What does Jitter sound like?

"Dgarretson - Wow and flutter exhibit the same results as jitter, frequency modulation, so the answer is yes, although some jitter occurs at rates and changes in ways that a turntable could not physically do."

Interesting to find this. This is what I hear and people say I'm crazy so this helps me feel more normal.

The sound of one bit clapping. Hardly an issue in modern design cd playback systems. The TI/BurrBrown chips, transports and all are from essentially the same sources. I am not denying there are design and thus sound differences-- some more pleasing to some of the people some of the time.....

Also I will admit there are other factors in the digi stream as well. Have intentionally kept my ears away from mega-buck digi-playbak systems for fear of endless dissatisfaction and upgrades for minor and subjective improvement.

It will prove that the jitter with your CD player and a commercial CD IS audible if you hear ANY difference.

Excellent - if it is indeed proven then you might consider an AES paper to corect these misleading studies - that is probably how to best spread the word..

Shadorne - this paper is more meaningless than my jitter samples. The system and music tracks used for this test was a joke. No conclusions can be drawn from this study IMO.

At least with my jitter sample (requested by many on Head-Fi), you can hear the difference between a standard CD and a re-written CD. It will prove that the jitter with your CD player and a commercial CD IS audible if you hear ANY difference.

Steve N.

Rotarius,

Having samples with jitter to compare would be meaningless unless the amount of jitter is quantified.

I agree. If you are interested there is an AES Paper published where they studied the audible effects of jitter:

Theoretical and Audible Effects of Jitter on Digital Audio Quality Benjamin, Eric; Gannon, Benjamin
AES Preprint: 4826 => these guys are from Dolby Labs so I suspect the work was thoroughly conducted but you never know. Certainly many audiophiles seem to disagree as they claim audible improvments when jitter is reduced from around 1 Nanosec to 200 psecs.

The AES paper concludes that 30 nanoseconds was the threshold of audibility on music....but specifcally designed test signals brought the threshold down to about 20 nanoseconds of jitter. They tried to use forms of jitter that are most easily audible - principally by minimizing the effect of masking (where a loud signal will mask a nearby frequencies at lower signal levels - jitter can be simulated to give the greatest frequency separation between the real audio signal and jitter induced distortion such that it has highest chance of audibility).

As I mentioned I am willing to test a solution if one exists for a few hundred....my jitter straight from my CD players must be around 1 nanosec (if specifications can be trusted). So I probably have what many would regard as levels of jitter that should be just about audible.

Having samples with jitter to compare would be meaningless unless the amount of jitter is quantified. Adding jitter to the point of making it an order of magnitude higher (nano seconds) than most decent players would not prove anything to me. Can anyone demonstrate that music through a cdp with around 300-400 ps of jitter as tested by stereophile would somehow gain astonishing resoluton by decreasing the jitter to say 100 ps as claimed by lessloss and the like? Does jitter get increasingly irrelevant as the sampling frequency is increased in the same player with a cheap clock, switching power supply and all?

I think a good A/B switching with zero lag would be the best way to hear jitter and describe exactly what it does to the sound

I can't do pefectly zero lag as the DSP amp takes two seconds to switch some pretty clunky relays - but this is close enough. I also would need to run it through my DSP amp as this has a multitude of inputs (toslink or SPDIF) and precise volume level matching capability. If the improvement cannot be heard through this DSP with AKM AK4382 192Khz/24 bit DAC's and a Crystal CS3310 analog attenuator and Burr Brown op amps then it is probably not worth the trouble as I would also need to upgrade this amp which is probably several thousand.

If I need to go to completely separate signal paths then it negates the possibility of A/B ing properly without moving and while seated at the listening position (with a remote in hand). If this were the case, then I am not really sure I could give up the convenience of the DSP unless the difference was truly impressive...

Shadorne - the jitter download is coming. It's in the works.

Steve N.

Shadorne, I like where you're going with this. I think your results would make a very interesting read, and I whole-heartedly support the experiment! I think a good A/B switching with zero lag would be the best way to hear jitter and describe exactly what it does to the sound, other than "de-vinylize" it.

