An interesting paper on jitter audibility

[hciman77]

Originally Posted by odmanca

Don't mean to be rude but I find the above statement very odd coming from someone who is (or claim to be) an audio engineer.

Er, the man does hold something like 15 patents, 5 are audio related, for cables and connectors, so however strange his approach may seem to you (and me as it happens) I dont think it is fair to decry his engineering credentials.

A nice sig I saw at rec.audio.opinion is

Music is art
Engineering is science

Actually this is wrong anyway as engineering is strictly speaking the application of methods and techniques and knowledge which have been derived or discovered elsewhere (often by science)

Theodore Von Karman, an aerospace engineer, says, "Scientists discover the world that exists; engineers create the world that never was."

[audioengr]

Originally Posted by ezkcdude

hciman,

Thanks, for posting this. It is very enlightening. It shows two very important things: 1) Jitter is detectable, but only at much higher levels than you would guess from these forums and 2) The evidence from the second paper is even more striking because it does show that trained professionals, whose living is based on their ears to a large extent, do appear to be better at detecting jitter. This second point is interesting, because it is often claimed by jitter-busters, and now we can at least have some evidence for that. However, if one wants to cite this aspect of these Japanese researcher's work, then one must also acknowledge that, in absolute terms, jitter should not be audible in the amounts that exist in our stereo systems (unless it is artificially generated). I would suggest that whatever changes people hear when they measurably improve jitter in their systems are not due to the jitter itself, but rather to other changes in the signal chain. Chaos? I don't think so.

I dont agree that you con conclude either point (1) or point (2) above.

IMO, all it shows is that the tweaked-out audiophile systems are more resolving than the one in the first experiment, which is no surprise, given that I have yet to hear a stereo salon build a good-sounding system, in any city I have visited...

It also shows that the college students may have untrained ears, or minds for this type of listening. It takes experience to hear these things and not to go down the garden path...

It certainly does not prove that 100psec jitter cannot be heard by humans. It only demonstrates that using these particular systems with this group of listeners that the threshold of audible jitter was relatively high.

Steve N.

[audioengr]

Originally Posted by odmanca

Don't mean to be rude but I find the above statement very odd coming from someone who is (or claim to be) an audio engineer.

An audiophile can self-proclaim to have golden ears and defy all logic (I can hear the difference because I believe there is a difference, despite all measurements indicate otherwise.) But an engineer, being a man of science, should correlate his/her observations with the measurements before coming to a conclusion.

To say that measurements do not reflect what's audible is saying audio engineering is black magic; and black magic is not engineering because it's not based in science. Now it's possible the measurements (good or bad) do not correspond to what you hear, simply because the instrument is not made to measure the particular aspect of the audio spectrum of your interest, but that is not an excuse to ignore measurements in its entirety and its implications.

First, I have Audio Engineering schooling, but I am a EE with 30 years digital design and management experience. This is my moniker, nothing more.

Secondly, I am not proposing that measurements are not important. I have a lot of measurement tools that I use myself daily. However, I do not ascribe to the notion that just because it cannot be measured using classical techniques or is perceived to be at some low "threshold" of audibility, that it is not audible. They are still discovering things that humans can hear that they previously though were inaudible. The brain is a powerful tool, and this is what makes our hearing so good, not just stirrups and eardrums....

And furthermore, I like to thing "outside the box", believing that there are audible things that typical measurement techniques are not showing. Being in the cable business for 10 years has taught me that much. I'm not saying that the phenomena cannot be measured, only that typical techniques are not showing them or that the perceived "thresholds" of these measurements are artificially high.

Steve N.
Empirical Audio

[audioengr]

Originally Posted by hciman77

I think suggests is a better word than shows, remember that in the 2nd expt subjects had their own systems and choice of material. Thus there are three fundamental ways that the 2nd expt differs from the first

1) Listener type (students vs pros)
2) System familiarity (standard system vs own system)
3) Material familiarity (forced material vs chosen material)

Any 1 variable or combination of variables could contribute towards the better performance, of course one could easily isolate these variables and test them separately. Are pros better ?, maybe, it would be nice to think so in the sense that I would prefer CDs mastered by folks who can hear the difference between good and mediocre.

