rb2013
Author of The 6922 Tube Review
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Found this paper [http://pinknoisemag.com/pink-papers/pink-paper-002] independently of @enginedr whilst researching the credentials of my Dangerous Convert-2. It was published January 2016 and, so, is recent. I made notes to help me understand stuff from a low starting point [perhaps I am not the only one - hence reason for sharing]. I have found that an unencumbered PC increases PRaT (and other SQ aspects) extraordinarily and wonder about the "timing" attributes of a system. My chain is [an awesome] PC > D16 AES > Convert-2 [using Convert-2's WC as master]; i.e., no MUTEC [reclocker] nor fancy atomic clock. I suppose aside from academic interest I am playing with expenditure on PC vs. expenditure on reclocker/external clock and/or expenditure on reclocker/external clock per se. Here are subjectively-drawn extracts from the pinknoisemag paper subjectively re-ordered for narrative. I've done this purely for educational purposes (and to indulge my own cognitive dissonance relief strategies wrt the system-balanced money I have invested).
... the pro audio field has witnessed a decade-plus of entrenched disagreement between those who are certain that external clocking can never improve an interface’s performance and those who assert that it can and usually does ...
Previously, master clocks were boring boxes that synchronized various digital devices, but by the middle of the decade the pro audio field had become obsessed with the idea that external master clocks were key ingredients in a digital studio’s sound ...
... As Duke Ellington famously said, “If it sounds good, it is good” – and perhaps a playful reprise for the digital age could be “If it sounds good, it’s probably less jittery.” ... As a rule, systems with less jitter are generally understood to sound better ...
... the [Digidesign] 192s [interfaces] actually did measurably exhibit a marked reduction in jitter when clocked externally. What’s more, when synchronized to different models of clock ... the sonic character of the 192’s output does indeed change. This was why, despite the unavailability of hard evidence to support the notion, so many people began to talk about the sound of clocks.
the ears of experts may be the best, and often the only, “test equipment” we have on hand. Yes, we do mean sighted listening (not double blind tests), and long term immersive listening (rather than short term comparative listening).
How To Listen To Clocks
Below is a list of the sonic qualities that one can listen for when swapping out clocks on a digital system. We generally believe that improvements in any of these dimensions likely indicate a reduction of jitter.
Clarity – Many systems “open up,” exhibiting more sonic detail, especially in the high-end where finer sonic definition resides.
Changes to Soundstage Shape – Some clocks will strengthen the center image and others will appear to widen the stereo image ... One might think of this as the soundstage having a “concave” or “convex” shape.
Front-to-Back Depth – The front-to-back depth of the sonic image can change when swapping clocks, and typically the favored clock will present more depth. Often, along with this increase in depth, is an increase in the detail of reverberated sound within the recording.
Three-Dimensionality – Highly related to soundstage shape and front-to-back depth, three-dimensionality can also be thought of as the relationship of the phantom image in the center of to the rest of the sound stage.
Localization & Individuation – The ability to differentiate and locate individual sounds within the sonic image can often improve when jitter is reduced.
Low-End Focus – The tightness and focus of low end can be affected by an external clock
Low-End Extension
General Ease of Listening – a more relaxed feeling when listening, especially over long periods.
Richness – A highly subjective quality ... We suspect that richness might be the sum total of improvements in many (if not all) of the above characteristics.
We suggest that recordmakers further embrace, rather than shy from, descriptive language, and even look to the vocabularies of audiophiles for linguistic innovations ... Language will always be the material from which we build bridges between the subjective and objective perspectives.
... Not hearing a difference is as valid and important as hearing one, and a key aspect to becoming an expert listener is to not let the opinions of others sway you into hearing things that aren’t there.
The core problem here is that that guided listening can cause confirmation bias (the tendency to seek confirmation of one’s expectations) – a colossal problem in the research sciences. We are not out to convince anyone to take on our sighted listening paradigm as scientific. Instead, we aim to clarify what that paradigm is, and how one might practice and use it.
We Compare Externally Clocked Converters
Externally clocking the Dangerous Music CONVERT-2 – The CONVERT-2 is a stereo DAC that showed no improvement when clocked externally, and in fact sounded a bit worse when it was. This is an indication that the CONVERT-2 is a solidly designed and implemented converter whose internal clock and PLL are expertly tuned to each other. The CONVERT-2 DAC is, therefore, a good candidate as a studio’s master clock and has shown itself to be when clocking converters that do respond to external clocking.
Externally clocking the Burl Mothership –Joel Hamilton told us that his Burl Mothership converters showed no audible improvement when clocked externally to his Antelope 10M system. Thus, he runs his Mothership on the internal clock.
Externally clocking the Lynx Aurora – The Lynx Aurora converters regularly exhibit a sonic change when clocked externally, especially in high-end clarity and openness.
Externally Clocking the Digidesign 192 Digital & Dangerous Music Monitor – As we already know, the Digidesign 192 has been proven to exhibit less jitter when clocked externally. Externally clocking a 192 Digital, and then sending the 192’s AES output to the Dangerous Music Monitor’s DAC revealed the greatest sonic changes from the clocks we tested.