Shadorne, I suggest speaking with Kyle at Reference Audio Mods 951-780-2869 about a Superclock for one of your devices. The SC4 retails for $300 and there are probably cheaper used or old-stock SC3s. I have no experience with budget players, but reportedly he has had decent results with Oppo and others under $500.

I suggest disposing of theory & gambling a few hundred dollars on a simple clock upgrade and report back to the forum.

What would you suggest that would be a few hundred dollars and would make an immediately obvious improvement? I have four mega-changers, a Blu-Ray player and some standalone CD players stacked in storage...I have more than enough gear to make a controlled A/B comparison from the listening position using a remote (if it is simply jitter correction). For a few hundred I would be willing to dispose of theory.

Amen Mrtennis.

My listening tests relating to the perception of jitter were gathered through four generations of clock upgrades within one CDP-- eliminating all other variables (except for cognitive dissonance), and disposing of all controversies regarding the quantitative measurement of jitter. A separate set of observations was formed through successive upgrades of DC power to clock, and to the digital sections of the player including motor/servo, PLLs, and LSI DSPs. This exercise led from simple stock 3-pin regulators, to sophisticated discrete regulator circuits, to batteries, to larger low-impedance batteries, to batteries with capacitance, to batteries with massive capacitance. To those entrenched in the "data is data" camp, I suggest disposing of theory & gambling a few hundred dollars on a simple clock upgrade and report back to the forum.

In the course of five years of developing the CDP, I've corresponded with perhaps a dozen amateur and professional modders who were all impressed(some to amazement) by the improvements associated with clock upgrades in otherwise respectable CDPs. There has been no criticism of the results of a clock upgrade.

Anyone seeking a more professional approach should visit Steve N's site, take a look at his Pace-Car product, note which clocks he uses, how he uses them, and how they are powered.

If you think that RBCD sounds synthetic or fatiguing or that the resolution of RBCD can't approach the musicality of vinyl, then you're probably hearing jitter.

if anecdotal observations are not taken seriously, what is the purpose of asking for advice to assist in the purchase of components ?

there are many threads on this and other discusssion forums asking for opinions on a variety of topics. the elicited opinions would be based upon the perceptions of audiogon members. if such perceptions are too be discounted as to their worth, what is to be gained from initiating threads whose basis is listening experience ?

Like some deleterious affects in audio, it may be easier to appreciate & to describe in its absence. Sometimes you don't know what you got till its gone. But dancing angels it most definitely is not.

Dusty,

I suspect jitter as experienced on most decent CD/SACD players sounds just like angels dancing on the head of a pin.

db

The question was WHAT DOES JITTER SOUND LIKE, and the conversation degraded into a brain battle of engineers

Sorry Dusty...the propellerheads do run on don't they...I'll take your advice and put some more scotch on the bridge of my glasses and go sharpen some pencils.

In the meantime - I believe there is a Stereophile Cd with an example of jitter.

In fact - it would be great if Steve or someone equally knowledgeable would put up a website with downloadable jitter examples...

Rotarius....THANK YOU!!

Over-clocked under-flow buffer bits blah blah blah blah...

The question was WHAT DOES JITTER SOUND LIKE, and the conversation degraded into a brain battle of engineers. If small amounts of jitter affected sound like small amounts of other distortions, then the above question would have a real answer such as could be given to the following questions:

What does mistracking sound like?
What does a ground-loop sound like?

These are things we can identify. Instead, we're arguing about whether we can even hear it or not, and the final answer (assuming it's something we actually can hear) seems to be "it sounds like less clarity." With an answer like that, you might as well be saying "ummmm... it just sounds worser."

I am skeptical about all this. To me, the biggest flaw is the sampling rate itself. A well recorded sacd can sound quite amazing even on a budget player with mediocre parts. The cd layer won't sound as good and is not as resolving with the same player. With all due respect Mr. Lessloss, removing a few pico seconds of jitter seems like polishing a turd. So what does jitter sound like? I am sure excessive jitter plays a role in masking detail to some extent but it sounds more like marketing hype backed up by "white papers".

"Isn't the buffer in a CD player designed to store data so that it can be processed/decoded to extract the relevant audio bit stream information so that only these "bits" can be sent to the output of the DAC?"

There is minimal buffering in most CD players, usually inside a controller chip that does the servo control to control the speed of the spindle. There is also a CODEC that decodes the data stream from the Pits, as well as read amplifiers etc..