Your 3rd point is an excellent one, as are the others. I have found myself, that in order to highlight and make audible certain phenomena such as jitter, it is critical to choose the optimum program material, ala music tracks. I can play any number of tracks to an audience that will not expose the effects of jitter, even really large amplitude jitter. But the object is to expose the jitter, so careful selection of tracks that do this is warranted. Playing tones is equally useless in this regard IMO. I have found that it needs to be music with HF transients and good imaging depth and width, and not too busy.

Steve N.
Empirical Audio

[ezkcdude]

So, here's a question for you, Steve. When you do the single-blind listening test, what is the setup? In this paper, at least, they adjusted the jitter by using software, so that everything else in the signal chain is constant (between listeners obviously). When you ask someone to listen to two systems, A and B, with differing levels of jitter, what are the variables that change besides jitter? Without using software, which would probably be difficult to program less than 100 ps of jitter, how do you know you are testing the audibility of jitter, versus some other change in the signal chain. For example, it would clearly be nonsense to switch between two different DAC's, let's say Benchmark and Bel Canto, and claim differences between the two are due to differences in jitter alone. I'm sure these two have different jitter measurements, but there is so much more involved than that. Can you give us an example, just one real world example, of how you tested the audibility of jitter using a controlled experiment?

[Kees]

Originally Posted by audioengr

First, I have Audio Engineering schooling, but I am a EE with 30 years digital design and management experience. This is my moniker, nothing more.

Secondly, I am not proposing that measurements are not important. I have a lot of measurement tools that I use myself daily. However, I do not ascribe to the notion that just because it cannot be measured using classical techniques or is perceived to be at some low "threshold" of audibility, that it is not audible. They are still discovering things that humans can hear that they previously though were inaudible. The brain is a powerful tool, and this is what makes our hearing so good, not just stirrups and eardrums....

And furthermore, I like to thing "outside the box", believing that there are audible things that typical measurement techniques are not showing. Being in the cable business for 10 years has taught me that much. I'm not saying that the phenomena cannot be measured, only that typical techniques are not showing them or that the perceived "thresholds" of these measurements are artificially high.

Steve N.
Empirical Audio

I wholeheartedly agree with this.
I would like to add:
The formulas, "laws" , methods and measurements the engineer uses are a "working model" of the reality he tries to deal with. It gives a view on what he thinks is reality and some means to predict what will happen in reality in certain circumstances and under certain conditions.
It is a tool. A map of part of reality as we know it.
It is not reality. It is just a model of it.
The map is not the territory.
In the territory are numerous things that are not on the map.
In reality are numerous things that are not in the working models of science.

[hciman77]

Originally Posted by audioengr

IMO, all it shows is that the tweaked-out audiophile systems are more resolving than the one in the first experiment

but.....

Originally Posted by audioengr

Every system is at some level of perfection, there is just no way of telling where these were, at the bottom or the top. More likely in the middle IMO.

and....

Originally Posted by audioengr

1) systems provided by listener, which included sometimes speakers and headphones. The quality, imaging and resolution of these systems is in question.

Er, will you then concede point 1 above ?

Originally Posted by audioengr

It also shows that the college students may have untrained ears, or minds for this type of listening.

Or may not, without a different set of subjects for comparison in the same setting it is speculation.

It takes experience to hear these things and not to go down the garden path...

How much training does it take to improve discriminative ability by a factor of say 2500,
from 250ns to 100ps

It certainly does not prove that 100psec jitter cannot be heard by humans.

Since not all humans have been tested clearly not, nor have I ever said that in this thread, but can you prove the positive case ?

It only demonstrates that using these particular systems with this group of listeners that the threshold of audible jitter was relatively high.

Steve N.

Well, the sample consisted of a range of listeners and a range of systems. If you have a big enough range you begin to approach generalizability.

This is a data point but interesting as the figures are so high on this and on the prior study.

We interpret the importance of this differently, fine, life would be dull if we all thought the same.

