It has occured to me that I have not really done any sort of summary to these posts. As they have happened over a month or two not all my thoughts have made it into my posts. So I'll try for more of a summary....

First of all it is very important to realise that the amplitude of any noise arising from clock jitter is entirely dependent on the source material as the noise arises from modulation of the recorded signal. Thus it is definitely NOT a fixed level problem. If there is no signal there is no noise caused by jitter. This is crucial to understand as I have already presented calculations infering worst case noise at -56 dBFS on my own system. More accurately that maximum noise is -56 dB relative to a 20 kHz signal of whatever amplitude. Now I do not know of any musical instruments that produce fundamentals above 5 kHz (with the one exception of some instances of pipe organs) - although I stand to be corrected on this. This would reduce the figure of -56 dB to -68 dB relative to a 5 kHz sine wave. Now for a real instrument there may well be harmonics that slightly increase the rise time which is why I went for the absolute worst case scenario of 20 kHz which is highly unlikely to be produced by any instrument in a none transient manner!

The problem with this noise is that it is not at all harmonically related to the recorded signal (only the amplitude is) but is directly linked to the characteristics of the jitter noise itself. Just suppose we had jitter noise that comprised solely of 1 kHz sinusoidal phase noise (this is never going to happen - this is just an illustration). In the presence of my full scale 20kHz signal and with the jitter noise at 25ns p-p, then the jitter noise would be a 1 kHz sine wave at -56 dB. Clearly not very good but also a completely contrived example. In reality the jitter noise would be predominantly low frequency (with my MOTU) or essentially pink noise (as with my 01V). In neither case would this be particularly noticeable except that my ageing ears would not be able to hear the 20 kHz signal so I would only hear the noise! The good thing is that with "real" music being presumably audible to mere humans and therefore jitter noise would be a) lower in level and b) significantly masked by the "real" signal. In essence, the annoyance factor could possibly be equated to an amplifier with very poor intermod distortion creating a similar none musically related low level "mush".

Also it is important to understand that it will only be any slaved sound cards that are going to contribut any significant jitter noise, as the internal clocks of almost any sound card should have inherently low jitter. This may be interesting to those who use an external reference such as a big ben. I would only use this when using multiple soundcards and even then maybe not, depending on the jitter performance of the various soundcards when slaved.

It is also clear that most modern soundcards/converters are paying more attention to jitter noise so they will perform better than my set up but in fact they will not be so much better as to ignore jitter noise completely. These newer cards also generally seem to focus the jitter outside the audible band. They can only do this by focusing the noise as much as possible in the sub audible band. Thus it is more important than ever to make sure that you use high pass filters set appropriately to the recording. This is standard good practise but will also avoid any build up of low frequency mush arising from jitter noise as well as the other more usual sources.

I hope this puts a lid on this with a few practical tips on how to minimise any effects you may get from jitter noise.

As usual, please feel free to comment, criticise, question (or even acclaim!!! LOL) whatever these ramblings mean to you!

I wanted to say thanks, Mr Ease, for all the time you have spent explaining this tricky subject to a wider audience. It's contributions like yours that make RO stand out among the many audio forum websites.

My pleasure Boswell. I quickly realised that I had taken on quite a task... Having started though it was important to finish.

To that end I would appreciate your input if you think there are any issues I have not addressed or not explained properly. As always it is difficult to target this type of thing for the relative layman and I only hope that I have achieved some sort of understanding for such. I thought this was important given audiokid's original question and occasional other commentary (not necessarily on RO) that clearly does not fully understand the subject! I hate misinformation!

I just wish we could convince the marketing dept's to present jitter data in a meaningful way - I find cycle to cycle measurements are effectively useless in this respect.

Again, if anyone finds parts of my explanations incomprehensible, please comment and I will try to elaborate - or at least explain more clearly....

You are not only brilliant but so generous to have taken the time to put this all together. Wow. Thank you .

audiokid, you should never confuse experience with brilliance! :

I'm just happy the effort is appreciated.

djmukilteo, post: 350289 wrote: I've been following another forum thread where the ongoing discussion is external clocks. The discussion for the most part is high end clocks....
I guess I won't mention any names but the debate is 10Mhz atomic master clocks creating better perceived audio.

