I like the idea of Ted at dCS, though I suspect it’s unlikely. On a bang-for-buck basis, I think PS Audio produces excellently performing and high value equipment. I’ve owned a lot of their stuff. Quite musical.
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Hmmm. Before getting the Cybershaft OP-21A, I had pulled the trigger on both an SRS Perf10 and an Antelope 10MX rubidium clock. The latter’s studio capabilities scared me off a bit, and I knew less then than I do now. Among other things, I had “over-interpreted” the notion that atomic clocks are generally bad for audio devices. I am inclined to give both a try, and see how they compare to the Cybershaft. Their long-term specs seem to me to meet James’ threshold requirement, although I may be interpreting them incorrectly.
The idea that atomic clocks are bad for audio does have some basis, but it depends heavily on where they are used. Because the short term accuracy (the area that is important for audio) of an atomic clock is pretty low comparatively (jitter is created while the clock tunes itself around the target frequency), it would generally be a bad idea to connect it directly to a DAC for example. It will essentially be a jittery signal, at least by high-end audio standards.
However, while the signal is jittery, in the long term it will be incredibly accurate as all the tuning around the target frequency will average out over time. So, feeding it into a second Master Clock with a quartz oscillator (which have inherently low levels of phase noise and jitter) provides this second Master Clock with a long-term stable reference to adjust to.
This of course depends on how the PLL in that second Master Clock has been designed - if it has a wide bandwidth (is fast acting) the jitter may well be passed on to the DAC. If it has a lower bandwidth PLL (slower acting) the jitter should be filtered out before it reaches the DAC, mitigating the issue. For reference, the PLLs in a dCS DAC or Clock are the latter, being slower acting.
So, are they bad for audio? Really depends on where in the chain they are used, and how the products it connects to use the clock signal.
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Thanks for that @James. Very helpful. And consistent with the earlier info you and @Anupc have posted here and elsewhere. I’ve got an SRS Perf10 on the way, and I am in the process of trying to borrow an Antelope 10MX. The Perf10 claims a long term accuracy of ±0.05 ppb ( ±5 × 10-11), and they also assert they have optimized short term phase noise for audio purposes (though, as you note, the Vivaldi Master Clock is less sensitive to this noise in a reference clock). Esoteric sources the same oscillator from SRS for their Grandioso G1 Clock. It will be interesting to see what, if anything, I hear. My experience with the Vivaldi Clock and the Cybershaft is that the changes are holistic, and not identifiable in traditional audiophool terms. But the change was readily apparent.
Maybe a cesium clock in the Vivaldi successor stack? 
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This last paragraph reminded me of something you wrote in that post that Pete linked above:
From the perspective of a reference clock connected to the dCS Master Clock on a 10mHz input, is this rate multiplication a factor, and does it occur in the reference clock or the dCS Master? Forgive my ignorance; I am just trying to gain a layman’s appreciation for all this. Let’s posit a reference clock of cesium accuracy [I know, not likely for any of us here, except maybe @Anupc 
], with acceptable short term specs as well. Presumably, such a reference clock can “enhance” the dCS Master Clock’s accuracy, yes? No? Maybe?
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Yes, in so much as the 10MHz signal still needs to be synthesized into something the dCS Master Clock can actually use for its own purposes (audio) which involves going between mathematically unrelated rates. Asynchronous rate converters typically equal a dirtier clock spectrum, which means jitter.
In the dCS Master. Using your example of a cesium clock, this will only operates in the 10MHz domain, so it is up to whatever it attaches to (in this case a clock for audio) to synthesize that into the relevant rates.
If the long-term accuracy was higher than ±0.1 PPM, so with the clock above you mentioned with the long-term accuracy of ±0.05 PPB yes you would likely hear an improvement. Note that this doesn’t have any impact on jitter performance, which is short-term accuracy (think looking at one rising edge of a clock signal next to another on a 'scope, whereas long-term accuracy could be over a period of an hour seeing how far one clock signal has drifted from the other).
Again just to reiterate because of the fact the PLL in the dCS Master Clock is slow acting, the short-term accuracy of the reference clock isn’t too important (if it was, an atomic clock would degrade the sound), it’s mainly the long-term accuracy that is the key factor.
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@James, can you elaborate a bit more on how long term clock accuracy matters for audio? Most of the material I’ve read indicates that it’s not very important, as for the duration of say one song the clock skew between even a cheap quartz osciallator and an atomic clock is barely measureable. Intuitively this makes a lot of sense, so what’s being missed here?
