Questions about disc degradation

vbimport

#1

Hey, All,

Thanks to this site, I’m learning about the ‘nuances’ & complexities of disc burning. And I’d like a little education about disc degradation.

Assuming high quality media is used, how big of an issue is disc degradation? I guess I’ll break that question down into some sub-questions:

  1. I’m curious about what exactly happens to a disc (CD or DVD) that results in “degradation” over time. I remember when CDs first came out (1982, IIRC?) the consensus was that optical discs could very well last a lifetime or more. You have a metal substrate sealed by a clear plastic coating, and the data is encoded in microscopic patterns burned into the disc surface, so what can “go bad”? The patterns aren’t going to move or change shape, are they? And as long as it’s not scratched & exposed to air, the substrate won’t corrode or oxidize, so … Again, what goes wrong? (I’m excluding obvious things like subjecting the discs to abuse.)

  2. Generally speaking, which are more prone to degradation – CDs or DVDs? And why?

  3. This is kinda related to Question 1, but what goes wrong with a CD to make it “develop” more C1 errors over time? Or develop C2 errors when there weren’t any when the disc was originally burned/created?

  4. I was a teenager and a huge music fan in the mid-80s when CDs first came out, and to this day, every one of the CDs I bought back then still plays flawlessly. Since they’re ~20 years old, how can they still work perfectly if CD degradation is a ‘real’ issue?

  5. Are commercial DVDs more or less prone to degradation than the ones people like us burn on our computer burners? And why?

  6. Again assuming high quality media is used, is there any kind of “rule of thumb” amongst experts about how often a person should make fresh copies of their self-burned CDs & DVDs and discard the old ones? Every 2 years? 3 years? 5 years? Or is the answer simply, “Scan them every few months and make new ones as soon as errors start developing”?

Heh heh … that should make a good start. :stuck_out_tongue:


#2

Burned DVDs are much more susceptible to degradation. Commercial DVDs are indeed pressed metal, but recordables use a dye. Commercial DVDs are much more durable. Dyes are less stable over time.

A number of things other than dye failure can happen to discs too. If they’re stored in too humid of an environment, they can start to rot. The glue bonding layers together can start to fail. Even gravity can start to bend them if they’re stored horizontally. As you play them, they’re degrading, because it causes heat. Heat hastens chemical reactions/degradation.

A good rule is to store any important data on more than one medium, such as a HDD. Failing that, scan the discs for errors every 6 months or so. The ECMA standards are <280 PIE maximum and <4 PIF maximum. When the scans start reporting more than that, it’s time for a re-burn.


#3

Well I can’t agree that pressed DVDs are better than blanks, because I’d be a rich man if I had a dollar for every original pressed DVD with streaks, or funny looking defects on the recording side. Plus I’ve also read about plenty of people with original DVDs rotting.

I’d trust my verbatim blanks over a pressed disc any day. That may just be my opinion but I’ve seen, read and heard too much about people’s original discs degrading to trust them more than a good quality burnt disc.

Now whether CD-R or DVDR lasts longer, no one truly knows or has any [B]real world[/B] proof to show which one lasts longer. All I know is that my TY and Verbatim DVDR and CD-R all work fine. None degraded, whether they be CD-R or DVDR. DVD is more durable, so I trust that more for durability.

  1. I was a teenager and a huge music fan in the mid-80s when CDs first came out, and to this day, every one of the CDs I bought back then still plays flawlessly. Since they’re ~20 years old, how can they still work perfectly if CD degradation is a ‘real’ issue?

Well, it’s a real issue since it [B][I]can[/I][/B] happen and all your music could be lost. But in your case, you must have got some well made CDs and you probably stored them fairly well also. Therefore you have not really seen any degradation and hopefully won’t for a long time :slight_smile:

  1. Again assuming high quality media is used, is there any kind of “rule of thumb” amongst experts about how often a person should make fresh copies of their self-burned CDs & DVDs and discard the old ones? Every 2 years? 3 years? 5 years? Or is the answer simply, “Scan them every few months and make new ones as soon as errors start developing”?

It’s up to you really and how much you trust your media, how important it is also etc. I personally like to make a backup of my original discs once every year or two, just to be sure. Plenty of people also give good advice which is to backup things onto different discs, maybe one copy on a TY, another on a Verbatim, then one on the hard drive as well. There’s no point in making two backups onto two verbatims from the same spindle, if one degrades, chances are both will and most likely at a similar time.

Hope that helped a bit :stuck_out_tongue:


#4

Make 1 or 2 extra copies and check them every once in a while. Good dvdr discs i used with decent burners 4 years ago are still very nice. Only my LiteOn 411 & 811 made a mess of almost everything.

