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Possibly because a cheap player has poorer error correction?

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caspian@peak.org

In Reply to: RE: I think this may be more effective on a cheap CD player posted by Metralla on July 04, 2010 at 10:56:45

When this tweak first came along, the owner of the local used record store tried this on several discs. Another clerk and several customers all heard distinct differences between greened and ungreened copies of otherwise identical CDs, to the extent that after several comparative auditions, we could reliably tell "blind" which was which. This was on the fairly low end store system. Nobody could decide if it constituted an "improvement," but we definitely heard differences. On my Rotel player at home, I couldn't really hear much effect.

The "theory" is that greening the edges absorbs some of the red light being refracted around inside the polycarbonate layer, thus reducing the amount of spurious data read by the pickup. But perhaps a player with better error correction can reject more of the spurious data?

Follow Ups:

RE: "But perhaps a player with better error correction can reject more of the spurious data" - geoffkait 14:56:54 07/10/10 (2)
You may find it interesting that the error correction algorithms do not correct this type of error. The error correction codes were developed to correct for "predictable" errors such as fingerprints and scratches. "Random" errors such as those produced by background scattered laser light go uncorrected. Since this particular problem is virtually unknown by manufacturers, the problem remains, even in high end players. The scattered laser light is everywhere inside the player, not only in the polycarbonate layer. The photodetector will "detect" any signal that is greater than about 70% of the "real" signal (reflected from the metal layer).

Edits: 07/10/10
- RE: "But perhaps a player with better error correction can reject more of the spurious data" - rick_m 07:35:35 07/18/10 (1)
  "errors such as those produced by background scattered laser light go uncorrected"
  
  I don't think so, you almost never get a C2 error. Far more likely in my book is that if reflections are a problem the mechanism is secondary, perhaps modulation of the photodetector circuit's slicing point or additional work by the focus coil somehow coupling into the works.
  
  It would be interesting to hang a current probe on the focus coil and see if that correlates with anything heard.
  
  Rick
  - RE: "It would be interesting to hang a current probe on the focus coil, see if that correlates with anything." - geoffkait 10:58:33 07/18/10 (0)
    Hey, I just report the problem, everyone is free to offer their reasons. Everyone is also free to test to their heart's content. Are you volunteering? Get rid of the scattered light and double the performance. What's wrong with that?

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