"Aren't CD data (pits) stored in an error correction format called Solomon-Reed interleave code (not a straight audio bit stream) and therefore the clocking of data from the lazer pick up off the disc is NOT directly related to the clock that clocks data in to the DAC output?"

This is true, the frequencies are not identical, but related.

"Isn't there a separate timing required to control the buffer under-flow or over-flow (not clocked by the same clock that controls the DAC output even if the timing is obviously related as the buffer is ultimately suppling the bit stream)?"

The clock for this is created by PLL, so no overflow or underflow occurs. The Crystal oscillator sets the frequency for the spindle rotation, but there is "slop" in the frequency of the clock due to the PLL. The spindle rotation is not that precise, and the bits coming off the disk have a lot of jitter, so it must track this. There is generally a buffer that attempts to do a second PLL on this and reduce jitter, but it is usually not immune to the jitter coming off the disk.

"Since the buffer "buffers digital bits" then we don't have potential for jitter UNTIL the clocking out in the output of the DAC - or am I missing something again? In which case how does the buffer PLL affect jitter - is it induced noise on the power rails or some other in direct manner?

The secondary buffer output is clocked by a divided-down clock based on the bit-density on the disk (CD versus DVD for instance). In theory it is a fixed clock and should not be subject to the jitter coming off the disk, but unfortunately all of them are. Somehow, the chips that are used for these processes are imperfect, or the power systems are imperfect, so some jitter leaks through. It seems like this problem should have been solved long ago, and it has probably gotten better, but the problem still persists.

All you have to do is rewrite a CD to CD-R and listen to it on ANY CD player and you will hear a difference in a resolving system. Put a mat on the commercial CD and play it and you will hear a difference. Put a treatment coating on the commercial CD and you will hear a difference.

If these CD mechanisms worked ideally, then none of the above treatments would change the sound.

Steve N.
Empirical Audio

Shadorne - how do you think the data coming off the disk is stored in a buffer in the CD player without a PLL?

I'll take a stab at what I think is going on and you please correct me - I much appreciate your efforts/time to educate me. I apolgise if some of what I said is misleading - just trying toget my head round all this.

Isn't the buffer in a CD player designed to store data so that it can be processed/decoded to extract the relevant audio bit stream information so that only these "bits" can be sent to the output of the DAC?

Aren't CD data (pits) stored in an error correction format called Solomon-Reed interleave code (not a straight audio bit stream) and therefore the clocking of data from the lazer pick up off the disc is NOT directly related to the clock that clocks data in to the DAC output?

Isn't there a separate timing required to control the buffer under-flow or over-flow (not clocked by the same clock that controls the DAC output even if the timing is obviously related as the buffer is ultimately suppling the bit stream)?

Since the buffer "buffers digital bits" then we don't have potential for jitter UNTIL the clocking out in the output of the DAC - or am I missing something again? In which case how does the buffer PLL affect jitter - is it induced noise on the power rails or some other in direct manner?

If you have any suggestion for good books on this subject - let me know.

Shadorne - how do you think the data coming off the disk is stored in a buffer in the CD player without a PLL?

BTW, I am an EE. I was a design team lead on the Pentium II at Intel Corp. 30 years design experience designing everything from big disk and tape controllers for IBM equipment to massively parallel supercomputers to slot 1 processors.

Steve N.
Empirical Audio

digital jitter seems to smear timing quite differently and more objectionably so. Having progressed through four generations of clock in my CDP I can say that most of what listeners think is synthetic & irritating about RBCD relates to jitter.

Jitter has absolutely no effect on the timing of audio signals....you are misinformed. I suggest you read the book I referenced above rather than make conjecture. Jitter creates side bands or frequencies that are not in the original music - the closest thing to jitter would be IMD distortion - the side bands if big enough and far enough away from the main signal frequency (so as not to be masked) will be audible as non musical related distortion or a higher noise floor.

As far as jitter affecting timing in what you hear - this is impossible unless you are a super bat (I don't even think bats are that good)? Jitter is in the nanosecond and faster range of timing. No human has shown the ability to sense timing delays in this range... in this amount of time sound travels 11 millionths of a foot...there is just no way hearing is that good. Besides - the output filter in the CD players DAC removes frequencies above 22 Khz anyway....so any effect cannot be related to "timing" even if you describe it that way.