I was just reading back through my ramblings and realised I had never responded to this post. In my "other" life I have had quite a lot of experience with atomic frequency standards. Although atomic standards have extremely high long term stability (hence their use in GPS and many navigation applications), this does not infer any particular advantage when it comes to phase noise (which is directly related to jitter). Both Caesium and Rubidium standards work in the same way. A small phial of gas is externally excited by RF which is within a control loop which maintains a plasma within the gas. This plasma emits light which is detected to complete the loop - if the light goes out you might as well leave the room! This control loop contains an oven stabilised crystal oscillator which provides the usual 10 MHz output.

In essence what we have is a crystal oscillator locked to an external (but in this case atomic) frequency. Sound familiar? The problem with these loops is that they are dependent on an externally excited and detected phenomenon which depends on the plasma characteristic of the gas and also how well the electronics are designed. What I can say is that, with the measurements I made (many years ago) was that several different Rubidium standards had consistently better phase noise (and hence lower jitter) than that of any of the Caesium standards I measured. With the systems I was involved with back then this actually meant we used Caesium standards for one system (which required the best long term accuracy possible) and Rubidium for another as phase noise was more important than absolute accuracy (although the absolute accuracy of an ovened crystal was quite inadequate).

Whatever these results is really of little importance when we use one of these standards as an input to our soundcard's PLL as the outcome (in terms of jitter) will be more a function of the soundcard PLL. The only difference will be that your 24 hour track will play back consistently within a few picoseconds rather than a few nanoseconds! How this could possibly affect sound quality is quite beyond me as it is little more than microtuning gone mad!

My advice is spend the $6000.00 on something useful!

I honestly can't believe this! Over 1900 views and no questions....

Either (a) I have explained this far better than I thought (yea right!), (b) I have have been far too technical or (c) no one can be bothered. With so many views I can hardly believe it's the last option and it's certainly not the first so I'm thinking I've failed in trying to put this all into layman's terms.

Any other thoughts?

Hey... I think I can speak for the majority

You've cover it like a book and put a lot of time into this. We love you. Personally, my next task is to get this into our wiki so it doesn't get missed when ever clock jitter is mentioned.

We will be able to read over this for years to come. Whenever I am wondering about anything to do with this topic.... " sun shine!" RO / including all of the web will know where to look for your generous insight into the world of digital audio. Some may eventually get it all sorted to a point where we could ask in depth questions which I'm sure will come.

big audio hug from me, that's for sure!
 

I echo audiokid's thoughts:

You've covered this quite well - so well in fact, it's going to take some time for us laymen to digest it all.
FWIW, I've learned to be less concerned w/ jitter given your treatise and my (new) setup.

Your time and effort spent explaining this topic are much appreciated, even if under-appreciated.
I've followed along from beginning to end, and while some has been over my head, it's been a fantastic read, and well worth everyone's time, IMHO.

In the end, I too will refer back to this thread whenever clock jitter is a concern, or even a topic of discussion.

Thanks for the responses and appreciation. I didn't post to "feel the love" as appreciation has already been expressed but I was honestly surprised that with so many views there had been no questions. I guess I was right in that it got a bit too technical!

I hope that with a bit of time or study it should become clear but please let me know which bits went "over your head" and I'll try to explain again.

I have one for you.

Does poor power effect clock jitter in a mastering environment, or high end audio?

The devices power supply has to be designed properly to handle a range of power issues, under voltage, over voltage, transient suppression, surge suppression etc...
As for clock jitter, if your power supply can not maintain proper power rails to your clock circuitry then yes. But this is true for any circuit on those power rails. The power supply design is often under appreciated, but in high end audio a robust power supply is essential.... my two bits...

I would back what Link has said. I would also add that a recent bane of the lives of location sound recordists is the design and quality of the new wave of laptop power supplies. These horror devices are built to the absolute minimum requirements, and spray switching noise throughout the environment they are connected to, both through the laptop to the audio interface and also back out though the mains. In the majority of cases, the output voltage/current/connector is proprietary, and the manufacturers do not offer any way to spend a little more on a power unit to get a proper one.

It's one of the reasons that I use a rack of Alesis HD24XRs for location recording rather than a laptop with interface.

