Educate me about Jitter

"Simple" is available. We, as audiophiles, oftentimes are our worst enemy and artificially create complexity where there doesn't need to be... hence the purpose of this thread to demystify what jitter is and whether it matters.

 

There is a huge difference between "entirely adequate" and "superior audio." You'll have to determine which target you are shooting for. Keeping this on topic, discussions of jitter pretty much must assume that 100% of the ones and zeros get to their destination unscathed. Once that happens (which is not hard at all, putting us at the 'adequate' level of performance), then we can focus on the timing elements (taking us to the superior level).

This is very true. But, many people don't like the only correct (or accurate, to coin a phrase) output. They prefer a little extra pizzazz or zing to be added.
Another thread is dealing with that right now at SH.TV. Which is fine. Nothing says we all must like, or judge, the same thing/way.

 

Good point. I think "does it matter" is certainly a personal appreciation aspect of audio enthusiasm. As buyers of audio goods, we must determine where we are on the audiophile spectrum. Someone hell bent on pursuing superior audio will fixate on every little detail, like jitter, to get the best audio they can. Others at the other end of the spectrum just want to hear satisfying sounds. It's all good.

 

This is true. I did some cutting and pasting earlier in this thread from an MIT paper that never mentioned audio once. But, I think that itself could possibly a component of the "we don't need to worry about jitter in digital audio" argument - the people most worried about jitter and solving problems relating to jitter aren't working in the audio sphere. Its easy for my to picture a DAC maker presenting a third party write up about jitter and its solutions on their website while omitting the fact the actual subject matter was medical device technology or something.

I think its telling you mention the 1980's - as I understand it audible jitter was a big deal then (in digital audio). It gets reduced further in every generation of DAC chip/receiver/etc. This is sort of my main point when it comes to jitter - when we're starting with something measured in quadrillionths of seconds, then steadily improve on it for 30-ish years, presumably if we haven't fixed the problem, we're getting really close, and we will soon. Eventually, (and I suspect we're already there), there will need to be a new boogeyman used by DAC makers to quantify differences. We can't blame issues with digital on jitter forever. But again, there is more to what makes a new DAC better then its predecessor then jitter. This isn't an all-DACs-sound-the-same conversation by any means!

 

If you want to see if you can hear the effects of jitter in your system, I think the old Stereophile test CD2 has jitter demonstration test tracks.

John K.

 

I'm curious as to how that works and what it demonstrates. It seems like if they went out of their way to put a high-jitter track on a CD, won't a DAC decode that as-is, intentionally preserving vs. filtering out the jitter? So the idea becomes "here is the sound of jitter you wouldn't hear on a modern system unless you're doing it on purpose?"

 

As far as I know the last time Jitter was an issue in the audio field was sometime toward the end of the previous century and the last time there was an attempt at seriously discussing the issue was in an AES article published by employees at Wolfson, which doesn't exactly make it unbiased, sometime around 2002-2003.

As recently as 2009 there were discussions about the impact of Jitter in several HT forums I used to frequent, but they were all obvious attempts to promote expensive S/PDIF coax cables. I think that the adoption of HDMI in HT market segment pretty much killed the incentive to use jitter since it was possible to use easier to understand words such as bandwidth.

In the absence of more recent publication and analysis I'll maintain my position that Jitter was the equivalent of the modern temporal blur buzzword.

 

I found this website with samples of how simulated audible jitter sounds like: what does jitter ACTUALLY sound like?

Hope this helps, OP!

 

An "entirely adequate" USB lead is one that transfers 100% of the ones and zeros, unadulterated. That is its sole function.

We are not in a position to consider jitter or timing until we can be assured that all the ones and zeros have reached the DAC, unadulterated.

I do not like the word "superior". It is used far too often when one is indicating one's personal preferences. It is a comparative term. We have no comparison here. It is of the essence that the DAC handles jitter, timing, and any other factors 100% effectively. That is the absolute basic. It shall recreate exactly the analogue that was converted to digital in the first place.

Then, and only then, a little colouration can be incorporated should you so desire. A little warmth, or some taming of the top end. But it is colouration and contrary to the true meaning of "high fidelity".

 

The ringing causes a lack of clarity. With effective isolation (I've successfully used Aurios and HRS Vortex footers under my DAC) the sound is clearer; much of the "hash" is removed, the background is "blacker," and imaging is improved. The effect is not subtle; it will be heard immediately by non-audiophiles (I tested it on my wife).

 

Interesting the television people went with the term, "judder" to describe the effect when transferring signal from one video standard into another.
(I hope this is not a threat hijack; just wanted to slip this in here...)
(Of course, if we also started discussing stutter, waffle or Jagger...well I can see how that would be...)

 

It's a good analogy since some people also don't notice judder and some do and each camp may not like the viewpoint of the other camp.

 

All I can say is that I'm glad I'm an aging rock musician with well-burnt ears, listening to mp3s in a car with road noise.

The things you guys can hear, that I cannot, must be torture sometimes.

 

Thanks for this link. Cool simulation.

As per the link, random jitter does very much look like a rise in the noise floor or "skirting" around a high amplitude signal whereas periodic jitter induces sidebands.

There's of course "simulation" and real life. As per the simulation in the link above where the author gives us 2us+ of jitter, reputable DACs these days have measurable jitter amounts in the tens to hundreds of picoseconds (1us = 1000ns = 1,000,000ps of course). The effect is so tiny that we basically need these Dunn J-Tests to stimulate and show the effects like the sidebands on a high precision FFT to demonstrate them.

