How many forms of Jitter can you identify?

07-19-11: Ericjcabrera
my buddy has a furutech demag that we use in addition to cleaning discs, and both of us, on both of our systems, can hear sonic improvements, sometimes significant on some cd's. how demagnetizing cd's affects player performance is beyond me, but i do know it works.

the CD disk is made of plastic & some organic dies that hold the digital data. The plastic structural material is not non-magnetic. Thus, when the laser light hits the plastic underside to read the data, over time the plastic gets mildly magnetized. For example, how many times have you experienced plastic packaging material "stick" to your fingers due to electro-static charge on it??? I'm sure many times...
The de-mag unit un-does this magnetization so that there is minimal/zero interaction between the mild magnet that the CD disk has become & the magnets inside the laser transport box.

The CD disk is made of plastic & some organic dies that hold the digital data. The plastic structural material is not non-magnetic. Thus, when the laser light hits the plastic underside to read the data, over time the plastic gets mildly magnetized. For example, how many times have you experienced plastic packaging material "stick" to your fingers due to electro-static charge on it???

Bombaywalla, I'm not sure I follow that. Static electrical charges and magnetization are two different things. And why would exposure to light cause either one?

Good point by Shadorne. Seconding Bombaywalla's comment about that point, it should be kept in mind that the extent to which that effect may be significant will be highly dependent on the design of the particular component.

Best regards,
-- Al

Bombaywalla, I'm not sure I follow that. Static electrical charges and magnetization are two different things.

Al, it true that these are 2 different effects but they are interactive & influence each other. Static electric charge does create an electric field around it & this electric field can be/is influenced by magnetic materials used inside the transport box. Over time some of the magnetizm is transfered over to the CD disk (just like when you keep a ferro-magnetic material that is not originally a magnet in contact with a magnet over a longish period of time that ferro-magnetic material becomes a weak magnet).
(I'm sure that you'll agree that static charge does create an electric field around it).

And why would exposure to light cause either one?

the laser light is highly focused beam of photons impinging on the CD with very high intensity. Over time this will transfer electrons (or bleach electrons) to mildly charge the underside of the disk one way or the other. Then we are back to the above argument about statically charged CD disk being influenced by the magnets inside the transport box....

There is yet two other items that will mildly magnetize the CD disk that I did not touch upon earlier - (1) the inks that are used to print the CD label contain ferro-electric substances like iron-oxide (FeO2) & (2) the impurities in the Aluminum used to create the dye. You can read more on the Acoustic Revive website as to what A-R think about this topic. Here is that website:
http://www.acoustic-revive.com/english/rd3/rd3_01.html

Bombaywalla, thanks for the explanation.

The logical follow-up question would be how significant is all of this from a quantitative standpoint? The data on page 3 of the reference you provided addresses that question, although the various terms and quantities are not clearly defined. My interpretation of it is as follows:

1)Looking at the first two of the four tabulations, on average there were 0.00 uncorrectable errors in each 1 second block, both before and after demagnetization.

2)Looking at the last two of the four tabulations, the WORST CASE (across some unspecified number of disks, trials, etc., and averaged in some way) was that there were 0.22 uncorrectable errors per 1 second block, or in other words 1 interpolated sample approximately every 5 seconds (which would comprise approximately 450,000 16-bit samples for the two channels).

And what they are saying is that demagnetizing would reduce that worst case number of interpolated samples by about one-third.

The bottom line on audibility, IMO: I'll give it a "definite maybe," but from a personal standpoint I don't consider any of that to be sufficiently compelling to inspire me to go out and buy one.

Best regards,
-- Al

Al, no problem.

yeah, it's hard to say how quantative this particular effect is. It is a mechanism of jitter generation & it might not be significant in & of itself but combined with all the other hash in the signalling chain, it probably does contribute to the overall digital nature of CD playback.
In the A-R website they did show some plots of amplitude of wanted signals increasing after de-magnetizing & their claim was one could hear sounds not heard before during playback. Never tried one myself so I cannot comment but they are showing data to that effect.....
So, like many things - best to attack the jitter issues by addressing the largest perpertrators leaving only the minor contributors to be attacked some later day time &/or budget permitting.