[art]

Introduction

Some of you may be aware that after a 3-year hiatus, we are starting to build equipment again. I could write a tome on what went on in those years, and why it took so long, and why it was a mess (a lot of which was out of my, and seemingly anyone's control), but that isn't the point. The point is the only stuff that was not boxed up and stored away was all of our gear to measure phase noise. Not that I needed any practice, as this is what I did, back when I had a "real job". So, this is not some new fascination with me. Since I did have an extensive background in this stuff, not to mention we now have gear that doesn't take up an entire 6' rack*, it was a way to keep the doors open. All we needed was a small testing gizmo, an external frequency reference, some test jigs, and something to measure. Which I did.

During that time, I have measured hundred of these teeny-tiny little clock parts. We sold tested and sorted ones to various manufacturers. We also worked with some of the largest companies around, that make "frequency control products", to help them refine products they intended to bring to market. We tested lots of samples, that other "high-end" companies (and some Pro Audio ones as well) were interested in using in their products.

It is important to understand some of these obscure matters before we get started. There are also some technical matters that need some background, and that will be the next post. So, let's get started!

* = Ironically, even though HP/Agilent/whatevertheyaretoday makes a phase noise gizmo that can sit on a desk, it still costs around $90k! Just like it did back in the 70s and 80s, when it took up an entire rack. How can that be? Lucky for us, there are affordable knock-offs. Limited in what they can do, but still very powerful gizmos.

[art]

OK, so what is jitter?

Well, there are 2 ways of looking at it. One is in the time domain, and the other is in the frequency domain.

To some of us, it seems that folks who do "digital" design only look at the time-domain element. Meaning how much a clock signal causes the data to be shifted, back and forth, relative to when it is supposed to happen. In turn, they might accuse those of us who look at the frequency domain don't understand what jitter is all about.

Let me answer that with this anecdote..................

At my last "real job", there was an infamous incident where I threw a VP of our company out of my office, for snidely asserting that I needed to get some education on how digital stuff worked. All that you need to know is that I was not fired, and he never got in my face again. (Yes, actual event. But, it should not surprise anyone I had a history of taking on upper management, and never lost my job. Hard to fire someone who got results. Results that paid their salary.)

Ok, now that you know where I stand, let's start looking at how jitter is measured.

First, I would like "you guys" to read this link:

http://www.rakon.com/component/docman/doc_download/225-phase-noise-and-jitter-in-crystal-oscillators?Itemid=

Once you read it, some of what I am going to bring up will make some sense. You will not have to memorize all of it. Just get a rough overview of what they are explaining.

Such as:

This can be analysed by matching the slopes of the real Phase Noise plot to those
shown in the idealised Phase Noise plot of Fig. 9.

For this particular plot:-
Flicker corner of Buffer Stage ~ 5 kHz
Loaded Q of the Crystal ~ 170 Hz (Q ~ 38k)
Flicker corner of Oscillator Transistor ~ 12 Hz
Random Walk ~ 0.1 Hz (extrapolated)

Two things to take from this:

1.) Phase noise ("jitter" measured in the frequency domain) has lots of components. It isn't some number some gizmo spits out. Numbers, without context and understanding are just numbers. And, when it comes to jitter, pretty much meaningless, without any context.

In the case of "jitter", the context has to be the frequency range over which the jitter is measured. And there is the problem. Because what that range is must be defined before you know whether or not something is "low jitter" or not. (More on this in a bit.)

2.) See that odd reference...................."random walk ~ 0.1 Hz (extrapolated)"?

Let's talk about that, because we are going to see a lot of that, in the plots I am going to post.

Let me just interrupt things to say if you are going to come here to argue and tell me nothing below 20 Hz or 1 Hz or whatever Hz is audible, and I don't know what I am talking about and this is all a waste of time, etc., etc., and more etc., then just stay out of the discussion. I have heard all of that crap so many times I can not stand to hear any more of it. So, do us all a favor and go watch "March Madness", and not make a mess of this. (Asking questions is ok, because you are all going to have questions, and if I was not willing to field questions you would not be seeing any of this. But stirring up crap, because it exposes your ignorance is not my problem, is not going to anything I will address.)

So, assuming "you guys" have looked at that plot, you will notice the phase noise plot stops at 10 Hz. Why? Well, for the obvious reason! It is easier, faster (and therefore cheaper) to not go below 10 Hz. Not because what goes on down below it doesn't matter. It is because it is a pain.

