OT: labelling CD/DVD disks

[Dotan Cohen]

On 23/10/06, Mike McCarty <Mike.McCarty at sbcglobal.net> wrote:
> > I'm not contradictining you, but recently I had a disk that was
> > scratched on the label side and would not read. I could literally see
> > through the scratch. I took a Black marker -Artline 70 - and coloured
> > over the scratch. Lo and behold- I could read the disc.
>
> This makes some sense, when you realize what is physically going
> on. CDROMs use forward error correction (FEC). When the number of
> bits in error on any given "track" are less than the critical
> number, then they can be corrected. What likely happened was that
> with a hole all the way through the metalization layer, the optics
> couldn't "see" the disc, and went into auto-focus, which caused the
> next bits not to be read due to being out of focus, effectively
> widening the scratch beyond the FEC capability to correct. Putting a
> backing on the disc may have made it so that the optics remained
> focussed, resulting in correctable errors.
>
> Mike

Sounds reasonable. I figured that I was helping it read the content
under the scratch.

Dotan Cohen

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