I know this appears to have little to do directly with clock jitter, but it illustrates the point that you are not going to get high-quality clocking where power units pollute the precision electrical circuits with un-related garbage.

It is much as Link and Boswell have said. I pointed out in post #14 that it was important that good power supplies were essential to good oscillator performance. "Dirty" mains supplies can have all sorts of noise on them and while a PSU in a soundcard could perform well for general noise it could also be awful at handling "spikes" on the mains. A good PSU should cater for all that the mains can send to your power outlet!

Basically anything that can disturb the normal operation of the oscillator or PLL is bad news and can certainly cause problems with clock jitter. However this only applies if the converters PSU is ill conceived. As Boswell stated much earlier in the thread, it is impossible to provide a general rule for jitter performance and the performance of individual units with respect to jitter would have to be seperately analysed.

I have for some time been meaning to give a link to this application note from the chip manufacturer Maxim Random Noise Contribution to Timing Jitter - Theory and Practice

https://www.maximin…

man, deep topic. I see this is a very important when we enter very high end audio. I also see the importance of very good power and conditioners that work. Most of this is over my head but I get it. Clean power is critical area in high end digital audio and mastering?

Good converters vs poor converters must deal with how they filter and are effected with the power.

Boswell, I haven't seen that particular app note before and it is certainly one of the better ones. Thanks for posting it here, very worthwhile. For the more mathematically adept readers it is nice for me that it covers almost exactly what I tried to in the non technical way - which I suppose is to be expected! The best bit to me though is that it does not talk of cycle to cycle jitter, probably because it is written from the RF perspective. Sorry folks if I'm like a dog with a bone on this! ;)

audiokid, yes of course, good clean power is always the best starting point and should be a must in a studio. Unfortunately you cannot always record "in house" (or maybe you can!) so it should always be incumbent on the designer (of whatever equipment) to try and deal with any mains borne noise within the box. This should be regarded as "de rigeur" on top end gear but, as usual, things like this adds an expense that becomes an easy saving on budget gear when they do little for the spec. sheets. While that may be a good general rule there will always be exceptions in either case. Caveat Emptor as usual...

You hear that expression used in top of the line Blu-ray players now. That they have improved clocks to eliminate clock jitter.

Clock jitter affects any product that uses either A-D or D-A converters so of course it affects Blu-ray just as it does DVD, CD etc. etc. While they may claim to have improved clocks, it certainly will not ELIMINATE clock jitter. Read through my posts and you will see why.

I see ads for very expensive power supply cleaners that ensure only clean regulated power goes to your equipment. Will this reduce jitter?

There is no fixed answer to this as it depends totally on your particular soundcard. As I have said already on this thread the biggest problems from clock jitter arise when you are using multiple synchronised soundcards or an external clock master. Every soundcard will have a minimum jitter performance that is defined by its design and is presumably what you will see in the spec. sheet. Noisy power can only add to this minimum and whether it will be a significant degradation depends on the ability of the power supply of the particular soundcard to reject that noise. This is very variable.

That said, clean power in a studio is always a good idea, not just from the point of view of clock jitter but also just about all the other sensitive gear around. Field recording is just the usual headache of what gear to take!

Thanks for the clarification.

Having read the explanation of Clock Jitter, I honestly can not say I have ever noticed it. At least not whilst watching Blu-rays. I don't recall hearing it in a studio, though I'm probably wrong there. As I am in no way an expert, unlike most of you guys and gals.

I would think there are very very few people that have heard what can be directly attributable to clock jitter. I also think that there is an element of "panic" in the audio world as another source of noise/distortion is recognised and accepted (although engineers in other disciplines have been battling with jitter for many decades!). There we go, now I'm expressing an opinion. That's almost bound to get a reaction so I'd better try and justify my opinion!

Unless a locked oscillator has some very specific audio frequency sidebands which would create audio noise at that specific frequency, then jitter noise should approximate to pink noise. Although the worst case figures I gave would (should) be quite noticeable, in practice the "real" levels of the jitter noise will be very much lower and therefore either amid the normal system noise floor or at least well below a strong signal.