Extra copies doesn’t cost a lot and if the data is important i suppose it’s worth it :wink:


#5

I started buying CDs in 1984, and I’ve got CDs as old as from 1983.

I have ripped all my Audio CDs to my pc (in high bit-rate vbr mp3 format) so I have tested the actual readability of all those discs. Out of roughly 700 CDs there were 2 CDs that were extremely difficult to copy perfectly and 1 CD where I couldn’t copy it perfectly but had to settle for a copy with inaudible errors.

So the problem is real, but the percentage of degraded CDs is low and if your assertion that your CDs “work perfectly” is based only on playing them in your CD player, then it’s possible that some of your CDs have actually degraded but still sound OK because of the error-masking capability of CD players.


#6

Completely agree. I make two additional copies of anything I burn, making 3 sets in total, although you may not want to go that far :wink:

I still have the first (DVD R) burns I made, on an LDW-851S on Panasonic branded TYG01 media. :slight_smile:


#7

Do You guys also scan your pressed DVDs? Some people put down those
familiar marks on the DVDs as “rot” but I see those on discs fresh
out from the factory so it’s not something that would appear over time
(it’s gluemarks,I presume).Nevertheless,I also have heard some disc gone
bad but it was in regard of one or two distributor and their printruns (Anchor
Bay is one of them).


#8

I don’t usually scan my pressed DVDs. When I rip them, they all usually go at full speed which means they are at least readable. Even if the error rates are higher on a pressed disc, it’ll still be easier to read than a burn because of the low jitter and high reflectivity.

Oh and yes the marks I speak of are from discs that a brand new. Whether they be PS2 games or movies, I’ve seen plenty. Not sure if they are safe, but only time can tell if those spots degrade faster than the rest of the disc, if at all.


#9

[B]Ken in California:[/B]

  1. I assume you are referring only to pressed discs? An excellent source of information on the questions you have asked is Media Sciences who have published several FAQs on CD/DVD longevity.

http://www.mscience.com/faq30.html

  1. DVD media is more prone to degradation problems in longevity testing and I would agree with that based on my own experiences. Primary reason is that DVD media seems more susceptible to moisture IIRC.

  2. http://www.mscience.com/faq31.html
    http://www.mscience.com/cdrfail.html

  3. If you are comparing a pressed DVD which has been well manufactured versus a well written/well manufactured recordable DVD, then IMO, the pressed disc will last longer as all write-once recordable DVD is based on organic dye which will eventually degrade.

  4. I would take the simple answer, though it is the most potentially time consuming (as you would be using media with generally good stability characteristics).


#10

Thanks for all the feedback, everyone. I appreciate it.

I just have one more question:

I’m not clear on the difference between pressed (pre-recorded commercial) discs and the blank discs we all use in our computers.

Some of you guys have mentioned that the blanks use organic dye, which can/will degrade over time. Is the dye layer the place where data is recorded onto? When I first learned a bit about optical discs way back when (early 80’s), I think I remember reading that the data was encoded onto a metal substrate. Is that accurate, and do the blanks we use have an organic dye layer, rather than a metal substrate, on which data is recorded? Is that the difference?

I realize this question prolly would have been more suited for Newbie forum, but since we’re already on the topic in this thread, I thought I’d go ahead and post it here.


#11

On blank discs the only thing stamped into the disc itself is the pregroove which the laser follows when writing (this also contains information such as the disc manufacturer and writing parameters for the burner). The reflective layer is covered with a dye which the laser burns marks into.


#12

In order to be burnable in the first place, burnable media has to have a surface that can be changed. This is a dye and it is changed with heat from a laser. Because it can be changed with heat, it isn’t perfectly stable and over very long periods of time it will change. This can cause read errors down the road.

Pressed DVDs and CDs are not changeable - they are physically manufactured with the data present in an unchangeable form - and therefore do not need dyes that can degrade with time. They can delaminate (physically come apart) but if they are well made, they should last essentially forever.

The only way to get truly permanent DVDs and CDs is to get them pressed. Burned media is never going to be as good as pressed media. It’s awfully good, but it can never be as good.


#13

Sound nice on paper, but sadly the materials used can also rot and degrade in some way. Dye unstability is certainly not the only cause of disc degradation. :disagree:

Just like cd pirate, I’ve had a couple of commercialy pressed DVDs developing reading issues after a couple of years. Notably WB titles… and I certainly went mad when my “A Clockwork Orange” and “2001 a space Odyssey” discs started stuttering an freezing… (before you ask, no scratches, no dirt). :a


#14

That’s true. :slight_smile: That’s usually due to delamination… but it is possible for a pressed DVD or CD to fail.

Burned media can fail in all the same ways, plus a few more.

I’ve actually never had an original CD or DVD fail. Perhaps I’m lucky.


