labeled, in red is the DAC connected to a "standard PC", and in black the Melco. It shows that there's more noise in the background and noise spikes with the "standard PC" connection and more "skirting" of the base of the J-Test peak at the primary frequency to indicate more low-frequency phase noise/jitter. They claim that the jitter difference showed a "marginal improvement" from 105ps to 140ps in the summary table. Notice that there are some symmetrical, probably jitter-induced sidebands that actually look to be of similar amount between the "standard PC" and Melco. Other than that single red noise peak in the "standard PC" graph at -110dB very close to the primary signal, everything else is below -120dB - including the fact that the "skirting" differentiates only below -120dB... Improvements worth US$10K?

Then there's the second graph:

OMG. That's ugly! Supposedly it's a reflection of the "standard PC" vs. Melco through USB to the Chord Mojo DAC on the 24-bit J-Test. At face value, the first thing this graph tells me is NOT that I should buy the Melco. It's that I should AVOID the Chord Mojo (~US$550)! Seriously, if the difference between the "standard PC" and Melco is so small for the iFi iDSD, what's wrong with the Chord Mojo such that it's so terribly sensitive to noise (not necessarily jitter) that it should give such a result? Especially bad considering this is supposed to be battery powered!

Permit me to make a few (obvious) critiques of these results:

1. We don't know what is a "standard PC". The article says nothing about whether the hardware used is a simple modern i5 laptop, a recent Intel NUC maybe, or some kind of monster i7 CPU with 1000W switching power supply and dual GTX 1080 Ti graphics boards. For all we know this could be an old Mac running Parallels with iTunes in a Windows Vista virtual machine!

2. Related to the above, we know nothing about this "standard PC" playback set-up. Did they use iTunes? foobar? JRiver streaming off the Melco over UPnP? Did they use a toss-away crappy unshielded USB cable (like this one) or something more substantial? Did they even bother using ASIO or WASAPI drivers properly?

3. We also know nothing about the physical layout of the tests... Did they at least take some caution with placing the Chord Mojo a few feet from whatever "standard PC" was used? For all we know, they could have sat the DAC right on top of a beefy switching power supply soaking up the EMI!

Here's my belief... The Chord Mojo is NOT this poor and that 2nd graph either is wrong, mislabeled and/or caught the eye of and put there for effect by an editor who didn't know better. Stereophile's measurements already show us that the Mojo has good low noise and jitter performance; obviously Stereophile did not need a $10K Melco server/player (2012 MacBook Pro). Rather, I think the guys doing the measurements here must have made a mistake. They could have used an unreasonably poor "standard PC" hardware, neglectfully placed the Mojo too close to noisy components, or might have been sending 16-bit data rather than a true 24-bit signal (dithered DirectSound output?), or if streaming to JRiver, they forgot to keep the stream at bit-perfect 24-bits. Another possibility is that there was a ground loop in the system causing noise and hum resulting in that awful noise floor difference. Maybe the dB scale is off between the "standard PC" and Melco? The text descriptions of S/N improvement and reduction in jitter were not this extreme as on the second graph! Something is seriously wrong.

Having said this, IMO, the "evidence" presented in this article is worth considering around the potential of jitter being affected by the computer/server used when connected to an asynchronous DAC. I believe that if HFNRR wanted to seriously convince of the merits of the Melco objectively, they should have been more forthcoming with the hardware used for the PC. Remember that in science, this is important because reliable measurements that can be reproduced independently by others are part of the checks & balances of the process. Unlike subjective commentary, you can't just claim something without clearly informing the reader of the parameters surrounding the test/experiment/measurement. In any event, I'll certainly keep looking when I do measurements to see if I can detect changes as described by this HFNRR article.

The question in my mind though is ultimately this: suppose we accept the findings of the iFi iDSD (like I said, there's something wrong with that Chord Mojo graph so I cannot take that seriously unless verified), do we actually believe the jitter difference is audible with real music? Will a spurious noise spike up to -110dB with the "standard PC" and that "skirting" below -120dB make a difference in the way the subjective reviewer describes what he heard (clarity and focus, bass slam, sense of "drive")? Do we even have many 24-bit recordings with such low noise floors? Let's also not forget that the J-Test artificially stimulates jitter anomalies for testing purposes to show tiny imperfections without making claims as to audibility. (Needless to say, these questions are irrelevant for vinyl lovers due to inherent resolution limitations.)

I know different people will have various perspectives on the questions above... But personally, I'd be very reluctant to believe that human physiology has this type of ability to resolve the difference between a calculated 105ps and 140ps jitter documented for the iFi DAC between their Melco and "standard PC"!