The reason I mention comparison between speed fluctuations in TT & digital jitter in CDP is because I experience these phenomena quite differently. As the speed stability of my TT has improved through various upgrades, I hear improved dimensionality, soundstage, bass control, dynamics, liveliness, focus, etc., even though pitch remains audibly imperfect. On this narrow point of pitch stability the CDP surpasses and I suspect will always surpass the TT (as evidenced particularly with piano music.) But somehow the ear is forgiving of even quite audible fluctuations in timing that originate in the analog domain. Perhaps this is because the physical locus of the stylus ensures that timing variations are applied uniformly across all spectra at each point in the LP groove.

In contrast, digital jitter seems to smear timing quite differently and more objectionably so. Having progressed through four generations of clock in my CDP I can say that most of what listeners think is synthetic & irritating about RBCD relates to jitter.

However, inaccuracies in the pit locations on the CD or CD-R contribute to the PLL clock jitter in the CD player

There is no PLL (Phase Lock Loop) used in a CD player unless it is getting its timing daisy chained down from some external device rather than its own internal clock (say an external SPDIF signal or TosLink signal, however this is not thee usual setup as youu are just using the CD players DAC).

Phase Lock Loops are used between devices in order to maintain synchronization ( for example a CD player and a DSP - the PLL in the DSP will keep in sync with the bit stream from the CD player - some PLL implementations can do a good job of reducing jitter )

Please refer to Page 207 of Nika Aldrich's book "Digital Audio Explained for the Audio Engineer" for an explanatin of a Phase Locked Loop (PLL). I strongly recommend this book to people unfamiliar with digital electronics (you don't need to be an EE to follow it).

Brownsfan - As I have said in other posts, it is the PRIMARY deficiency that makes Digital Audio fatigueing, and is the single most significant flaw in the S/PDIF and CD format.

Steve N.

"My point was that there is no jitter added or lost by copying CD-R's many times (provided everything remains in the digital domain). The same is true for digital processing - it adds no jitter. ONLY a jittery clock or jittery signal makes jitter."

I agree with all of this. However, inaccuracies in the pit locations on the CD or CD-R contribute to the PLL clock jitter in the CD player. This has been demonstrated thousands of times. There were even several products that re-wrote CD's to get improved pit placement. They work with every CD player I have tried.

Steve N.

Dgarretson - Wow and flutter exhibit the same results as jitter, frequency modulation, so the answer is yes, although some jitter occurs at rates and changes in ways that a turntable could not physically do.

Steve N.

Stereophile test CD # 2 contains an example of jitter. Based on that example, jitter is very, very bad and you don't want it! One would have to wonder if that might not be the largest contributer to listener fatigue in digital systems. Dgarretson's first post above is an apt description of what you hear in the test CD example.

Shadorne - you are missing the point.

I may have missed something but I think we agree apart from your claim "the positions of the pits in the CD are a form of timing information that can cause jitter as they are read", which is incorrect.

My point was that there is no jitter added or lost by copying CD-R's many times (provided everything remains in the digital domain). The same is true for digital processing - it adds no jitter. ONLY a jittery clock or jittery signal makes jitter. If A CD-R somehow makes life easier for a CD player such that somehow the CD players clock runs less jittery then it will play with less jitter (but this may linked to how warped the CD is or how well centered the hole in the CD rather than "timing from pit spacing", IMHO)

Audioengr,

From either a theoretical or experiential perspective, do you think the phomenenon of speed instability in a turntable is similar to digital jitter?

Bigamp - Sooner or later the folks that dont understand the jitter thing will hear it or they will eventually upgrade their systems to the point where they hear it. Until then, it is like trying to explain how the earth looks from space.

Jitter is simply inaccuracies in the timing of the bits that make up the data stream. It is like a clock that ticks every second. If the clock ticks at exactly each second time interval, then it is said to have no jitter. If some ticks come at .999 seconds and others at 1.001 seconds, then the overall time will be accurate over many seconds, but there is jitter in the timing. This is how actual real-time systems work. They all have some amount of jitter.