This ... sampling of digital systems should be enough to show how system-specific the role of external clocks is, and why generalizing about them would be fruitless ...
... any combination of clock, converter and/or digital interface forms a unique digital audio system with its own highly specific performance profile, there really is no practical way to predict how any combination of clock, converter and/or interface is going to perform together.
Forming broad conclusions about internal vs. external clocking – or about the efficacy of one specific product, or even about any type of product – is truly a flawed enterprise.
Before recently, there was hardly ever a chance to [We] compare 10 MHz generators. Who had, or could (or would) afford, two different 10 MHz clocks?
Once an audio company has decided on a rubidium core, their job is to implement it into a device that will output the best 10 MHz signal for audio use. Essentially what will define a good 10 MHz design is low phase-noise in the 10MHz sine wave output, which (theoretically) should translate into less jitter in the Word Clock signal being sent to the converter’s PLL.
... all ... 10 MHz clocks improved the sound of our test system
... each 10 MHz generator had such a distinctly different impact on the sound of this system
... Each of these 10 MHz clocks helped to reveal more detail and improved imaging from this system, but in rather different ways.
Impressions of Antelope 10M/OCX – The Antelope 10M/OCX combination brought out so much reverb and widened the soundstage so much ... Other music ... soundstage cinematically wide.
The 10MX was revealed at the Audio Engineering Society (AES) convention in September of 2015 ... The 10MX is the first to house the 10 MHz generator and a Word Clock generator in a single unit for the pro audio market ... The Antelope 10MX provided a wholly different sound than the 10M/OCX combo. The individuation of elements was crystal clear, details firmly localized, and reverbs were far less enveloping and washy. The soundstage was wide, yet the center image was strong and present, so the sense of width was not quite as enhanced as with the 10M/OCX.
Impressions of the Stanford Research Systems PERF10 – very different sound ... whole extra low octave ... consistently brought the bass like no other 10 MHz combination we tried.
Conclusion About These 10 MHz Clocks – As we will show in the next section, we can not grasp why one would invest in a 10 MHz clock for audio, but if for some reason someone felt they had to, we would point them toward the Stanford Research System PERF-10 as the less expensive and more enjoyable option.
For audio purposes the concern is for short-term stability, as we want our zeros and ones to be delivered as evenly in time as possible, while the accuracy of the signal in 1000 years is of no concern ... despite the fact that long-term accuracy doesn’t matter for audio – atomic clocks have made quite a buzz in both the audiophile and pro audio markets ... a breed of clocks emerged that use rubidium osciallators to discipline the crystals into having good long-term stability ... in 2008 Antelope Audio released the first 10 MHz clock aimed at the pro audio market ... the era of aesthetic external clocking was in full swing ... it is important that we carry you through an elaborate sighted listening process as well as some refined logic that deals with how 10 MHz technology was able to have been taken seriously by the audio community despite it being a ruse.
We compare 10 MHz & Crystal Clocks
Using the same jitter-revealing test system, we were curious to learn whether there was any obvious advantage to these 10 MHz clocks over crystal clocks, so we took what we had on hand and did a comparison of crystal clocks to the SRS PERF-10/OCX combination (our preferred 10 MHz rig).
Antelope OCX as Master Clock – As we mentioned earlier, the OCX on its own did not reveal the kind of high-end detail, nor the width and depth as it did when driven by a 10 MHz generator (especially the SRS PERF-10). However, the low end on the OCX was more powerful than with the Antelope 10M hooked up, and the center image was more pronounced. Generally, however, the overall sonic image was not as engaging, and the center image strength was at the expense of detail and interest in the left-right sides of the stereo image. The sound was disorganized.
Cranesong HEDD 192 as Master Clock – Wow. Delays and reverbs that were nearly inaudible with the Antelope and the TASCAM were obvious and lush with the HEDD as master clock. The depth of the soundstage was vast. All around the HEDD’s clock provided a much more professional sound with a strong center image. Localization was excellent. Low end balanced and punchy. A much more 3-dimensional listening experience all around. The HEDD was our favorite master clock on this rig.
Forssell MADA-2 as Master Clock – A second “wow” for the Forssell. This clock was similar to the Cranesong HEDD in its revelation of reverbs and delays. Localization and individuation was stable and precise. Width was pronounced, perhaps slightly at the expense of the center image. Low-end frequencies, while full-bodied, were not as clear as with the HEDD.
Was the Cranesong HEDD Better Than the 10 MHz Clocks? – Yes. From the crystal oscillators we had on hand for our initial listening tests, we honed in on the Cranesong HEDD as our favored crystal clock for this system (with the Forssell as as very close rival). We then returned to the 10 MHz clocks and compared. We quickly zeroed back in on the Stanford Research Systems PERF-10 as our preferred 10 MHz clock and did a comparison with the HEDD.
We’ve described the sound of these clocks above – however, the biggest differences between the HEDD and the PERF-10/OCX combination was that the HEDD delivered articulate and dynamic front-to-back depth compared to the PERF-10/OCX combination. The sonic image when using the HEDD reached into the room while still presenting reverb and delay details that reached far back into the space behind the speakers. It was a very three-dimensional and engaging soundstage. Low-end on the HEDD wasn’t quite as big as the PERF-10, though it was more clear and dynamic in general, with better note differentiation and detail.