#15

Thank, Jim. So what kind of ‘surface’ is the data burned into? If it’s not dye like with blanks, what is the material?

And while we’re at it: Since the dye in blank discs is “changeable” with heat, has anyone ever tested longevity/reliability of discs stored in a refrigerator? And just how much heat would typically be required to change the dye characteristics and actually alter or degrade the data encoded on it? Would just using the discs in a desert or tropical climate be hot enough to do damage, or would it require really high temps like those generated by a laser?


#16

Yes you are lucky :stuck_out_tongue:

I’ve not only seen pressed discs degrade. I have had some which didn’t even work to begin with. Talk about poor quality control.

I’ve also seen quite a few rental DVDs and games that have cracks in the centre hub which simply increase in size every time they are removed and placed back in the case. I wouldn’t even dream of putting those cracked discs in my PC to watch, since once the drive spins up… it could very well go boom :stuck_out_tongue:


#17

Do you realise what you’re asking? I mean the time factor: how many years would it take to test this? :bigsmile: LOL - most of my discs stored at room temps don’t show any change in PIE/PIF figures after two years, so how (I should say [I]when[/I] ;)) could I compare their (unmeasurable) degradation rate to the one of discs stored in a fridge? :stuck_out_tongue:

Maybe by using the fastest degrading discs on earth CAUGHRitek G05CAUGH, burning 20 of them, putting 10 in the fridge and 10 at normal room temps? Mmmhhh… not even sure that the results would be of any interest. Funny, sure, but no generalization could be done about discs in general as these are a very special case. :bigsmile:

And just how much heat would typically be required to change the dye characteristics and actually alter or degrade the data encoded on it?
Very variable depending on the disc model and the humidity levels! You really want numbers? A rough answer could be: avoid temps >30°C.

Manufacturers claims about media longevity are for storage <~30°C and <~50% humidity.

Damage done by “normal” elevated temps (not talking about cooking the discs here) is gradual, depends on other factors (humidity is the main one) and as I said before different from model to model, even from disc to disc. There are no existing clear answers to your questions. :frowning:


#18

The surface on a pressed CD or DVD is aluminum or (rarely) gold, and the actual bits of data are physically impressed upon the aluminum.

With burned media, there is a reflective layer of aluminum (usually) or gold (rarely). Above this is a dye. The dye is burned, or left alone, to simulate the physical pressing of the metal on pressed discs. A burned bit is the same data-wise as a depressed bit. Unburned bits are the same as undepresssed bits.

As for how much heat would degrade a disc, there are too many variables involved to permit a straight answer. Very high quality media (e.g. Taiyo Yuden) might tolerate very high temperatures for prolonged periods. Very cheap media might be very intolerant of any high temperatures at all.

Remember, too, that all CDs and DVDs (even pressed originals) have errors. There is built-in error correction in the data stream that permits error-free recovery the vast majority of the time. Even where there are errors, you might not notice the effect on the picture or audio, but a computer could notice it. If the errors are bad enough, you will start to get dropouts or distortion. A disc that was burned well and played well might be able to take a lot of damage and still play well - but it will be much closer to the point of not being able to survive much more.

Light is another issue. Burnable media doesn’t like light much. If the light contains a lot of UV rays, the dyes in the media will fade. (Recall how posters and photographs that are in the sun for even short periods every day will lose colour.) If you want a good test of this, burn two identical discs on the same media. Leave one in bright sunshine for a few days (dye side - i.e. the bottom - facing up). I wouldn’t be surprised if even a few days of such exposure caused errors.

Nobody really knows how long burned media will last. Cheap media may only last a few weeks or months. Really good media will last several years if stored well. Some manufacturers claim a hundred years of life, but these tests were done artificially (obviously) and we really don’t know if the claims are accurate. I would expect that a ten-year life is pretty optimistic for all but the best media, and one should err on the conservative side for all but the least important data.

There are ways around this - multiple copies in multiple locations on different brands and batches of media burned on different burners, and reburned at reasonable intervals - but they require some work.


#19

Very good input, [B]PhotoJim[/B], I’ll just comment on this:

That’s not a clear cut. In accelerated aging tests, as an example, TYG02 media doesn’t do well, though “cheaper” discs like CMC MAG E01 are extremely stable and resistant to heat. Not that this contradicts your general statement, just that disc stability is not necessarily a question of [I]price[/I]. :wink:

In the area of stability, among the most “reputable” stuff, Verbatim/MCC seem to do better, overall, than TY. Not that it should have a huge impact on real-world lifespan at normal room temps and humidity levels, but for people living in areas with constant high temps or humidity levels, this could make a difference. :slight_smile:


#20

I’m pretty sure the actual data is pressed into the polycarbonate. To my knowledge, the aluminum layer serves only as a reflective layer, just like recordable media.