The effect of this jitter on the D/A conversion is to create frequency modulation in the analog output. This means that the point at which the top of the cymbol crash was supposed to occur actually occurs maybe 1 nanosecond later and then the trailing ringing of the cymbol comes maybe 1 nsec earlier. The rate of this change can be anywhere from 10hZ to 100kHz or higher. If there is only one sample that occurs at the wrong time, it will never be heard, but typical jitter signature is usually a constantly changing time error. This is why it is audible. The brain detects these things just like it detects moving objects with eyesight.

The time error has both amplitude and frequency or spectra characterisitics. Each CD player or computer audio device has different amplitude and spectra for its jitter, so they can sound very different from each other, even though the data is always the same. Data errors are very uncommon for both CD players and computer audio. Jitter is the difference that you are hearing, if you hear a difference.

Steve N.
Empirical Audio

Shadorne - you are missing the point. It is not the data in the copy that is different, as explained in the paper you cite. It is the jitter DURING real-time playback that is different. This is the distinction.

Steve N.

A lot of people still seem to not buy-in to jitter effecting sound. I get the impression people think that since their PC software loads fine from a CD without error, then their audio CDs should too. But it's different. Perhaps someone can explain what's happening in 10 words or less. Jitter occurs at different places-at the place where a cd is read and then between any (every) 2 points in the circuitry. Anyone want to take a stab at how this effects sound? E.G. "The edges of the bits are not square because of X, causing some 1s or 0s to get missed" or "The edges of the bits get fuzzy, causing the dac to approximate some bits.". Then there is latency jitter. I'm not saying either of these is correct, just giving illustrative examples. I'm no expert; looking for the experts to chime in.

Steve,

I woudl refer you to Nika Aldrich "Digtal Audio for teh Audio Engineer"

Quote:Page 353 "A digital recorder will store exactly the same information regardless of how jittery the clock"

Therefore according to Nika it makes no difference how many recordings or re-recordings or CD-R's you make.....ONLY a conversion to Analog or to Digital (where a clock is necessary) does jitter enter (from the clock).

Shadorne - the positions of the pits in the CD are a form of timing information that can cause jitter as they are read. How this affects the PLL/buffering in the CD player depends on the design of the CD player. It is evidently important though. Rewriting a disk on CD-R with low jitter is an audible improvement on virtually all CD players I have tried. I mod a LOT of transports and players, so I get to try many different ones. This is good evidence that the pit locations are actually important.

Steve N.
Empirical Audio

Shardorne, yes, you are right. I'm not too sure about the warped or uneven disc causing Jitter, though. My extensive experimentation shows that it is not this slow visible-to-the-eye movement of the lens which causes the Jitter one hears. Indeed, you can even put your finger onto a turning disc and you can cause a lot of low-frequency vibrations that way, but it isn't audible. What is audible then is if you go too far and cause a digital error. But Jitter itself is of a much more high frequency nature, as you say, such as from electronic oscillations and RF noise induction and the like.

Liudas

Liudas,

True. Physically Jitter can ONLY exist once there is some form of clock or timing device...so a CD cannot have any jitter, however, if there is difficulty for a CD player to read a disc then perhaps oscillations in the drive motor power or lens focussing power might somehow cause the clock to be in error or more jittery (say for example they share the same power supply which happens to oscillate due to lens motor fluctuations, as it struggles to read a warped or uneven disc).

Gonzalo,

In Digital copy generations, there is no more Jitter in the 2nd generation than there is in the 100th generation, since every time you repeat the loop you go back to the hard disc and all the Jitter that the laser added is again gone. Jitter only has meaning during the real-time ADC procedure or the real-time ADC procedure. Other than that, you can send Digital files to CD's, Flash Drives, up to the Mars Rovers and back again, and then burn your CD and it will have the same amount of Jitter if burned under the same circumstances as your first copy.

Actually, many people burn copies of CDR's because they are making a copy which is even BETTER than the original white CD, because after they burn it, the CD playback mechanism reads it (for various reasons) with less Jitter, given a signal to the DAC with less Jitter, which sounds better.

These various reasons include the substrate material, reflections, focussing, vibrational issues, etc.

