Home Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

Re: RE Error Rates and Jitter

Thank you for pointing out an error/typo in my web site page, I did not mean for it to read the way is does.

While it is possible for the read servo to be affected by jittered data, this is a tertiary or further down the chain type issue, and not what I intended to communicate.

[ I might accept that this could change the pattern of voltage transients caused by the amplifier for the laser pickup (and/or the input logic of the chipset), but there is no reason to assume these
transients would normaly be precisely in synch with the master clock (or out of synch, or perhaps larger/smaller in magnitude) than during a theoretical 'perfect' series of pits. ]

This is, I believe, the crux of the matter.

A clean pattern of PS transients vs. a jittered pattern of PS transients.

No, they do not necessarily correlate with a DAC or master clock timing transistion, but they will correlate close to or with some other sub section in the CD player.

Picture the entire chain of digital sub-systems within the CD player, and the fact that each one not only has signals within the subsection, but flowing to and communicating with other subsections.

Each time the signal passes through a logic gate, it is delayed slightly, and with enough of these hand alongs, you can get to a point, where the received data PS transient pattern coincides with ONE of these subsystems/subsections logic transition periods.

A jittered pattern will be able to overlap or coincide more easily, as it is spread out in time as far as where the overall coincidence points overlap. A jittered pattern does not have to coincide perfectly with another set of subsystem transistions, it only has to get near enough for the jitter to overlap the other gate firing pattern, and BINGO! that subsystem or subsection has just become affected AND EXTRA JITTER ADDED TO THE OVERALL SYSTEM, and now at a slightly different coincidence rate/frequency, etc. This can sort of cascade through the entire CD playback system, with each stage/subsystem adding an additional layer of jittered (on top of jittered) PS transient patterns, until there is a veritable constant buzz of PS transient patterns overlayed one on top of the other. This doesn't happen in complete isolation to just ONE CD subsystem/subsection, it ends up happenening to virtually ALL of them.

A CD playback system that is free from jittered PS transient patterns still has an entire series of overlayed transient patterns, however, since they are NOT jittered, they do not tend to overlap onto other subsystems/subsections nearly as easily, and hence, the whole domino chain of PS transients does not get goosed as much. It may be as much as an order of magnitude lower in overall trash at the DAC.

Since one of the things that a high end CD player or DAC does, is to beef up the PS, and it's resistance to allowing these transients to propogate through the system (independant transformer windings, regulators, etc.), it tends to reduce the generation and propagation fo these PS transient paterns, and their cascading through the entire CD playback system as a whole.

A CD playback system that has jitter interacting with ALL portions of the CD playback system via the various subsystems and subsections vs. one that is a totally clean non-jittered CD playback system, has a world more timing 'fuzz' riding on it's PS rails, and hence, the DAC is exposed to a lot more potential timing errors as it attempts to clock out the data precisely.

That is what I am talking about.

Jon Risch
Jon Risch


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