Can CD's deteriorate by LASER ROT?

The old CDs I mention not only got noisy with age, the tracks would sometimes be unreadable, ie, when the disc is inserted, the transport spins, but cannot find the tracks, so the CD will not play. If play is pressed anyway, the CD will spin but never start playing.

I was a CD early adopter (oh the shame!) and have a number of first issue CD's from 1983. None show any signs of deterioration and play just fine today (boy has CD sound come a long way!).

I also have a number of laserdiscs, and a number of these do show signs of laser rot, which as Sugarbrie notes appears as colored snow in the picture.

On laserdiscs the picture is analog composite video while the audio appears in both analog and also in digital form (on most laser discs). Thus picture quality directly correlates with the disc condition.

CD's are different, though. The digital data includes powerful error correcting codes in addition to the raw music data. This ECC code, which includes redundant data, allows the player to recognize almost all damaged data reads and to perfectly correct most of them. If the player cannot restore missing data bits from the ECC code, it attempts to interpolate the missing data (error concealment). If the data gap is too great for this, the player mutes.

Note that error correcting codes are also used to keep your internet traffic error free.

To increase the probability or error correction, CD data is not recorded linearly bit-for-bit along the pit tracks (i.e., not like music in a record groove). Instead data is written discontiguously in small blocks specially encoded to make the player's reading job easier. The player maps these "symbols" back into data words, then reorders the discontiguous data stream into the original 44.1 khz bit stream (for each channel!).

This discontiguous recording means that local disc damage will affect small data blocks from separate parts of the original data stream. Such damage is usually easily corrected by the ECC codes and unlikely to result in error concealment.

Sony/Phillips assumed that all discs would contain manufacturing imperfections, dust and minor surface damage. Thus a CD's sound does not degrade in proportion to disc damage or flaws.

Up to a certain point deterioration produces no effect on the CD's sound. After that only certain portions of the disc with especially heavy damage would show ticks or pops as error concealment takes effect. At worst case the disc would skip in spots or stop playing.

I'm not sure how Sugarbrie gets the increasing noise levels on old CD's.

had this info tucked away pertaining to DiscoVision LDs
LaserRot:
Cause: Various
After some in depth research, my stand on LaserRot and DiscoVision has changed. LaserRot is a term coined during the early 80s as a way to describe a LaserDisc, that upon purchase, played very well, but then over time would develop video speckles and possibly audio noise. From the beginning, DiscoVision engineers struggled to determine why the quality of the discs were failing. Product would leave the warehouse having been quality checked only to be purchased by a consumer and returned as defective.

The gamut of defects due to laserrot vary. Some discs have developed light speckling at the beginning or the end of a side. Some sides develop a speckling pattern which stays constant through the entire length of a side. Still others deteriorate to the point that there is no visible picture at all and the audio is just a jumble of frequencies that doesn't even qualify as static.

The original statement made here DiscoVision discs do not rot is not true. Part of what has been discovered is that the discs did rot, but they would reach a rot threshold and the deterioration of the discs would stop. Some believe the discs would rot during the discs "curing" period - after which the level of rot would not increase. This is relatively far fetched because many discs would show the tale-tale signs of rot several months after purchasing.

That said, rot on DiscoVision discs is not progressive. Enough time has passed that any rot to develop on the discs would have done so by now. It's safe to say that the condition of your discs at this late date is the way they are going to stay when properly handled.
for what its worth. kurt

Laser Rot was common is early CDs and Laserdiscs. I do not know what caused it, but it does not seem to occur much if at all anymore. I would not be surprised (speculation) if there is a possibility of Laser Rot eventually with CDRs, considering how they are made (on your PC).

I still have a couple old CDs and Laserdiscs with Laser Rot. They laserdiscs have snow like a bad TV picture and sometimes dirty sound. The CDs have background noise like a dirty LP or that background noise heard on old 78 RPM records.

There are obviously different levels of intensity on lasers or any other form of energy. With that in mind, don't you think that the plastic would melt / become deformed before it could actually soften / distort the aluminum disc ???

I think that we can call this one a "hoax". Especially since most lasers "deteriorate" or "get weaker" as they age. Sean
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