Liudas

First off wantd to congratulate soem of our members here for their incisive and descriptive talents.
It has been propven without a doubt that Jitter is very perjudicial to our music, there was a test done in which a panel of well versed and auditioned audiophile and musicians listened for a litle while to a CD of first cut recording direct (to avoid missinterpretaions or wrong intent) then to listen to the same part of music but the 100th generation of recorded music on CD as well.
Same data, same bits no data error, same thing, what was the differnece between those two recordings?
you guessed it!!! much Jitter, not enough to trow you off but enough to sound degraded and lacking compared to the 1st generation recording, that point established i can tell by own experience that i have heard lossles compresion played on a Macintosh computer through a $150 USB DAC into a Audible Illusions modded preamp into Quicksilver Audio monoblocks into Vandersteen speakers sounded A LOT!!! better than a very good source of playing the same CD version going though a Benchmark media or Classé DAC going though the same pipelines.
So even though MP-3 is sonically inferior to 16 Bits also 16 bits are very rudimentary when compared to 24 bits 96 Khz or 192 KHz material.

That is my 2 cents here.
Losless compression might be the way to go for playback, still discs are required for portability and to take it to your car, boat, aprty or friends house ofr a listen to his/her new toys, etc.

Also when evaluating new components or speakers this still is the batter way to go.
Long like to CD's thank God DVD audio is here also. . .

God Bless!

gonzalo

Shadorne, Feb. Stereophile is one of the better issues in recent memory, with entertaining assaults by Atkinson & Fremer on the "MP3 as indistinguishable from CD" fiction propagated in the mainstream press. At the opposite extreme there are (finally) several less-than-superlative reviews of megabuck products (e.g. Escalante Fremont & BAT Rex.)

Of course you won't believe it, but RBCD on my tweaked CDP and vinyl on my tweaked TT run neck & neck. Making comparisons across analog & digital media raises the bar & can be helpful in measuring progress. MP3 sounds great doing an 8 minute mile on the treadmill.

Shadorne,
I know what you mean. There is a point after which it really is just a silly excess. I've had just as much emotional involvement with my music through the years of upgrades, as I do with my car system. ALl the upgrades have never changed my response to my favorite music. For me I have come to the full realization that it has (always)been more about a fascination/obsession with awesome hardware than as "the" medium to profound musical enjoyment. I have acheived what I think is a great "sound" but I could hear "Blue Sky" (ABB) or Beethoven's "Ode to Joy" on an AM radio and get just as passionate about it, as I do on a high dollar system.
I would argue that 99.99% of the audiogon community is also motivated by the same hardware obsession (why else are you here,eh?). Sure there is something to sitting in the sweet spot, in your space but that's all just initial conditions to the hardware equation. But it's all good, as I clearly prefer this to most other money sucking fascinations. TGIF.

The SCD-1 is different from some CDPs, insofar as a Synchronous Time Accuracy Controller (S-TACT) chip that is located next to DAC in the analog section of the player, isolates master-clock generation and signal voltage-pulse generation in one chip at a remove from noise propagated by high-speed operations in the RF & digital sections. The stock quartz oscillator chip is located in the analog section 1" from the S-TACT. In a clock upgrade the stock oscillator chip is removed & replaced by a lead-out to a 45Mhz clock PCB. To eliminate the possibility of noise induced by capacitive effects across the PCB, I lifted Xin pin of the S-TACT from the PCB and made short ptp connections between Xin & clock PCB. So in view of Sony's set-up that theoretically isolates master clock from digital noise, I am inclined to consider that audible improvement may be largely due to accuracy of the replacement clock.

I've heard audible improvements upgrading power to clock, and also after upgrading power and various passive SMD components around DSPs, PLLs, and motor/servo in the digital section. Whether this is due to reduced jitter or to reduction of other noise I cannot say. But I have no doubt that improvements in the digital domain other than clock are audible as well.

Esoteric sells an optional out-board clock for its top player that's accurate to a half part per billion; magazine reviewers claimed to hear a difference. I know a fellow in Japan who makes similar claims using an external pro signal generator to clock his player.

All this might sound like an exercise in diminishing returns but my ears tell me otherwise.

Needless to say, I take much of the claimed auditory observations with a grain of salt. Many theoretical differences that justify large expenditures do not conform with auditory reality.

Agree 100%! Large expenditures do NOT conform with auditory reality. This is why mildy compressed Mp3/AAC can sound pretty damn good or indistinguishable from uncompressed music!!