Grimm Audio CC1 and Dangerous Music CONVERT-2 as master clocks.
Grimm Audio CC1 Master Clock – This clock is incredible. The detail and imaging from it are superior to anything we heard, and the overall “relaxed” sound of the playback was as close to analog tape (read: jitter-free) as anything we’d tried. The Grimm CC1 didn’t make the music sound as aggressive and forward as the Antelope clocks, and that was a huge plus, because what you get instead is unparalleled depth and detail, as well as a feeling of “calm” that none of the other clocks provided.
Dangerous Music CONVERT-2 as Master Clock – The CONVERT-2, a dedicated D/A converter, provided great sound from the system when used as the master clock. The level of detail wasn’t quite as crystal clear as the HEDD, but there was an “analog quality” to the sound that was appealing. Reverb depth was particularly good. Like all the other converters-running-as master-clocks that we tried, the CONVERT-2 could provide a great master clock in a studio that needs a high-end D/A as well and doesn’t have the budget for a dedicated external clock like the Grimm.
Listening and Logic Agree: 10 MHz Clocking for Audio is a Ruse
In the absence of jitter measurements (for now), we are left with listening and logic. In the case of 10 MHz clocks, logic and listening are aligned.
We’ve shown above that on our test system the 10 MHz clocks, while capable, were not able to outperform the crystal oscillators found in two high-end converters.
As we explained above, for audio we are interested only in short-term stability in a clock. The rubidium oscillator is an elaborate and relatively expensive device that improves long-term stability. So, the logical conclusion – and one that lines up with our listening evaluations – is that nothing is gained from adding a rubidium stabilization device to a crystal oscillator for audio use.
... unless you’re using our test system, you’re going to have to go and do these tests yourself on your system. The specific products that we tried – as well as products that we hope to try in the future – are all going to work differently together. We will not generalize on your behalf.
From a consumer’s point of view, if you run the cost on all of the clocking options we’ve presented so far, you can see readily that an excellent two-channel converter [cf. Dangerous Convert-2] can also make an excellent master clock. Dollar for dollar, using a high-end converter as your master clock is an excellent solution for mixing and tracking engineers who need great sound from dozens of channels of AD and DA systems that show reduced jitter when externally clocked. Along with great clocking, you also get two channels of excellent conversion. Once you add up the expense of a 10 MHz clock rig, it’s difficult to see why anyone would spend that kind of money on a system that has mostly won favor by way of a ruse (however intentional or unintentional that ruse may have been).
Dropping The Digital Ideal – Toward Multiple Transparencies
Given the variability of sound that we heard from all the different clocks and converters we’ve tried, we believe it’s time to move away from the tired notion digital audio is evolving toward some ideally transparent system and to embrace that a diverse array of beautifully executed converters – all of which will have “a sound” of some kind – is emerging. Transparency and musicality (this means ‘beauty’ we believe) will always be intertwined in an elaborate and confusing dance between the speakers.
May I please refer any requirement for clarity or expansion to the original paper!
Good stuff! This article shows that clocks do matter and sound different - as amazing as that is.
I would say much depends on system synergies. The weak link in all this Pro Audio gear (Rednet. Mutec, Antelope, BURL, GRIMM?, Dangerous?, Cranesong?, Forsell?) - are the use of cheap SMPS's. The power supply in the Rednet's for example are said to be $1.80 Ferex units with 150,000 uV RMS of noise!
Some on Tri-Ni-Na have modded the Mutec's PS to external LPS's
To good effect - here is the stock SMPS:
I found the Antelope OCX really made a difference as an ext WClock on the Rednet 3 - many have commented on the better Antelope Live Clock as improving the SQ.
The OCX has a SMPS - the Live Clock has the ability to use an external DC LPS
That is something I would explore if I owned one.
I found the BURL B2B DAC was helped with the OCX - before the power supply mods. Now running on a decent LPS - the ext Wclock made no improvement, in fact it hurt the SQ.
So the PS on all these units are very important.
Someone had posted on the Rednet that they had modded it - to run on an external LPS - but not much detail there.
This new AOIP full DANTE unit I posted about looks very interesting - DC external power and AES XLR sockets (the advantage of the RN D16AES over the 3).
Another feature of the Antelope Live Clock is the ability to recalibrate it's crystal clock to an external atomic clock. All clocks drift over time away from their reference freq - XO and TXCO more then Rubidums - by orders of magnitude. The totl Crystek CCHD-975's quote 3ppm in the first yr, then 1ppm each year there after. The Antelope Live Clock: 1ppm per yr. The SRS PERF10: 5ppb per year, . Does this 1000 times more stable clock matter? After 5 yrs the 975 has drifted 7ppm vs 25ppb for the PERF10. Since clocking is the heart of digital audio - maybe this long term drift does matter?
With the Antelope Live Clock you can have the clocks recalibrated yearly to an atomic clock - nice if you have a rich friend!
The big issue with all these super clocks is the cost. I'd rather explore the more important power supply issues.