Now, if you have lots of time on your hands (because everything else is boxed up), so what if it takes a lot of time? Besides, all of those years spent previously measuring this stuff, you know how it important it really is.

Even the folks who do not measure below 10 Hz know it is important. A certain company that makes "frequency control products" worked with us so that they could find a correlation between their 10 Hz measurements and our 1 Hz measurements. It just takes too long for them to do it, but I can assure you that they are very interested. Granted, 99.9999% of their customers won't care. But, they wanted to make some inroads into making clocks that would be really good for digital audio. Which is a balancing act. Cell phones are  driving that market. So, if it does sound better, there will be a market for it. But, it has to be as cheap as the products that stink. Which is tough to do. (In this case, the plan was to find a way to tweak their existing process, to make a specialty product, with higher price, obviously, that would appeal to our segment of the industry. Turns out there is not just one knob to turn, to crank out those better parts. Which is why it became an on-and-off-again endeavor.)

So...............if you don't measure below 10 Hz, then how do you know the "random walk" kicks in around 0.1 Hz?

Experience.

Or so I thought.........................

We'll see this in the plots. But, before that...................more background stuff.

[art]

OK, more background........................

The guys who make "frequency control products" all have the same way to publish their "jitter" specs.

Jitter frequency measured with f>1 kHz.

What does this mean?

Well, they only measure jitter that exists from 1 kHz and up.

Why?

Because 1.) it is easy and cheap to do, and 2.) it makes for a very low number, and therefore the weenies in the purchasing department (not to mention brain-dead engineering management, who only go into management since they were crappy engineers) all think they are buying a quality product. And if the people that work for them are just as ignorant...................

You get the idea.

But, what is in that f>1 kHz jitter?


Look at the phase noise plots, in that link I suggested that you all read. (You did look at it right? It isn't that long.) What is it?

[Thermal noise (Johnson noise)
i.e. kT buffer amplifier noise, resistor noise and Shott noise.

IOW, the noise floor. Has nothing to do with the crystal.

"So, if it is independent of the crystal, why do they even spec it?"

See above.

You will note that the really good parts will have a table of the actual phase noise. Most do not go below 1 kHz. Some will go down to 10 Hz. You have to look very hard for one that goes down to 1 Hz, but they do exist.

So, here is the latest spec sheet, for a part that we use. I have to note that this is the latest and greatest, right on their site. I say this because for several years there was one that showed a ridiculously low phase noise plot.

Well...................sort of............

Sort of because some will actually do those ridiculously low phase noise numbers. And folks believed they all would! (HA!) The truth is they are really more like what they are now showing on their site.

https://www.ndk.com/en/ad/2013/001/index.html

(The one we are talking about is the SPXO.) (Yes, the other one is pretty darn good. And look at how big the package is, and all the mess it will be to mount one in a product!)

Let's see where was I..........................uh.......... ........oh, yeah, the "published" vs "real world" specs.

So, in the case of this one part (that we sell sorted versions to folks who can afford them), there is a certain amount of them that will really do what the supposedly real spec sheet says. (Wish I could find a copy of it. Well, take my word for it. It does exist. I may have copy. And no, most do not even come close.)

Now the ones that do not come close.......................if one were to only measure the phase noise (or "jitter" above 1 kHz, they would all measure fantastic! But, a lot don't. We have hundreds of them that are not good enough. (We may sell them, some day, in lots of 25 or 50 or whatever, for next to nothing on ebay. Maybe. Maybe not.)

OK, time to split this up, and talk about the jitter number problem..............

[art]

OK, the jitter number problem....................

As you should have garnered by now that the are lots of components in the jitter. And this is just from the clock! Yes, there are other sources, mostly crap on the supply voltages, from all the dividers, multiplexers, etc., etc., etc. And, in the case of good ol' SPDIF, you have all the sub-code crap.

"Why do people still use that crap? What good is it?"

You can transmit it longer than 12', which is what USB can do.

"Yeah, but now you can do LAN or wireless."

Yes, but none of that is the point. The point is you have essentially 2 sources of jitter: the clock and all the other crap that creates noise on the power and/or ground lines. I only mention SPDIF because you can see all the crap it creates, very easily, in the "modern" methods of measuring "jitter". And being able to point out the crap is essentially the point of "modern" jitter numbers.