So of course explanations of the sound of jitter will be vague. After all, how many angels can dance on the head of a pin?

I agree again. However I would suggest that any audiophiles that claim to have seen Angels dancing (on a pin or otherwise) are not to be trusted concerning their other audio observations - especially when it comes to incredible claims of miracle improvements from their tweaks and/or upgrades.

Dgarretson: great example of a controlled experiment. I wonder how much the improved clock circuitry reduced radiated emmisions, reduced injected noise into the ground planes, vs the degree it reduced actual clock jitter.
I'll always have a hard time understanding why nanoseconds of clock skew difference matter in most modern cd digital receiver front ends. I mean the digital data is clocked off the substrate then buffered (fifo) in the main cd dsp; inside this dsp, a new clock is generated and sent across the interface to the DAC. This buffer is pretty much crucial to good cdp function. I don't understand how jitter, as long as the set up and hold times of the actual registers are met, can be any kind of problem. I have never done a clock mod; do they instruct the modder to cut the (typical) crystal clock osc and insert the new clock signal there? is this only one point or do they also handle the clock to the actual DAC.

Another key feature to modern cd dsp chips is that the actual word (or frame) is entirely jitter free. Perhaps one could argue if the jitter is so horribly poor that individual bits are mis-sampled as they are clocked into the DSP, (then the overall value of the word is off), but that would have be a seriously poor design. Personally too much marketing emphasis is placed on jitter, I feel. The standard approach by all high end cd player designs is to implement an off the shelf DSP device (the thing that sits very close to the spinning disc and is responsible for servo, and data sampling, as well as microcontroller interface) and an off the shelf DAC. Some play games intermediate stages to decouple clocks and reduce skew, but in the end it's really just designing with building blocks that have existed since the 80s. Jitter is one aspect to all this but I think its contribution to the overall distortion spectrum is very miniscule w.r.t. all the other links in chain from pits and bits to volts.
I don't doubt that anyone hears a difference from a mod, but it's hard to distinguish between REAL differences and perceived ones based on expectations (after all the time effort and money went into it there better be a difference right?!). Anyway these are my personal experiences. It's all good fun.

Shadorne,

Many decades ago my doctoral and post doc training was in psychoacoustics, particularly binaural processing. The concept of "critical bands" refers to a limitation of the resolution of the auditory system and the interaction of auditory stimuli. Needless to say, I take much of the claimed auditory observations with a grain of salt. Many theoretical differences that justify large expenditures do not conform with auditory reality.

From a telelogical perspective, our auditory system must be generalizer, otherwise it wouldn't serve us well. So of course explanations of the sound of jitter will be vague. After all, how many angels can dance on the head of a pin?

db

Still,....the above sounds like a Presidential Debate.

No real answers so far....hmmm...

I agree...it is all pretty vague. However in fairness there are infinite possibilities and (for those who bother to study this) that "masking" is a huge factor in our hearing ablity...and sounds in proximity to other louder sounds are often inaudible unless they are a fair distance in frequency from the loud sound (several octaves being a fair distance)....all of which means that certain forms of jitter may be much more audible then other forms with, for example, random jitter being quite benign (nothing to worry about).

Dpac996, these are my personal observations going from stock oscillator in my SCD-1, through three generations of Audiocom Superclock up to SC4. In each modification, only the clock (or the clock power supply) were changed. I installed each clock myself & made the comparison within hours of deinstalling the previous clock. There was immediate dramatic improvement, and further improvement over up to 200 hours of break-in. If this is just "going for it" then so be it. There is enough controversy about measured jitter that I'll go with the evidence of my ears on this one.

-Impossible to quantify unless you can tweak the actual jitter specs in the same DAC/cdp.
-If a designer has taken the road less travelled in reducing jitter to minimal levels other areas of the DAC/CDP (power supply, filtering, analog section, isolation) are highly likely to be well thought out and complementary.
Dgarretson, I assume you did this test and only changed the clock to a low jitter clock circuit, while leaving any other component unchanged. If so how did you do this? did you actually measure clock skew and spectral analysis pre/post or toss in a super clock look at the marketing specs and just go for it?

No real answers so far....hmmm...