The usual manifestation of truly random excessive jitter noise should be a signal dependent elevated noise floor. This is why very few will be able to positively determine that an elevated noise floor is caused by jitter as the noise floor will also reduce with the signal level. This also means that jitter noise will generally be unobtrusive - unless of course your clock has some really nasty sidebands.

In hindsight, I should perhaps have mentioned this much earlier. Thanks for prodding!

So it's not some the average Joe would spot?

Ryan Edward, post: 355194 wrote: So it's not some the average Joe would spot?

Well, in my opinion no! First, most people will be just using a single soundcard, at least in the domestic environment. As this does not involve locked oscillators and uses a simple crystal oscillator, it is unlikely to have a large jitter. This is just the nature of crystal oscillators and it would take some very poor design for such an oscillators to have jitter in the order of the 25 ns I measured with locked oscillators on my own system.

Secondly, the figures I gave using a 20 kHz sine give a maximum error which is - 56 dBc, where dBc is the measurement of the noise relative to the signal. For a 1 kHz sine, this reduces to -82 dBc. Compare these figures to say a vinyl disk. Due to the required RIAA compensation, this is just about the maximum theoretical S-N available for a disc input and that noise is constant and independent of programme material unlike jitter noise. I give these figures to try and put some meaning to the numbers and it is not within the capabilities of many systems (or ears) to truly reveal jitter noise.

In an industry where we can measure many many things, we constantly get theories about why A sounds different to B which usually involve some speculative mechanism which defeats the ability of objective science to measure (as IMHO the mechanism probably didn't exist in the first place). This really isn't one of them. We know about clock jitter and can measure it quite readily. Having measured it we can easily enumerate what the effects will be.

While it is good engineering practice to minimise any clock jitter and with the current apprehension about it, then any modern converters should really have battled the effects down to insignificance. I believe they have achieved this and it is not something that concerns me at least, even with my ageing equipment with (as Boswell said) HUGE 25 ns jitter. I have a pretty decent monitoring set up, and I certainly cannot claim I have ever heard anything I could ascribe to clock jitter. Most of my time mixing is concerned with much bigger problems than clock jitter! Personally, I never give it a second thought other than to try and answer audiokid's original question.

Thanks for the clarification.

I read reviews of very hi end Blu-ray player boasting of the fact of almost zero clock jitter and charging a premium for it. Sounds like these manufacturers are trying to make money on some thing that is negligible anyway.

Well, marketing departments are well aware of the debate and controversy surrounding clock jitter so I guess this is to be expected!

One company were promoting their ultra hi end Blu-ray player costing over $100K and all they were going on about was ultra hi quality clocks to prevent jitter. Seems like marketing BS to me. My $500 PS3 plays Blu-rays beautifully and I observe no jitter.

jasonthomas, post: 355597 wrote: One company were promoting their ultra hi end Blu-ray player costing over $100K and all they were going on about was ultra hi quality clocks to prevent jitter. Seems like marketing BS to me. My $500 PS3 plays Blu-rays beautifully and I observe no jitter.

Just to pick up on that, it is IMPOSSIBLE to prevent clock jitter. All electronic circuits have noise so the jitter can only be reduced - and I also indicated what levels of reduction might be achieved. I have already given figures on what reducing jitter will achieve in terms of audio performance.

Talking about different Blu Ray player claims is not the main thrust of what I have been trying to explain and I think I have already well covered this in responding to other previous comments just a few posts back. Now we're just going round in circles! Please bear in mind that there is a big difference when using a single clock and not slaving soundcards. Unless you slave an external D-A to a Blu Ray player then most of the problems with clock jitter are avoided anyway.

All this talk of jitter is making my head spin.

Well, after Jasonthomas paraphrased your earlier post, I did say we were going round in circles! Maybe you just got dizzy! :

My apologies. Didn't mean to derail the thread.

[[url=http://[/URL]="http://seminar2.tec…"]Here[/]="http://seminar2.tec…"]Here[/]'s a link to an on-line seminar entitled "Anatomy of Jitter", presented by Tektronix and due to go out on 11 Nov 2010. I suspect it may deal more with data transmission than with sampling of audio, but there is a lot of common ground.

@jasonthomas. No apology needed and sorry if I seemed a bit grouchy! This is not even my thread so it could easily be me that has derailed it!