I do understand what you’re saying about short term stability mattering less for the slower acting PLL in the Vivaldi. This does however seem to indicate that spending big bucks on a Cybershaft clock that’s optimized for excellent short term stability may not achieve what buyers hope for with a Vivaldi!
Jeff, just the point I made over at WBF over the weekend, and why I am eager to get the SRS Perf10 in to see if I can discern any difference. I am looking forward to @James‘ response, perhaps with some additional detail on the role of dither. Suppose, let’s say, the Cybershaft on paper is more accurate/stable in the short term than the Vivaldi. Is it possible this improves the Vivaldi, and if so, is it likely to be audible? We know our hearing is sensitive to timing, but are we now at a point where incremental improvement may not be discernible? Even if something like the Cybershaft could enhance the Vivaldi’s short term accuracy, does the dither option negate or work at cross purposes? Given the design of the Vivaldi, does adding a more short-term accurate clock simply not do anything? I.e., for practical purposes, is there truly no way to improve the Vivaldi’s timing accuracy in an audibly meaningful way?
Scientifically, I am out of my depth here, but I would love to get to a better cognitive understanding of why and how the Vivaldi might be improved other than the sense of openness and space emanating from the cavernous hole in my wallet.
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Greg, it’s a very intersting topic!
One other variable that’s not well specified is how good the Cybershaft long term stability is. It’s possible that it’s also an improvement over the Vivialdi clock, so if that does indeed matter that could be what people are hearing. Cybershaft doesn’t specify this, but they do use aged clocks that have supposedly stabilized.
This also ties into the idea of removing the Vivaldi clock from the chain entirely and replacing it with something like the Sound Warrior that converts the Cybershaft to 44/48 Hz with minimal phase noise degredation. Of course if the DAC/Upsampler also use the lower bandwidth PLL, then maybe we’re back to square one again!
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Well, the Vivaldi has to do this as well, correct? I mean, there is no avoiding this step, is there? I see the economic advantages of the Sound Warrior [!], but do we have user reports of an SQ comparison? Other than economics, is there a reason to believe the Sound Warrior is a better match for the Vivaldi DAC than the Vivaldi Clock?
P.S. I will dig up my OP21A spec sheet and see if it says anything about long term stability. I don’t think it does.
That’s actually a really good question. You’re right, absolute accuracy has much less of an impact on sound quality than jitter performance. Put another way, I believe the discrepancy on middle C worldwide is around 60,000 PPM, so we’re working at accuracies well above that as it is. Being perfectly frank, given this personally I do not have a solid explanation for why an incredibly accurate long-term clock would provide a sound quality increase.
With that being said, we’ve had reports from customers over the years who have done tests with different reference clocks going into a Vivaldi Clock. Invariably from a few who (I believe) were doing blind tests, they all independently concluded that an atomic clock with a very high long-term accuracy offered an improvement in sound quality. Obviously one clock’s long term accuracy being higher than another’s shouldn’t in itself offer a substantial increase in sound quality given our low psychoacoustic sensitivity to long term accuracy (as a whole the human ear and brain is much more sensitive to short term timing errors than long term frequency drift caused by long term inaccuracy).
I must admit that running an atomic clock into a Vivaldi Clock isn’t something I have had the opportunity to try personally, but the consensus seems to be it does offer an improvement. I should note that unlike some other “does it doesn’t it” topics floating around the audiophile world, this one is whether the human ear is sensitive enough to hear the difference, not whether the difference exists.
A clock directly feeding a DAC has a very different requirement to a clock feeding another master clock though, so obviously the relevant specs in each and how they should be taken into consideration across the whole system will differ. Absolute accuracy into a DAC is a different ball game to absolute accuracy into a Master Clock.
I try to stay away from inter-manufacturer debates and instead discuss the technology and engineering principals. I would say though that we have been in the Master Clock game for several decades now, and go to some impressive lengths to get the best jitter performance possible. We also have pretty much free-reign to create an audio system which is the highest performance possible, and with that over three decades we have settled on the FPGA enhanced VCXO system, with some incredibly capable PLLs throughout the system. The whole Vivaldi system has been designed to sound as good as is possible, period, with all the trade-offs that entails (there’s no such thing as “compromise free” in engineering, engineering is compromise), as opposed to something that’s good on paper.
