Scratched cd's?


#1

Question… I put a cd into my PWT today with a known scratch on the disk. On other CD players that I have owned,when the part of the cd that is scratched is being read by the player it will skip around a bit and then continue to play. When I played the same track on the PWT it just stopped dead in its tracks and would not budge any further. Is there a remedy for scratched CDs with the PWT? Does this happen because of no error correction and/or because of the memory drive not being able to cope with the problem?
Thanks…Mark


#2

CD players cope with physical flaws to different degrees, depending on many factors including the transport used and the error correction algorithms employed. The PWT is quite sophisticated in its read until correct approach and error recovery. But it appears the PWT is not happy addressing the specific conspiracy of circumstances present with your disk.

I assume you are aware that any plastic cutting compound and polish will easily repair the scratch. It is easier than removing a scratch from a motorcycle visor or automobile gauge cluster.


#3

Thanks Elk for the reply. I have already used a scratch compound on the disk,and that process worked for my other players. My question is in more concern as to whether or not the PWT is capable of reading disks that may have a (specific conspiracy of circumstances…generally speaking). ie; can the memory drive in the PWT adjust for scratches or dropouts on a disk or not.Would it be a stretch to think that the memory drive is not capable of filling in the blanks through the PWT’s error correction,hence,a dead stop without recovery.

Does the PWT even have error correction on board? I thought I read somewhere that it was not needed because of the memory drive being utilized.


#4

My understanding is that the PWT does not employ the lossy error correction schemes found in the typical transport. Instead, its error correction method is to reread the disc until the data is complete.

If there is a hole in the data which cannot be filled by a Redbook CD’s data redundancy format, such as on your disk, the PWT will not guess as to what should fill the hole. This must be why you are having issues with this particular disk.


#5

Thanks Elk. I think that might be the answer to my question. The PWT can only read to memory and not employ the lossy error correction that you speak of.


#6

The PWT does more than simply read to memory. Instead of relying on predictive error correction which guesses at the missing data, it instead rereads the disk until it captures the actual datastream.

Of course, there are limits. If all redundancies of the data are missing - such as in a seriously damaged disk - the PWT cannot recover the data no matter how many times it tries to reread the disk and it stops trying. It is smart enough to know to stop beating its head metaphorical head against the wall.

Personally, I find this more appealing than reading once and applying predictive guesses for the missing and corrupt data.


#7
Elk said The PWT does more than simply read to memory. Instead of relying on predictive error correction which guesses at the missing data, it instead rereads the disk until it captures the actual datastream.

Of course, there are limits. If all redundancies of the data are missing - such as in a seriously damaged disk - the PWT cannot recover the data no matter how many times it tries to reread the disk and it stops trying. It is smart enough to know to stop beating its head metaphorical head against the wall.

Personally, I find this more appealing than reading once and applying predictive guesses for the missing and corrupt data.

All makes sense to me Elk. Thanks for your answer.