Why the preoccupation with jitter?

[Terry Demol]

Re: New clocking method

Prompted by KBK's post re. a new clocking method, I've been letting my imagination wander ....

How about using a sample and hold type circuit after I/V conversion from an R2R dac, and clocking that from the Word Clock? Any jitter in the filter and DAC chip would be nullified. The Word Clock itself could of course be derived from a stable master oscillator.

What do you think? This idea has just popped into my head, so please be kind in case I have missed something obvious.

Good idea but has been done before.
1 - Ultra Analog DAC module as used by Sonic Frontiers.
2 - dB Technologies (now Lavry Engineering)
http://www.lavryengineering.com/
goto products / DA-924. I recommend downloading the user
manual. This DAC was designed years ago and was an absolute
masterpiece of innovative thinking back when 24/96 chips
were only just available. It uses discrete high voltage R2R with
S+H OP.

Cheers,

Terry

 

[Guido Tent]

Surely there is more to Digital Audio than Jitter.

It's just that at this point the DAC chips are made good enough, that you can barely hear difference. But there is great difference in the sound of different apparatus using the same DAC's. Why? Well assuming the data stream is the same, the only difference left can be the analog stage (which is very critical if you want to have a good sound performance) and ... yes: Jitter.

All the best from Lars Clausen

and the power supply, and the parts quality, and the layout, and the DAC silicon layout (crosstalk of data related jitter to internal clock) and the PCB and cabinet material, just to mention a few others.....

merry christmas to you all !

 

[Guido Tent]

There is another aspect on the jitter problem that I have
been wondering about and that I cannot remember ever
seing discussed. While audiophiles have for quite some years
put a lot of effort into jitter reduction in their CDPs and there
are a lot of replacement clocks available, what is the situation
at the studio end, ie. in the AD part of the chain? Are the
AD converters used for recording designed for low jitter,
or is this a still neglected thing there, or has it perhaps been
known and taken care of since long ago? Anybody who knows? [/B]

Hi

The AD converters that I designed and built have all a very low jitter clock (guess which one), extended and super low noise supplies (all seperated) and a novel clock distribution scheme / buffering.

Once the A to D conversion has taken place, distortion due to jitter can never be eliminated anymore, contrary to the convesrion from D to A.

I do not know clock quality of other DACs

regards

 

[Pjotr]

Look around at this site:

http://www.dcsltd.co.uk/ProProducts.htm

Also some interesting tech info around there.

Merry Xmas to you all

 

[fmak]

I do not know clock quality of other DACs

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It is difficult to tell. Most XO manufactureres don't give jitter figures. Those who do don't do it for TTL XOs. Seems that ECL and PECL outputs are associated with super low jitter. Though they don't explain whatv ECL and PECL are .

Would someone care to enlighten me. If the outputs fully suit the dac processors, themn it should be easy to get super low jitter XOs.

 

[KBK]

jitter as an issue

I think the big issue is not really jitter reduction on it's own as an issue, but jitter in terms of overall bandwith of the jitter spectrum as a complex calculation and issue. Ie, jitter levels over a wide bandwidth. If this figure can be dropped over that huge bandwidth, then you've got something to crow about.

 

[fmak]

Re: jitter as an issue

I think the big issue is not really jitter reduction on it's own as an issue, but jitter in terms of overall bandwith of the jitter spectrum as a complex calculation and issue.
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I think it is even more complex, involving jitter in the whole chain.
Posters in this forum talk a lot about clocks and their jitter. However, even very low jitter systems benefit from having an external word clock. The improvement there is beyond what can be achieved fine tuning individual components and using plls etc.

I have a dCS system whereby I can use the source clock, an internal clock in the processor, and external word clcok. Even with a relatively cheap word clock, I have achieved an amazing degree of resolution improvement! It seems that different very high quality clocks impose there own sonic signatures and well as the cables distributing them!

It is essential that we eventually find a cheaper method of measuring very low jitter (O(1pS)) in a system.

 

[Lars Clausen]

fmak and KBK: I agree completely with your views. We performed some listening tests on two almost identical clocks, with just the difference that one had added 20 pS of random jitter in the 10 - 100.000 Hz span.
The test were performed on a set of 20.000 $ Dynaudio speakers that are known to be revealing on the qualities that a ref. clock can contribute. Soundstage, perspective, instrument placement, resolution, and a firm bass.