IMO, with a modern asynchronous DAC like any reputable USB or ethernet device in 2018, the distortion introduced by jitter would be inaudible under any blind test conditions. Heck, a decent S/PDIF TosLink or coaxial these days should likewise be inaudible even though typically they measure worse. If truly someone claims they hear a difference between a decent DAC and one "upgraded" to a "femtoclock", it's not because they hear a difference from an improvement with lowered jitter. Human physiology is sensitive but simply not that sensitive!

BTW, that Stereophile jitter track on Test CD2 simulates a 2ns jitter. The effect is audible with a test signal like that but difficult in real music and as I mentioned above, modern DACs are operating much better than the Stereophile simulation!

 

Although I talked about decent DACs in 2018, in fact most of the devices I've looked at / listened to have excellent jitter measurements since the turn of the decade...

As others have suggested, as much as jitter has been used to differentiate devices from manufacturers as defining benefits, it hasn't been a "problem" in digital hi-fi for quite awhile!

 

The effects of jitter have been known for years. And IMO dealt with effectively to make it "not a problem" (for domestic audio users) ages ago.

Here's a paper from one of the engineers at the BBC R&D back in 1977 on the subject:-

Permissible timing jitter in broadcast PAL colour television signals - BBC R&D


NwAvGuy also covered the topic more recently here :-

NwAvGuy: Jitter Does it Matter?

 

A paper by Julian Dunn: http://www.audiophilleo.com/docs/Dunn-AP-tn23.pdf

 

This short video explains jitter and other digital issues in a very easily understood way.

 

It seems to me like you created this post with that answer in mind, and you were just waiting for the validation.

I'll be honest that I don't have good enough ears to hear jitter, but that doesn't mean that it doesn't exist or that it doesn't bother some listeners.

 

Entirely incorrect. I didn't even know what it was. How can I have a preconceived notion about something I'm not aware of?

 

Don't be too sure about it.

You take your analogue system seriously and hopefully you get excellent results from it.

Take a look at this clip. Their top of the range DAC is somewhat unconventional in appearance, but its vice (vise?) like grip on timing and what have you and its incredible ability at interpolation yield remarkable results. Even from mp3.

Speed and accuracy of processing seem to be quite important.

 

The Chord DAVE is, no doubt, a fine DAC, but I find a lot of the Chord video to be promotional BS. Chord is not the only manufacturer to use a FPGA instead of a conventional DAC. FPGA simply means that the designer can design his own chip, a one of a kind. As for ultimate sound, there have been DACs using conventional chips (like ESS) compared favorably to the Chord DAVE by main stream reviewers and particularly in the forums. The fact that the chip is, in relative terms, inexpensive (as proclaimed in the video) is irrelevant and doesn't mean it cannot perform as well when properly implemented. They can be inexpensive because they are produced in great quantity. Development research and cost for the chip, though, are far greater than the FPGA solution. That the Chord clock oscillator runs at 104 MHz is interesting (and ultimately that is the "vice grip on timing"). More BS. The clock on my DAC runs at only (?) 100 MHz, if you think that matters. But my DAC costs 15% of what the DAVE costs and I can tell you what the precise spec of my femto-second clock is, something omitted from the Chord video. Finally, the video speaks of a discrete analog stage, but the video shows the analog signal running through what look like ICs to me. What the real story is, I don't know but the video is no particular help and seems to serve up confusion--not unlike most conventional PR output.

In any event, the video does not reply to the question raised by the OP, that is what is jitter. If the OP wants to continue to believe jitter doesn't matter he is free to do so. There is a lot of audio equipment out there as well as ears that are totally insensitive to the benefits of great audio that so many of us strive for.

 

My non-technical understanding is that any audible degradation of digital sound quality due to jitter is no longer an issue in competently engineered audio gear.

But you have to admire the pure subjective connotative genius of the word itself in creating a nervous, twitchy FUD feeling that you ought to be worried about it and it's ruining your ability to hear the pure absolute sound.

Jitter!

 

Just for an example, and I may be showing my age but there were studies in the '80s, or at least demonstrations, around speaker wires and interconnect cables. Listening groups were able to discern differences between cables (and even between new and broken in cables) that could not be explained by any measurements including those normally used to measure cables. With the improvements in audio components and digital in particular, this seems more true than ever, and in particular has extended to digital cables.

But more to the point of this thread, the notion that improving jitter performance of an otherwise very good DAC cannot be heard is countered by experiments over at Head Fi (and Computer Audio, I think) where modifiers have substituted higher precision clocks (in one case that I know, one femtoclock for another) and credibly claimed clear improvement in what they heard. In fact, the American manufacturer Wyred4Sound recently offered a femtoclock upgrade (from a non-femtoclock) to its top-of-the-line DAC. Apparently its customers were quite happy with the results. Could one have measured the clear improvement in analog output in these cases? I really don't know but don't think so.

 

Jitter used to be a real problem in digital audio back in the 1980s and 1990s. The most characteristic term applied to its effects was the hard, glassy sound of CDs common on high-jitter hardware.

Like some have already mentioned, the jitter problem today has largely been licked in audiophile-level hardware and most modern players. You can still lower it at the margins but most hardware produced in the past 15 years produces jitter below the threshold of audibility.