If you are willing to accept that jitter is some number, that is undefined, and comes from some computer-controlled gizmo that reads what goes into a sound card, and spits out some plot that has a magical number attached to it.

Not saying that number, as ill-defined as it is, doesn't contain useful information. It does. It just presents a very incomplete picture of what the jitter really is.

Because it can not measure all that "close-in" jitter. You know, the phase noise that is less than 10 Hz in frequency offset. It wasn't designed to do that, and it can not do that. The only way to do that is to actually measure the clock itself.

Look, if you want to believe that the clock is not important, and only the internally-generated crap is relevant, well it is a free country. But, if you don't want to know what goes on below 10 Hz or so, because "it can't be audible", then why measure anything. (I'm guessing because you have found a way to make your "jitter number" look better than the next guy's "jitter number" and that is all that you really care about.)

Fine. It is a free country. We are glad that 99.99% of the industry doesn't believe us, because there is no way we could supply parts to them all. (Although that would be a really interesting problem to have.)

So, for the rest of you........................on to the fun and games! Background complete.

[art]

So, here is a phase noise plot of some gizmo we are starting to build. Which maybe no will will ever buy, but so what?



"What the.................................? What is all that crap? I can not make any sense out of it. And what does 'DIY' supposed to mean? I'm confused."

So, was I, when I first powered this thing up.

Remember that part of "random walk ~ 0.1 Hz"? You know, where it usually is, 99.9999% of the time. So, why the ^$^&$+Y#YU#***#^$ is it around 5 Hz?

I have no idea.

"I thought that you said that you have measured hundreds of these things. Are you are just now finding out they stink?"

I have. And a lot do stink. But all were measured in a test fixture, in a controlled environment.

But what the..................and what does the "DIY bit mean?

Simple. It was measured the way a lot of "DIYers' might build something. You know, they build it, and listen to it. And that is that.

"OK...............and manufacturers do something differently? I'm so confused."

(Don't worry about that last part, ok.)

Well, maybe that isn't 100% true. There are manufacturers that make gizmos that are part of something else, which might be a computer or built into something else or will be used with something that is used with something.........................iow, not a big fancy metal box that looks all shiny that you can show off to your non-audiophile buddies (so they can wonder what it is with your obsession) but instead is just something sitting there. Calling that "DIY style.

(At this point, a thought comes to mind. We have sold these clock parts to some places that make these kind of computer thingie gizmos. Yet, they never re-order. I think I now know why....................................)

So, at this point, you ask how do I know it is "random walk"?

Uh, because I know what random walk looks like, even if it takes place a 5 Hz instead of 0.1 Hz, like it should. (Why? I would be lying if I had the slightest idea. Ok, maybe I really am an idiot!)

Or, because I fixed it, the way I normally fix it. So, at that point we go from the top plot (oh, good grief, that is horrible!), to the second one, which looks pretty good.

"But what does any of this matter to any of us? It is just some plot. You know what it means, but so what? Does it have any real significance to anything we care about?"

Yes, of course it does! If it didn't none of us would be here.

Now to the even better stuff.....................(I promise)

So, a lot of you should be wondering does any of this tell us anything about how it will sound?

YES!

OK, forget about all the crap above 1 kHz. Not only because I have explained how the noise floor is not important, but because this is a "budget" product, there is no test point to directly measure the clock. I have to measure the output, and let the s/w manipulate everything, to know what the clock is doing. (IOW, all that exists above 1 kHz is pure garbage. In fact, there is a TON of SPDIF crap above 10 Hz, as well. The s/w has a way of ignoring that, if you tell it do that.)

Well, since all of them have good phase noise, down around 10 Hz, I can safely say they will have a clean top end and tight bass. IOW, a lot of the "digititis" will be gone. But, it still won't sound right. (How exactly, I can not say, as I have never seen random walk that high. Let's skip over that, for now, ok?)

So, if you look at the bottom plot, the one that is what the finished product will look (and sound) like, you will see there is no significant amount of random walk. You will recall, from post #1 that random walk increases at 40 dB/decade and the f^-3 noise increases at 30 dB/decade, we are still in that part of the curve.

Which will lead me to state, with 100% certainty...........

Once you get rid of all of that random walk crap, this unit will sound as good as any "analog" system. IOW, not only will the bass be tight, the top end will be clean, and free of grit and glare, but this unit will actually produce a "3-D sound stage".

How do I know this? Lots of testing clocks, and just as much listening to various ones, and making notes, to correlate measured phase noise to sound perception.

