Most of CDPs play in real time - there is no time to read particular sector again. Ripping program can access each sector unlimited number of times to obtain right data (proper checksum). Car or portable CDPs have to make up time to be able to return to troubled (bump) moment/sector and reread it. In order to do this CD is rotating a little faster than necessary and the data is buffered. I had once Panasonic portable CDP with a switch to enable/disable this mode. I could clearly see thru the window CD rotating faster in bump-proof mode. I'm only not sure what is considered a "bad data". Reed Solomon code allows not only error correction up to certain number of missing data point (2.5mm scratch along the track per Al's post), but also data interpolation for a little longer scratches along the track. CDs in really bad shape might still play fine, but a lot of data will be interpolated. Ripping program can obtain right data to create new CD-R with better sound than original scratched CD. I was even able to save that way few completely unreadable CDs (but it took long processing time).
Theoretical question about how CD's work
Theoretically, can the contents of a CD be printed out onto sheets of paper in 1’s & 0’s, re-entered digit by digit (say, by a generous helper monkey with an infinite lifespan) into some sort of program, and the same sound will be replicated? Just trying to understand how CD’s work (though I’ve been trying for 25 years and it still seems like magic to me).
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almarg IMO the reason many of the tweaks mentioned above by Geoff may be beneficial in some situations has nothing whatsoever to do with bit errors or error correction. The main reason in most cases is likely to be related to electrical noise generated by the servo mechanisms and circuitry in the transport part of the player, as it tracks the disc, coupling into unrelated downstream circuitry in the player, causing jitter in the D/A conversion process, and/or intermodulation or other effects on the analog signal path. The degree to which that occurs will be dependent on the design of the particular player, of course, as well as on the condition of the disc. >>>>Uh, I never said all the tweaks I mentioned affected bit errors or error correction. The ones I am pretty sure I can prove affect bit errors and error correction are New Dark Matter visible and invisible stray light absorption tweak, damping the CD (my Mystery Tweak) and coloring the CD, which absorbs visible stray light. Also, vibration isolation. All of those are my tweaks. The demagnetizing of CDs and elimination static electric fields ON CDs is anybody’s guess. I don’t think anyone has explained them, at least not to my satisfaction. note to self - I hate to judge before all the facts are in but it appears the Skeptics (capitalized for almarg’s benefit) would rather fight than switch. It certainly would not take a neurosurgeon or rocket scientist to do a little investigation and try to get to the bottom of these things. Isn’t investigation a primary part of the scientific method. And what about curiosity? Isn’t that part of the scientific method? Apparent it’s all too much trouble. |
erik_squires I love that the OP has orphaned this thread, but people are still arguing about how CD’s work. :D :D :D Yeah, I’m starting to think it might have been a drive by. 😬 |
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