The result of this test was that there was no noticable difference between the sound with the two clocks.
Reverting to the original CD clock (on this Audio Research CD2) proved a huge difference for the worse. So it's not just about the amount of jitter.
At least not if you are at a fairly low level. Some CD players have so much signal related jitter from the built in clock, that you can actually hear the sounds and music from the CD if you connect a monitor speaker to the recovered Jitter signal. Levels of 200 - 500 pS is normal.

 

[fmak]

The result of this test was that there was no noticable difference between the sound with the two clocks.
Reverting to the original CD clock (on this Audio Research CD2) proved a huge difference for the worse. So it's not just about the amount of jitter.
--------------------------------------------------------------------------------

Two interesting aspects. First, some crystal manufacturers state that crytsla have lower jitter than XOs. So, provided that pghse noise is dealt with, why is everyone making XOs? Second, to what extent does the shape of the clock signal affect sound quality? I have a Sony digital tuner (777ES) with the 'sonic signature of digital radio', a very good spdif wave shape; a good clock, but with quite a bit of low amplitude hf on the top hat. When this clock is substituted by a 48kHz word clock, the sound cleaned up and the digital hash os gone!

 

[Lars Clausen]

fmak: Are you listening to the tuner's DAC or an external dac through SP/DIF in this test?

 

[fmak]

fmak: Are you listening to the tuner's DAC or an external dac through SP/DIF in this test?

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External dac . Any comments?

 

[Lars Clausen]

In this case i would say the improvement comes when your internal dac clock is derived from a house clock rather than the signal dependent SP/DIF packed clock.

The house clock is clean of audio signals, and should therefore contain no harmonics of the audio signal, thus the improvement in perspective + other.

 

[KBK]

Pardon my ignorance of clocking circuit design parameters and usage.. I know I know what is wrong with things and how to fix them, and don't specialize in the area of circuit design.

The question: If a clock is derived from the signal, ie, a CD input into a (my current DAC situation) Behringer DCX2496 digital Crossover, if the CD clock is very low jitter, does this translate to better performance from the Behringer? Or, can I go into the Behringer, fix it's clock and not worry too much about the Digital (SACD, CD, DVD-A) coaxial signal/clock (from what you appear to be saying, the clock is arriving with the digital data into the Behringer) data source?

 

[jackinnj]

another good article on Jitter

I am just tacking this on to the thread, in order to refrain from starting a new one -- Texas Instruments "ANALOG APPLICATIONS JOURNAL" , just out, has a good mathematical discussion :
www.ti.com/aaj

 

[sam9]

Thanks for the TI article. I only looked at it briefly for now. The paper dealt mostly in the Mhz range. Looking at fig 3 and whipping out a ruler to exprapolate back to the audio band, unless the jitter experienced in audio systemsis much, MUCH greater than inthe tables displayed, it won't be keeping me up at nighty!

How much alleged jitter are we talking about ibut also or reflections in the interconnent that the cable fetishists keep taliking about.

 

[Jocko Homo]

Around 500-1000 nSec, on a typical SPDIF setup. Good CD player.........10 nSec or so. There is a big difference, and yes, you can hear it.

Jocko

 

[gmarsh]

Around 500-1000 nSec, on a typical SPDIF setup. Good CD player.........10 nSec or so. There is a big difference, and yes, you can hear it.

Jocko

Doesn't SPDIF, at 44.1KHz, have a bit period of 350ns?

From this, I conclude that typical SPDIF setups don't even function at all.

 

[Jocko Homo]

Oy.......they need to invent syntax check too.

Yes......I was working on something in the nSec range, and it was on what is left of my brain.

Change nSec to pSec.

OK........you got me on that one..............my mistake for the year.

Jocko

 

[sam9]

Changing "n" to "p" in JH's post and apply a ruler and eyeball, the range of results goes from plausibly (but not intensely) audible to no way. Even if my ruler isn't straight I think that's fair conclusion.

All kind of moot since a survey of product spec sheets failed to show a jitter stated. A lcertain amount of "we've done wonderful and expensive things to reduce jitter" marketing puffery, but little hang one's hat on.

 

[Jocko Homo]

I am not in the business of selling stuff to fix those problems, but I can assure you that the ones that work are not trickery. (OK, some may be bogus, but only because they were done wrong.) The audible differences may sound subtle, but are a lot more plausible than all the other nonsense about cables and other audiophile nervosa products. Until you have actually heard the difference, you are not in a position to claim that jitter talk is all nonsense.

Absolute jitter numbers, if published, would be of dubious value if not accompanied by the jitter spectrum.

Jocko