Since we consider this research to be proprietary, I am not going into details how we did it. Accept it or reject it, your choice.

Same thing goes for how we fix the random walk problem. Sorry, guys.

Seriously, if I told you how we fix it, this would turn into the biggest food fight on any forum, possibly ever. If you think the stuff we have said in the past is controversial, well this one takes the cake.

Most would not believe us, and therefore call us liars. Some would try it, and it wouldn't do diddly-squat, because unless you have clock that has a phase noise number, below a certain level, well the easiest way to explain it is the inherent noise will swamp any random walk noise. you simply must have good clock in order for the elimination of the random walk to matter.

Anyway, maybe we can at least all agree if you only measure what goes on above 1 kHz..................

(Do any of you guys honestly think all 3 versions sound alike? If you do, well............not much to talk about, right?)

Next..................another new crappy thing we are building, and does it do the same stupid thing!

Stay tuned. Or not.

[art]

Oh, I forgot something!

This may give you guys some clues. Or not!

Here is what the frequency difference looks like, for the 3 versions. Notice which one looks the most stable?

(Don't ask what "linear residual" is. This isn't a class on regression theory. Not that I would even understand it............................)



"I thought that you said drift doesn't matter, last week or so, in some other thread?"

Well, yes, but this is not necessarily "drift".

Remember the old days of "wow" and "flutter". Kinda sorta the same thing. Only different.

Different in the range that they exist under. Same thing here. This is too fast to be considered drift. Trust me, ok?

Enjoy!

Back in a while....................

[art]

One more thing that I forgot..................(don't ever get old)................

You will notice in the second plot it states that the jitter was measured between 1 Hz and 1 kHz. Can't measure above 1 kHz, in this example, as previously stated. In the next set.......................we are going to be brave and measure all the way out to 100 kHz! Hotcha.

[art]

Ok, as promised..................some other POC that we make. Since this is a bit more expensive, it has a test spigot, so I can measure the clock directly. And, since some folks are really concerned about what goes on at 100 kHz offset and how the jitter numbers are different, etc., we are going to go out that far.



Well. Several things are obvious. I think.

Going out to 100 kHz means little, if anything.

These clock parts are not happy, without "the fix".

And.....................wait a second..................what happened to the simple fix, and what is this "extra fix"?

Well, I reversed the order that they were applied in.

"Uh, I am so confused now..................I have no idea what you are talking about."

Don't worry...............a lot of folks are convinced none of us here know what we are talking about!

So, here is what happened, and for a reason.

I actually measured this one first. And I thought it was broken! (Could be..............new PCB design, untested..............who knows, right?) So, I did what would essentially be the final version, for the right way. Then, I added "the extra". As  you can see, the "extra" really doesn't help any.

But......................

if you can not do it the "right way" and all that you can do is the "simple fix", then these parts really need it. But, it still needs help, so just do it the right way, unless there is no way to do it.

No more clues! (Go ahead..............hate us................we're used to it.)

OK..............and just to show that you just need to do it the "right way", here is that weird frequency difference plot:



See, it works the right way, and doesn't need any help.

But just in case someone goes mucking around the inside of one of these................the extra, just in case!

Ok, all for now. Coming up (in a day or so).................what happens if you measure one of these at 22 MHz, and let the s/w divide it down to 11 MHz, or you one of those nasty flip-flops to do the divide by 2 in the test fixture. I know....................you are all on pins and needles.

"No we're not!"

Don't blame you. My brain hurts. All for now. Enjoy!

[Tyson]

So how would this technology apply to audio equipment (I assume a DAC)?  For example I have an iFi iDSD Pro which has a plug for accepting an external clock.  Would something like this just plug into that, or would more extensive surgery be required?

[art]

Uhm.................this gizmo (both of them, actually) are USB-SPDIF converter thingies.

So, no.

As to what the gizmo you have, and what kind of external clock it would take................I have ZERO idea. Not my realm.

[art]

OK, looks like it is designed to take an external 10 MHz clock. You can buy a really good one, for around $30, on ebay. But, then you have to put it into a box, supply it with 12 V @ 1 A or so, and connect it to a BNC jack, so that you can connect it to the iFi gizmo.

[Tyson]

OK, thanks.

[art]

Actually..............now that I looked on ebay...................the days when 25 guys were selling them, for $30 are now the days of 5 guys selling them for $50.