[audioengr]

Originally Posted by ezkcdude

So, here's a question for you, Steve. When you do the single-blind listening test, what is the setup? In this paper, at least, they adjusted the jitter by using software, so that everything else in the signal chain is constant (between listeners obviously). When you ask someone to listen to two systems, A and B, with differing levels of jitter, what are the variables that change besides jitter? Without using software, which would probably be difficult to program less than 100 ps of jitter, how do you know you are testing the audibility of jitter, versus some other change in the signal chain. For example, it would clearly be nonsense to switch between two different DAC's, let's say Benchmark and Bel Canto, and claim differences between the two are due to differences in jitter alone. I'm sure these two have different jitter measurements, but there is so much more involved than that. Can you give us an example, just one real world example, of how you tested the audibility of jitter using a controlled experiment?

The jitter demonstrations that I have done compared the following in chronological steps:

1) Stock CD Transport playing a commercial CD track into modded P-3A DAC using S/PDIF
2) Stock CD Transport playing low-jitter copy of same track into modded P-3A DAC using S/PDIF
3) Modded CD Transport (same model) playing low-jitter copy of same track into modded P-3A DAC using S/PDIF
4) Computer playing same ripped track using Off-Ramp USB converter and S/PDIF to modded P-3A DAC
5) Computer playing same ripped track using Off-Ramp USB converter and I2S to modded P-3A DAC

DAC was the same one used for all experiments, same preamp, same amps, same speakers. The jitter was reduced (more precise and clear imaging) in each step. The listeners are all in front of the equipment, so they cannot see what I am doing. The playback equipment is changed back and forth using A/B teminology, changing which ones is A and B at random etc.. Much like what you get when you are being fitted for glasses.

The vast majority of listeners were able to hear an improvement in each of the 5 steps. A few had limited HF hearing, so they didn't. The only difference was the jitter in the digital signal(s). Measurements were not taken, but I had previously looked for the difference in jitter between the S/PDIF and the I2S from the Off-Ramps and I cannot see it on my 2nsec resolution scope. If it was a 500psec difference, I would have seen it.

You must understand that my CES setups are some of the most resolving that you will find at CES. It is essentially my same reference system that I use for the business. I have complete control over all components, speakers and cables. I dont share with any other vendors. Everything in the system is built by me or modded by me.

Steve N.

[ezkcdude]

Well, I think we're getting closer to something meaningful. So, let me ask. What do you mean by "low-jitter copy"? I assume you have ripped a CD track, and then burned it again using some "low-jitter" technique. How is this done?

More importantly, without your actually measuring the change in jitter, let alone whether it is increased or decreased, why should one take it at face value that the copy is lower jitter? If you could show us some data (jitter spectrum, for example) for your copied CD's versus the original, then your test would have much more weight.

Also, when your "testers" at CES are doing the listening, do they know which source they are listening to? If so, one can easily make the arguments for a) placebo or worse b) they are just being polite.

[hciman77]

Originally Posted by audioengr

The jitter demonstrations that I have done compared the following in chronological steps:

1) Stock CD Transport playing a commercial CD track into modded P-3A DAC using S/PDIF
2) Stock CD Transport playing low-jitter copy of same track into modded P-3A DAC using S/PDIF
3) Modded CD Transport (same model) playing low-jitter copy of same track into modded P-3A DAC using S/PDIF
4) Computer playing same ripped track using Off-Ramp USB converter and S/PDIF to modded P-3A DAC
5) Computer playing same ripped track using Off-Ramp USB converter and I2S to modded P-3A DAC

DAC was the same one used for all experiments, same preamp, same amps, same speakers. The jitter was reduced (more precise and clear imaging) in each step. The listeners are all in front of the equipment, so they cannot see what I am doing. The playback equipment is changed back and forth using A/B teminology, changing which ones is A and B at random etc.. Much like what you get when you are being fitted for glasses.

The vast majority of listeners were able to hear an improvement in each of the 5 steps. A few had limited HF hearing, so they didn't. The only difference was the jitter in the digital signal(s). Measurements were not taken, but I had previously looked for the difference in jitter between the S/PDIF and the I2S from the Off-Ramps and I cannot see it on my 2nsec resolution scope. If it was a 500psec difference, I would have seen it.

