How many forms of Jitter can you identify?


Just a few days ago I was read about a clock upgrade for a CD player that was said to reduce jitter by having a more accurate clock. Today, I'm reading about a Mikrosmooth CD polishing kit that claims to reduce jitter.

I'm absolutely positive that it isn't possible to apply a product to a CD that will have any effect on the digital clock on the CD player. I'm also skeptical that it can make any difference in how the CD player spins the disk so how does it reduce jitter? At most it should a good cleaning product that could allow the laser to read the disk better eliminating any error correction from being necessary.

What am I missing?
mceljo
There is a good summary of ten potential contributors to jitter in this paper by Steve Nugent of Empirical Audio, about a third of the way down the page.

Note that items 2 and 3, which pertain to the pits on the cd itself, and the electromechanical systems that spin the disk and read the data, are "not an issue ... for newer players that completely buffer the data at high-speed from a CDROM reader to a memory buffer."

IMO, assuming everything involved is reasonably well designed, by far the most major contributor to jitter is the S/PDIF or AES/EBU interface that is commonly used between source and dac. Making the timing that is applied to the dac chip itself ultimately dependent on a clock supplied by a different component, which is multiplexed together with the audio data into a single signal that is then transmitted between components, the clock subsequently having to be extracted from that signal, is an inherently compromised concept IMO. Several different items in Steve's list, btw, pertain to that interface.
At most it should a good cleaning product that could allow the laser to read the disk better eliminating any error correction from being necessary.
Assuming the player is reasonably well designed, error correction is not an issue, because it results in bit perfect recreation of the original data. An issue only arises when the data being read is so badly messed up, for instance due to a severe scratch on the disk, that the errors cannot be corrected. In that case error interpolation, or conceivably outright muting, will occur, which will affect sonics as it represents an approximation at best.

Best regards,
--Al
Well, shortly after I clicked "submit" I came to the realization of my "senor moment" when I totally forgot about the buffering that completely eliminates any possibility of jitter being generated by pit/land reading itself.
What can I say, I wish I could withdraw my post.
But since that's not possible, here I am again, standing corrected and humbled by Al's perfect answer.
The worst forms of jitter are non-random (by far)!

If a disc wobbles while it spins then this may cause cyclical adjustments to the pick up laser servo and these repetitive draws on power may induce variations in the clock through the power supply.

IMHO, the most accurate or reliable approach is an asynchronous setup where the output clock is not synchronized to the input.
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I'm absolutely positive that it isn't possible to apply a product to a CD that will have any effect on the digital clock on the CD player. I'm also skeptical that it can make any difference in how the CD player spins the disk so how does it reduce jitter? At most it should a good cleaning product that could allow the laser to read the disk better eliminating any error correction from being necessary.

What am I missing?
Mceljo

not true! Shadorne has hit upon the correct explanation altho' he gave yet another cause for jitter creation:
If a disc wobbles while it spins then this may cause cyclical adjustments to the pick up laser servo and these repetitive draws on power may induce variations in the clock through the power supply.
That's why that they have disk cutters (which re-cuts the outer edge of the disk with a sharp knife so as to smooth it & reduce/eliminate disk wobble).

You get the same random/spikey draws of current from the power supply when the laser light (trying to read the disk) reflects at funny angles off a dirty disk & after repeated reflections inside the laser transport box reaches the optical reader circuit. These multiple reflected rays of light are not the data from the disk but the optical reader knows no better & there are draws of current from the power supply as it tries to read this "data".
A power supply with lots of glitches tranfers these glitches to all the circuits are it is powering. So, in EE parlance we say that amplitude modulation (AM) on the power supply has created AM & PM (phase modulation) in the circuits being powered by that supply. Both AM & PM create jitter in the digital (music) signal being processed. This is one of the reasons you see multiple supplies in digital (CDP, transport, DAC, re-clockers) equipment & often it is prominently advertised. They are trying to prevent one corrupt sub-system from corrupting another...