[art]

OK, in yet another example of "why getting old sucks", it turns out I already did make a plot of what happens when you divide by 2 in the s/w, or the test fixture (h/w).



OK, should be pretty easy to understand. In the top plot, I run the 22 MHz signal into a D f-f, to get it to 11 MHz, because I know what a good clock looks like. In the bottom one, the 22 MHz goes right into the phase noise testing gizmo, and I tell it to divide by 2. From that, we can guesstimate how much a crappy little picogate adds.

The noise at 200 Hz is around 3 db higher. Yawn................

(Everything else is the same.)

OK, in all fairness, if the reference oscillator had a noise floor of -160 dBc (which good ones do), then you would see more detail. But this reference was chosen for its 1 Hz offset number (<-102 dBc), and not its noise floor. So, can't go below -150 dBc, but no one here is having a fit over that minor detail.

(BTW...............yes, it is one of those ebay specials that I have mentioned above. Darn good part, for that little amount of money.)

[art]

Here is a fair demonstration of what "random walk" can do to an expensive ($100 or so, if they would only sell you one) double-oven SC-cut crystal oscillators. IOW, about the best you can get. The reason I say "fair" is that for it to present a clearer picture it would have needed to be run over a longer time span, to average out the noise way down in the sub-sonic region. Also, looking at all of the data, it would have better better if we used a different supply. Probably, on the day these were taken, I used whatever supply I could grab that would work.

And, to be honest, I didn't think these would suffer the random walk problem. (Yeah, I should have known better.........................)

The top unit is one of those ebay specials I mentioned above. The next 2 are samples that someone managed to get, for 48 kHz clocks. (256x and 512x) I used the s/w to compare them to the 10 MHz reference, to make it easier to see how they stacked up.



As you can see, the break point is around 0.3 Hz, which is not far from where it should be. And you can see (not as clearly as I hoped) that there is a 10 dB difference, one decade lower than the break point. (Remember, the curve goes from 30 dB/dec to 40 dB/dec when the random walk kicks in.)

OK, so what is the point?

1.) Even really, really good, and really, really expensive parts can be affected by this. Luckily, it is easy to mitigate. Whether an individual clock is good enough to merit the effort is another story. To be honest, when I run across a sample that shows no promise, I shut the test down. So, I am sure even the crappiest parts will show the effect. Assuming its intrinsic noise is not so high that you will never see it. And even if you do see it and can fix it, the clock will sound so bad that you will never notice the difference.

2.) All clocks do not sound alike. This should surprise no one. There are lots of factors that go into that. If they all sounded the same, then why would one company put "HEAR THE DIFFERENCE!" in their spec sheet? Because you can hear the difference. (Whether or not those parts actually measure what they claim they do.................well, I better keep my mouth shut.)

(As an aside, yes, I have taken some of those apart. Don't ask why. I'll just say none of my "fixes" seem to help. But, as a result of the tests made on the 2 parts shown in this thread..................after that point we measured ALL test samples in a homemade environmental chamber. So, should not surprise anyone the "fixes" did not help those $30 parts, as we only tested them in a tightly controlled environment.)

3.) What goes on in the sub-sonic region DOES matter. This what I have a hard time convincing people. Folks want to believe in order to "hear the jitter" that you have to actually be able to "hear the jitter". IOW "what does jitter sound like and how will I know I am hearing it and if it is below 20 Hz then I can't hear it and you are nuts."

You don't hear the jitter! You hear its effects.

Which are 1.) nasty, bright, hard, brittle, rough sounding high end and 2.) loose, flabby, tubby, poor bass.

Or, to sum it up: "digititis". Get a good clock (and by good...............well, look at the clocks in the crap we make....................that gives you an idea what a "good clock" for audio is.

"And just how do YOU know this, and no one else does?"

Well, because we have more spare time on our hands, to not only measure stuff to death (and more importantly, the gear to do it), and because of our background, we knew how important it was.

let me digress a bit..................

Anyone remember some gizmo, that went on some old Philips-based CDPs called the Simply Physics IsoDrive? Anyone remember?

Remember what it did?

It tightened the bass.

It  cleaned up the highs.

No one knew how. Even the guy who did it. (He would never admit it, all he would admit was that he felt there had to be some sort of improvement in making the platter rotation more stable. And he was right. He made it more stable, in terms of rotational stability. IOW, he took out some of the "wow and flutter" in the platter. Which means he lowered any modulation caused by minute changes in the rotational stability.