You must understand that my CES setups are some of the most resolving that you will find at CES. It is essentially my same reference system that I use for the business. I have complete control over all components, speakers and cables. I dont share with any other vendors. Everything in the system is built by me or modded by me.

Steve N.

1) Jitter on CDs - does that make sense ? i.e the bits are read correctly or not and buffered into the word clock and then clocked out. Any timing variations on read would surely be irrelevant unless bits were wrong or somehow the buffer was not filled, can that happen ?. I thought jitter was only a problem at D/A and A/D stages ?

2) I think the 3;4 step may be flawed. Computer transports are much better at error correction than CD transports as they cannot tolerate a single bit error, thus going from 3:4 must improve bit error rate i.e a variable enters here.

3) A modded transport may have other changes such as different SNR, THD, FR, Dynamic range, RFI noise and so on, can you verify that all these were unchanged in the mods

4) Did you check the bit error rates on the S/PDIF and I2S cables ?

Not saying the changes didnt improve things but not sure you have proven that you have isolated jitter as the culprit

5) Did you verify that some listeners actually had worse HF sensitivity and that only those listeners failed or was this your interpretation for those who failed ?

5a) What was the highest frequency on the track ?

6) Did any listeners with HF deficiencies get it right ?

7) Define vast majority and few

8) Did you check that the audio levels were the same for each condition ?

9) What exactly did you say to listeners, this is important as it is very very easy to accidentally skew results by varying instructions ever so slightly or accidentally exposing your expectations i.e "NOW listen to this"

Thanks for the clarifications.

[drarthurwells]

And BTW, what does it mean when you say I "Jeff Goldblum you"?

Is that something you can tell me in public?

Originally Posted by ezkcdude

Have you ever seen Jurassic Park? If not, rent it.

Isn't that a children's movie? Seems I did hear of it.

[drarthurwells]

Originally Posted by Toe :
TO: drarthurwells. Just a heads up, in that long reply to ezkcdude you seem to have completely forgotten to provide any actual evidence, or even a coherent hypothesis, of how chaos theory applies to jitter being something that's audible, or to cite a source that does.

Originally Posted by morphsci

Well he doesn't really have to. One of the tenets of chaos theory is that in chains of correlated events a small change early on in the chain can have much larger consequences farther down the chain. This is related to the problem of statistical error propagation. The question then becomes, is a chain of audio components long enough for significant error propagation effects to be detected? Discuss ...

Good to see someone else understands Chaos theory.

One other factor is amplification of error effects in a source. A very small error (in reading a CD) goes through many steps of processing and amplification before it even reaches a speaker or headphone. A small reading error can then emerge as much larger an error before reaching a speaker or headphone. Related to large scale chaos eventually emerging from an insignificant small beginning.

[drarthurwells]

Originally Posted by hciman77

1) Jitter on CDs - does that make sense ?

Doesn't make any sense if: the analog recording is free of timing/phase errors, and the analog to digital conversion is free of timing/phase errors, and the embedding of data on a CD is free of any timing/phase errors, and if Santa Claus brings me the 72 virgins I asked for.

[audioengr]

Originally Posted by ezkcdude

Well, I think we're getting closer to something meaningful. So, let me ask. What do you mean by "low-jitter copy"? I assume you have ripped a CD track, and then burned it again using some "low-jitter" technique. How is this done?

Yes. I use a battery-powered Superclock clocked CD writer. It is definitely lower jitter than the original, as is the Reality check. Reality Check did shoot-outs with me at CES last year. They were both excellent superior copies

Steve N.

[audioengr]

Originally Posted by ezkcdude

More importantly, without your actually measuring the change in jitter, let alone whether it is increased or decreased, why should one take it at face value that the copy is lower jitter? If you could show us some data (jitter spectrum, for example) for your copied CD's versus the original, then your test would have much more weight.

Also, when your "testers" at CES are doing the listening, do they know which source they are listening to? If so, one can easily make the arguments for a) placebo or worse b) they are just being polite.

The CD copies were verified to be bit-identical to the original, so the only variable changing is the jitter.

The Testers did not know until after they voted what they were listening to.

Steve N.