In short, no, dither won’t impact an external reference clock’s effect on a Vivaldi Clock. The key point it impacts is the DAC’s ability to lock to the incoming Word Clock signal from the attached Master Clock when the phase difference between the two is low (somewhere PLLs naturally exhibit a dead-zone). It’s one of the ways the dCS system as a whole minimises jitter, but operates only within the dCS ecosystem and wouldn’t be impacted by an external reference clock.
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Most excellent info. Thanks very much @James.
Let the experiments begin! The Perf10 arrives tomorrow (Tues), and I hope to get it installed by evening.
UPDATE: Perf10 arrived, unboxed, and installed. Piece of cake, just like the Cybershaft. Vivaldi Clock locked on immediately, as soon as the short warm-up period completed. The unit has an unfortunate surfeit of unnecessary bright LEDs, it’s very utilitarian, and its rack-mount ears are not removable. But that’s it for the negatives. I made detailed notes from reference test tracks and cuts I know less well, before disconnecting the Cybershaft. I plan to keep the Perf10 connected for another week for casual listening, and then disconnect it from the Vivaldi Clock for some serious no-reference-clock listening and note comparison. After a week like that, I will reconnect the Perf10 to the Vivaldi for more comparison listening.
By the time I am done with all that, maybe dCS will have released the Vivaldi successor stack with an OCXO clock and satellite-linked cesium correction. Can’t let CH Precision have all the fun.
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I hope you post a progress report at least. I don’t think that I can wait for as long as you anticipate your comparisons will take. Mind you what should I care? I have no space to put it even if you tell me that it exceeds all expectations 
Thinks; maybe stick some neutral plastic light filter sheet over those bright lights?
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Hey Pete. Those lights have already received the black electrical tape treatment. Only takes a small slice to cover them. More impressions to come, I am sure.
Not sure if anyone else here has seen the only detailed review of the SRS Perf10 out there. I think the reviewer unintentionally reveals his lack of understanding of how the Perf10 works, even though there is a fair bit of interesting detail. And his conclusion comparisons against the Grandioso and Vivaldi clocks suggest further to me that he is comparing apples and oranges.
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Greg, I agree with you about the possible lack of understanding by the reviewer of exactly what is going on. However in his favour he mentions the existence from the same manufacturer of a half case sized alternative without so many LEDs intended for lab use. I really wish he hadn’t 
.
BTW he mentions the rumour that the basic clock from Stanford Research is sold to makers of other far more costly rubidium clocks intended for audio purposes. This is what I heard about that incredibly costly one that I heard coupled to a Vivaldi system last year ( see archives).
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Yes, Pete, I was not going to mention that lower cost alternative for fear of tempting you. Fear not, though, I am not sure it is quite a “drop-in” substitute. I took a look at the user manual, and it was enough to convince me to stick with the Perf10.
And in a different review, he confirms that Esoteric puts the SRS oscillator in their Grandioso G1 clock.
As to mistaken comparison, just to be clear, the SRS is a functional competitor to the Esoteric Grandioso G1 and the CH Precision T1 as a Reference clock. Whatever it’s plugged in to must accept a 10mHz signal like the Esoteric equipment he tested for the review. The Vivaldi Clock is not functionally equivalent. But just as is often said here, my guess is that Esoteric and CHP equipment are optimized for each other. In a sense, the SRS is a “generic” piece of equipment that can be plugged into any 10mHz-receptive device (the SRS data sheet specifically mentions dCS and Antelope). One should expect that the Esoteric and CHP at roughly 8-10x the cost should sound as if they were optimized for their intended use.
The fact that SRS might get someone within striking distance of such sound is, as the reviewer notes, a remarkable achievement. For someone who wants to ratchet up their CHP or Esoteric stack, but is stymied by the high prices (are there such buyers?), it’s an amazing bargain. And for dCS users, it’s an even better, but different sort of bargain—assuming for the sake of discussion that one has a system and ears to hear the difference—because it adds that last bit of timing accuracy at an incrementally “reasonable” cost to the amazing Vivaldi stack.
P.S. I am not going to say the Perf10 made an immediate difference in my system. But sitting here listening to the SACD rip of Muddy Waters’ Folk Singer, it did.
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Greg, it’s not the cost, it’s the size. Mind you, to be honest, even with a half size case I still don’t have the room. I would if I didn’t also run a serious vinyl system. However I have several thousand LPs which reflect my musical interests over 55 years and they are staying 
.
My apologies. I remember you have mentioned the space constraint before. Those LPs—you’re such a hopeless romantic.