[nick_charles]

Quote:

Originally Posted by Pedja /img/forum/go_quote.gif .....you can observe this...by spectral analysis), or you can measure the audio output signal observing frequency modulation of high frequency audio carrier. Pedja

From what I have seen even jitter at huge levels (-20db) has a minimal effect on the frequency spectrum below 20khz, once you go above 20K it can be massive but you are dealing with energy levels are normally extremely low anyway and so the effect though it looks impressive may be of limited audibility even here. When you lower jitter to levels found in the very worst of commercial kit the effect on the waveforms is utterly microscopic and within the scope of random variation.

 

[nick_charles]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Pars, how would you measure jitter of a transport/DAC, is there a test method with NIST traceable standards? Is there an ASTM for jitter in a transport/DAC combo? Any measurement is only as good as the test method. What is the 90% CI of these jitter measurements, are they repeatable? Has there ever been a Guage R&R?

Stereophile do some jitter testing which does include testing transport/DAC combinations, the precise technology I am unsure of but I bet if you asked John Atkinson(editor) he would give you a straight answer about what they do and what kit they use for it ?

 

[regal]

Quote:

Originally Posted by nick_charles /img/forum/go_quote.gif Stereophile do some jitter testing which does include testing transport/DAC combinations, the precise technology I am unsure of but I bet if you asked John Atkinson(editor) he would give you a straight answer about what they do and what kit they use for it ?

Do you honestly trust Stereophile magazine to give a certified trillionth of a second measurement?

Its akin to asking my local newspaper to take an exothermic measurement of splitting an atom.


There a many accepted jitter measurement techniques, but none for a transport through a DAC.

 

[Pars]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Pars, how would you measure jitter of a transport/DAC, is there a test method with NIST traceable standards? Is there an ASTM for jitter in a transport/DAC combo? Any measurement is only as good as the test method. What is the 90% CI of these jitter measurements, are they repeatable? Has there ever been a Guage R&R?

Got me, but I would guess in the same way as a one-box CDP. All you are concerned about is the jitter that appears on the BCLK of the DAC chip.

 

[regal]

Stereophile's best interest is pushing $10k transport suppliers. The internet is a good check and balance.

 

[nick_charles]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Do you honestly trust Stereophile magazine to give a certified trillionth of a second measurement? Its akin to asking my local newspaper to take an exothermic measurement of splitting an atom. There a many accepted jitter measurement techniques, but none for a transport through a DAC.

I have no idea how accurate Stereophile's measurements are, I know that they use a Miller Audio Research Jitter Analyzer, whatever that is ?

 

[regal]

Quote:

Originally Posted by nick_charles /img/forum/go_quote.gif I have no idea how accurate Stereophile's measurements are, I know that they use a Miller Audio Research Jitter Analyzer, whatever that is ?

Paul Miller is also surprise, surprise an employee of Stereophile magazine. Smoke and Mirrors.

All we care is how a product sounds, they can keep their pseudoscience.

 

[tfarney]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Stereophile's best interest is pushing $10k transport suppliers. The internet is a good check and balance.

Not that I believe the editors of Stereophile are immune from the audiophile kool aid (on the contrary...), but I would think their best interest is in pushing the much less esoteric products that can actually afford ads in their magazine and on their web site.

Then again, they may just suffer from journalistic integrity.

Tim

 

[Pars]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Paul Miller is also surprise, surprise an employee of Stereophile magazine. Smoke and Mirrors. All we care is how a product sounds, they can keep their pseudoscience.

In looking up the Miller system (google) I came across a rather interesting thread on diyaudio. JohnW is John Westlake (ex. Cambridge Audio, has his own company now).

And as for Stereophile, I would trust their measurements before their assessment of sound in alot of instances

 

[bigshot]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Do you honestly trust Stereophile magazine to give a certified trillionth of a second measurement?

If it's so small, the engineers at a technology magazine can't measure it, how the heck are we ever going to hear it? This sounds like the same sort of argument used to justify the unmeasurable mysteries of high end cables.

Inevitably, when presented with facts and figures that show that a problem is inaudible, instead of determining that it doesn't matter, some folks go off on a tangent extending the zeros behind the decimal point a couple more times. The whole thing gets mixed up in arguments over testing procedure and the simple truth gets lost in the shuffle.

Jitter at the levels it occurs in home stereo equipment is below the threshold of audibility for even "golden ears" audiophiles and professional sound engineers.

See ya
Steve

 

[Pedja]

This kinda goes in circles...... I didn't hear any of you answered that (s)he does belongs that fraction.

Quote:

Originally Posted by Pedja /img/forum/go_quote.gif Anyhow, one has to induce jitter and to remove it in a controlled way to get some idea about its audibility. Unfortunately, only a fraction of people has such an experience.

As for the Stereophile measurements method.... The first important thing to understand is that there is no "Stereophile measurements method". Stereophile has been initially taking jitter measurements using Remy Fourre's (UltraAnalog) method of clock demodulation. Once the content of modulation has been split from the clock signal, it was shown in the frequency domain. This is quite good method but it requires opening the device under test and detecting the right clock line (the one actually used for DAC triggering).

Later they moved to Julian Dunn's (Prism, Audio Precision, Nanophon) method which measures the jitter analyzing the audio output. Since there is an exact relation between the jitter and its resulting artifacts, by using appropriate measurement signals and measuring particular artifacts, one can retrieve the jitter figure that causes them. There is an exact math and firm theory behind, and even better, all this is freely available online for everyone who wants to actually read. Paul Miller uses this method.

A J-signal is the one normally associated to this method. One however doesn't need to use this signal, high frequency sinewave is adequate, though it won't show the effects of data related jitter. J-signal is designed to provoke data related jitter (the one that appears when data hits the line) and to include it into the figure. It is ideal for measurements of interfaces susceptible to the data related jitter, and S/PDIF is exactly such an interface. That's why some people think that this signal is adequate only for systems using S/PDIF (so for separate transport/DAC combos) while it is inadequate for, say, integrated players, but this is not correct: there is nothing that makes its use inappropriate anywhere. As a shortcoming, one can spot its inherent threshold of about 130ps for 16 bit format, but this applies to the overall figure only. When you do the spectral analysis, you normally see below this threshold.

All this is only used by Stereophile, as well as by Hi-Fi Choice and Hi-Fi News and by a few other magazines, and you don’t have to blame them for this. You can rather blame the others for not doing such measurements (or any other jitter measurements for that matter).

Pedja