Which meant....................yeah, you got it...............he lowered the jitter.

(At this point, someone will conjure up the image of the character "Miller" from "Repo Man". Except we are not talking about UFOs and time travel. it just seems like it!)

So, back to the subject......................yes, none of us can hear what goes on below 1 Hz, but that does not mean that we can not hear the effects of jitter, that low in frequency.

We know, for a fact, that you can. We have demonstrated in many times. (In fact, we went through a 6-month phase trying to figure out why things sounded one way one day, and something else the next. Yes, we blamed everything but.................our "friend", sub-sonic jitter.

Seriously, once you get that down (to a certain "magical" number), the soundstage becomes what audiophiles expect soundstage to be. But, you first have to get all of the other "jitter" down to a certain level before any of that comes into play.

Trust me. We put a lot of effort into it. Believe us or not. Your choice.

Our 'net connection is doing its daily "you really don't want to be online, do you" routine. This may have some typos, and I will check for that later. Posting before it get lost in the ether.

[brj]

Pat, first it's good to see you posting again!

Second, I haven't had time to digest everything here yet, but I've started and so just wanted to let you know that I appreciate the amount of effort that goes into just writing up a discussion like this, much less the work behind it.

Thank you!

(Now can you work this into a USB to I²S converter?    Yeah, I know... not intended for external connections, multiple conventions but no standard for connector type/pin-out, etc..)

[gab]

Art's website is:

https://ar-t.co/PRODUCTS.html

gab

[art]

(Now can you work this into a USB to I²S converter?    Yeah, I know... not intended for external connections, multiple conventions but no standard for connector type/pin-out, etc..)

There is another forum that I post on (that has NOTHING to do with audio, which is mainly why I post there) that has an odd practice called "blue font". I am one of its leading abusers!

Blue font is for sarcasm.................

So, imagine this in blue................

You could buy what we already make, and tap into the I2S output of the USB controller chip.

Send me a PM about this, ok?

[art]

OK, here is an interesting group of plots.

We make it our policy to not share data from tests that were performed, for profit, from one of our customers. If we shared everything we did, for free, then why would folks pay us? (A lot of folks don't understand why ANYONE pays us money, but, hey, if you need to know, and you don't have the gear, or experience to do it, what else are you going to do?)

In this case, I can make an exception.

1.) I honestly forget who we did this for, as it was not anyone we had worked with, and never worked with again. (They were probably depressed by the results. Can't blame them: they had us stop before we finished all 10 samples.)

2.) The outfit that made these parts is out of business, so I can present them as an illustration, and not as something you can run out and buy.



The first thing you might notice is that there is no #5. There is a reason for that. You can probably guess!

It was so bad......................if you have no way to measure this, how do you know if you get stuck with one of those. Since we do not make DACs, we do not measure what comes out of a DAC. Whether it would show up or not, well, can't honestly answer that one. Let's just say it will sound like crap, but these guys were a large enough company that they had no way of listening to every unit that came off the line.

But..............

Look at #7!!!!!!!!!!!!!!!!!!!

That one is so good, that it borders on the level of performance of an SC-cut crystal. Which can cost close to $100. And this is from a generic-looking HC-49 part.

Of the 6 units shown here, there is around 25 dB difference. 20 dB if you drop the really good one. With a spread that large, I would have a hard time advising a customer to use them. But, once you add in the dog, well, no way!

Don't know what the other 3 would look like, as they told me to shut it down, and to make sure I marked #7. You can bet they used that one for their lab standard, to compare other ones to, in listening tests. I can promise you that one will sound incredible.

One more thing about these.

If you only look at phase noise, at 100 Hz, because it is relatively fast and easy to do, you really can't sort out the not-so-good ones out as easily.



As an aside.............the worst unit measures below -100 dBc @ 10 Hz offset. Some outfit that I know makes a fairly expensive part that...............going by published data............theirs (and not mine)..............that isn't spec'ed that good.

I'll shut up at this point, and let y'all ponder that one. Mainly because I would like to stay on friendly terms with them.

[tubesguy2]

Great thread, Pat, which pretty much convinces me that the standard DIY approach of ordering a couple of clocks off of the worldwide web and replacing existing ones in a DAC or USB interface is a complete crapshoot.

On a positive note, it means I can just use the vacuum cleaner to pick up the ultra-tiny NDK clocks that have disappeared somewhere on the floor near my work area.