What does Jitter sound like?

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).

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.

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).

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 - 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)

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).

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.

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.

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...

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.

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...

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.

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..