Remember, since the Melco is essentially a low power computer server at its processing heart, IMO they should have shown us what the jitter spectrum looks like with something like an inexpensive Raspberry Pi 3 + external HD enclosure (like this Startech with RAID0 and fan speed control) + dual Samsung 1TB standard SSDs. All that can be built for easily <US$1000. Throw in Volumio or RuneAudio for DLNA/uPnP or piCorePlayer and turn on Logitech Media Server if you prefer. Simply use a decent 6' USB cable. Good luck with measuring the jitter and noise difference between this and the Melco, I think.

The lab report actually stated:

"Ironically, it is the more rudimentary USB hub-powered DAC/ headphone amplifier solutions – as opposed to high-end USB DACs with integral power supplies, etc – that provide us with the best indicator of incoming data integrity and noise (or lack of) on the +5V supply."

What is so ironic about this? If you have to dig into measurements with DACs meant for headphone and battery-powered mobility output in order to show an effect, isn't this good evidence that a device like the Melco makes no difference for actual higher end hi-fi system meant to be experienced in a nice sound room with full-range speaker reproduction? These DACs don't even have balanced output for the lowest noise floor possible (clearly you'd want this with the Melco!).

In summary, any audiophile with $10K to purchase a 2TB low-power computer server should at the very least have the common sense to buy a contemporary Chord DAVE (also about US$10,000) DAC rather than the Chord Mojo :-). They would look fantastic together on the audio rack and together synergize to express the ultimate "non-utilitarian function" of audio hardware as art, furniture, jewelry and of course science. I'm sure we'd all be interested in seeing the jitter differences between a "standard PC", Pi, and Melco feeding the DAVE :-).

** For some more Melco-related audiophilia hysterica, check out their "Software" link. "Purification" of ethernet data with their direct port (!?); they make it sound like accurate data transfer is some kind of difficult thing these days (remember my UDP/TCP test awhile back). Oh yeah, apparently "LAN lights can be disabled for highest possible data integrity" - thanks Melco! No pseudoscience or FUD here. :-) IMO this is shameful considering the respectability and quality of Buffalo's business and consumer NAS products. Perhaps an audiophile hobby where the "mainstream" tolerates this kind of rhetoric deserves to be treated like fools by a computer company selling a souped-up NAS...

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Anyone see new Sonore micro/ultra/Signature Rendu (SE) measurements? I notice that they have a full line-up of devices now featuring all kinds of stuff including various linear power supplies... So, how noisy are these things and any "evidence" like the Melco here of jitter effects with asynchronous DACs?

HFN&RR / Paul Miller / Andrew Everard / Jim Lesurf: Since you guys have already got some measurements with the Melco and "standard PC", why not compare devices? Melco vs. "standard PC" vs. Mac Mini vs. MacBook vs. Raspberry Pi 3 streamer vs. Sonore *Rendu? For the benefit of audiophile consumers, would it not be good to do some investigative journalism independent of device reviews? Would it not be nice to know whether claims are true and to what extent when it comes to jitter with ubiquitous asynchronous USB DACs these days?

Likewise maybe Stereophile would be interested in verifying the results? Again, an independent article exploring measurable differences between devices would be a return to previous form (like this article from a decade back)... For audiophile magazines to provide honest independent explorations into these issues would certainly go a long way to reassure readers that they are not just the advertising arm of the "high end" hardware industry.

Let's be honest though. In 2017 with the decline of news media in general, and perhaps especially with the diminished size of the hi-fi/audiophile hobby, the "bottom line" more than likely is dictated by retention of advertising revenue. Suppose a respected audiophile journalist goes through the science, measurements, controlled listening tests and writes a magazine article concluding that jitter is minimal these days and inaudible. This would take the hype off a certain segment of cable, computer server, streamer, maybe DAC advertisers still trying to convince audiophiles of the "importance" of their jitter performance. Maybe audiophiles will realize they can safely ignore fluff talk about jitter altogether, or more specifically "gee, I don't need a femtoclock upgrade!" Could the current cohort of audiophile magazines tolerate such an outcome? Would such an article ever have a chance to come out in print through the editorial process? What would happen to the reputation of said respected audiophile writer at least within the inner sanctum of the mainstream audiophile press?

Hhhmmmm...

A big "THANK YOU" to those who submitted their results for the MQA Core Decode vs. Hi-Res Audio Blind Test! As promised, I have closed off the online survey yesterday (September 8). In total, there were 83 submissions from around the world (after taking out 2 that were resubmissions)! I do believe this is the largest listening test you're going to find for MQA with any amount of serious attempt at blinding the "subjects"... I have started the process of initial analysis of the data and will present the results over the next little while. Stay tuned - let's see what the data set tells us about audibility and preference of MQA Core encoding/decoding in the real world tested by actual ears/minds in actual home systems...

Enjoy the music everyone!