Jitter in any digital music system is relevant especially if it is not well controlled and I was not trying to dismiss your point even though it had been covered a few posts earlier. In fact it gave me the chance to spout off a bit more... :<)

Boswell, post: 356213 wrote:  Here's a link to an on-line seminar entitled "Anatomy of Jitter", presented by Tektronix and due to go out on 11 Nov 2010. I suspect it may deal more with data transmission than with sampling of audio, but there is a lot of common ground. https://www.tek.com…

As you say, I'm sure this will be mainly aimed at data transmission (in view of Tek's recent scope releases!) but the brief synopsis does at least promise a bit more on general jitter examination.

Just a word of warning for others though, this presentation is going to be aimed squarely at engineers (of various abilities!) and not the lay person. As such it is highly likely to entail some slightly more advanced maths (mainly statistics). You may end up even more confused than before if you're not careful!

What I hope you should learn is that my presentations of peak clock jitter are somewhat simplified (but quite valid) from the mathematical analyses of the various aspects of clock jitter.

I took the time out to look at the Tektronix seminar (it is still available on the link and will normally stay around for a while).

Sadly, as Boswell and I suspected, it is solely focussed on data transmission. It does however give the "standard" analysis of the various factors contributing to jitter. This is of little interest to the general forum when I have already given some measurements of a typical audio system and also indicated where different causes of jitter could be problematic.

If you want to know more of the maths and statistics involved, by all means take a look but I don't expect you will find anything that really adds to what we have already discussed here.

MrEase, post: 356834 wrote: I took the time out to look at the Tektronix seminar (it is still available on the link and will normally stay around for a while).

Sadly, as Boswell and I suspected, it is solely focussed on data transmission. It does however give the "standard" analysis of the various factors contributing to jitter. This is of little interest to the general forum when I have already given some measurements of a typical audio system and also indicated where different causes of jitter could be problematic.

If you want to know more of the maths and statistics involved, by all means take a look but I don't expect you will find anything that really adds to what we have already discussed here.

"Solely focused on data transmission" is the topic here
I don't see any reason why the Tektronix white paper isn't completely relevant as that's what your talking about.
After all the only thing the clock is syncing is data transmissions...nothing else!

djmukilteo, post: 356865 wrote: "Solely focused on data transmission" is the topic here
I don't see any reason why the Tektronix white paper isn't completely relevant as that's what your talking about.
After all the only thing the clock is syncing is data transmissions...nothing else!

Well there are certainly different aspects to what I have discussed but I do not regard any aspect of this as (digital) data transmission rather than clock transmission. I may have discussed recovering a clock from S/PDIF or ADAT but I have not concerned myself with the associated data integrity, only the clock recovery and mainly the relative jitter between the recovered clock and the transmitted clock. In terms of data integrity of S/PDIF and ADAT transmissions then of course the seminar is relevant, however, with the data rates involved with these formats we have relatively huge margins for noise and in the eye diagrams and hence BER's are vanishingly low. This is why there is no real need for any error correction with these formats.

However the main thrust of what I have been trying to explain is the effects of clock jitter on the Analogue to Digital conversion, which has nothing at all to do with data transmission. Of course the elements of clock jitter are the same, as I have pointed out and discussed but there is no relevance to eye diagrams or BER.

MrEase, post: 356897 wrote: Well there are certainly different aspects to what I have discussed but I do not regard any aspect of this as (digital) data transmission rather than clock transmission. I may have discussed recovering a clock from S/PDIF or ADAT but I have not concerned myself with the associated data integrity, only the clock recovery and mainly the relative jitter between the recovered clock and the transmitted clock. In terms of data integrity of S/PDIF and ADAT transmissions then of course the seminar is relevant, however, with the data rates involved with these formats we have relatively huge margins for noise and in the eye diagrams and hence BER's are vanishingly low. This is why there is no real need for any error correction with these formats.

However the main thrust of what I have been trying to explain is the effects of clock jitter on the Analogue to Digital conversion, which has nothing at all to do with data transmission. Of course the elements of clock jitter are the same, as I have pointed out and discussed but there is no relevance to eye diagrams or BER.

Still just digital data being clocked into a digital converter chip nothing that special!