Glitch Disc faq
 

This thread is supposed to be used for information about common problems, resolutions and tools to help identify them. If you have something you think needs to be added feel free to post.

I'll allow discussion temporarily for subjects if you feel information is inaccurate or needs to be fixed, but will consolidate that into an official post on the subject. The discussion about it will then be cleaned out so that the faq remains as factual a piece of information as possible.

Layer separation and disc defects
 

Sometimes dual layer DVDs can suffer what's known by terms such as layer separation, delamination, laser rot and DVD rot. These are all the same thing really. What happens is that the glue holding the layers together can come undone. The result is that air enters the cavity between the layers, oxidizing the metal holding the information, destroying it. The reason this happens in the first place is usually as a result of poor manufacturing, but putting extra stress on the hub of a DVD can accelerate this process.

Sometimes when discs are being pressed small flaws and errors are introduced, which can lead to a disc becoming partially unreadable. Depending on the player and the severity the problems will vary from minor glitches to a disc being totally unplayable.

Both disc defects and layer separation are usually replaced free of cost by the studio. To help identify that that's the real issue however it's recommended to use software such as Nero CD-DVD Speed to check it first. Do the following:

- start a software DVD player such as PowerDVD and insert the disc you want to test
- press play once so the disc starts, and then stop it. This is to unlock the disc so that CD/DVD Speed can read the encrypted information
- start CD-DVD Speed
- click the Scandisc tab
- click start
- wait until all of the disc has been checked

On a normal disc you shouldn't get any damaged or unreadable areas. Scratches and physical damage can also make the disc unreadable, but will of course not be replaced by the studio. Some discs that use copy protection however will trigger read errors regardless, and in those cases it's hard to tell whether that's really the problem or not. Post the results in the forum and hopefully we'll be able to figure out if that really is the case or not.

One final note of caution - this will only show whether the disc is having readability issues on your specific dvd drive. What that means is that if your drive is going bad disc errors might be an indication of that instead. Try multiple discs in that case.

Cleaning and repairing discs
 

Cleaning a DVD should be done with a soft lint-free cloth. Wipe radially away from the hub, don't follow the curve of the disc. For particularly hard to remove dirt you can use lukewarm water and dish soap, but make sure the disc has dried properly before inserting it in the player. Normally this won't cause a problem, but in the case of a disc suffering from layer separation this can actually destroy what's left of the disc. Try a cloth first.

Scratches can be repaired using products such as disc doctor which actually grinds down and polishes the scratch to a point where the data is readable again. A rather well known trick is to use toothpaste to grind out the scratch:

- apply a small amount of toothpaste to your fingertip
- rub the toothpaste radially over the scratch until it's ground down
- remove the toothpaste using tissue paper (you might also have to use soap and water, see above)
- test the disc, and if it doesn't work try it again

Cleaning players
 

Over time dust can build up in players and make it hard to read discs. While cleaning discs are sold, they're not really recommended. The brush used can actually damage the laser lens in the worst case, and in the best case it only moves the dust around inside the player, which can lead to other issues later.

The proper way of cleaning a DVD player is to open it up and use a can of compressed air. Only do this if your player is out of warranty as this technically will void it. When opening the player be careful as there may be ribbon cables and other wires that can be damaged if you move too quickly or roughly. "Minimal force" is the key word here. Use the can of air to blow the dust out of the case. Make sure you don't tilt the can too much or you'll get liquid coming out instead, which holds a temperature of -40 degrees. While not harmful in and of itself it's a good idea to let the player sit for a half hour or so to avoid any damage.

Common video problems
 

The MichaelDVD page has a list of some common video problems along with pictures illustrating them. Some of these are correctable by the studio, but the majority of them are in the masters received from the Japanese companies.

Re: Layer separation and disc defects
 

[ QUOTE ]
Skywise said:
To help identify that that's the real issue however it's recommended to use software such as Nero CD-DVD Speed to check it first. Do the following:

- download Nero Infotool and run it to make sure your drive supports C2 error checking. If it doesn't, this procedure won't work unfortunately and you'll have to try using a different drive that does.

[/ QUOTE ]

I thought that C1/C2 errors are for CDs, and PIE/PIF errors are for DVDs. Can somebody confirm this?

I believe that any drive supports the Disc Scan test. Even my CD-ROM drive works with this test. It's the Disc Quality test which has this restriction. Contrary to what I have read that only DVD burners support the Disc Quality test, I have found that my Lite-On 167T is also supported by this test too. If your drive is not supported for this test, you will receive an error when you try to run the test.

The Disc Scan test checks the readability of the disc sectors giving basically yes/no results (or it needed retries). The Disc Quality test gives more detailed information which can be very useful by telling you how many errors there are, and displays this in two graphs. The bottom graph is the most meaningful. As I understand, errors staying in the green (up to 4) are OK, and as they get larger they should be of more concern. Also note that there are what looks like false spikes sometimes that usually are harmless (you can rerun the test on those areas if desired). Wider spikes outside of the green area are also of more concern. I have found that some DVDs cannot be run at higher testing speeds (single layer discs can run especially fast), and give a lot of errors making them look bad towards the end. But you can then select a lower speed from this test (8X) and the disc will then test fine.

These two tests are also very handy for general testing when you receive a new DVD to make sure it can be read OK.

Re: Layer separation and disc defects
 

I'm not completely sure on the C2 bit as my drive supports it. If anyone can confirm either way I'd appreciate it.

Re: Layer separation and disc defects
 

OK, I feel dumb right now. I apologise Skywise for providing some misleading information.

Yes, C1/C2 errors are for CD and PI/PIF/POF are for DVDs. It is an analogous relationship and they conceptually boil down to the same things:

C1 -> PI/PIF (PIF is actually just a large concentration of PI errors)
C2 -> POF

Internally I think of C2 as the same as POF (parity outer failure) and in my head I use the terms interchangeably.

All CDs will have some C1 errors, and all DVDs will have some PI/PIF errors. They are soft errors corrected within the drive and it is always normal to have some. In most cases, only C2 and POF indicate physical problems.

As to the C2 error reporting item in Nero Infotool, that actually has me a little confused: Infotool reports that my Pioneer 106S supports reporting C2 errors, but in reality it can only report POF for DVD media but cannot report C2 for CD media. This makes me suspect that for DVD drives, the C2 field actually reports whether or not it is POF-capable.

It is true that not all error types are reportable by all drives. To my knowledge only Lite-on DVDRw drives and Plextor DVDRw PX-712A and above will report all types. Though some argue that it is misleading for a DVD reader to report C1 or C2 errors on CDs because DVD drives can read CDs much more 'finely' than they were designed to be read.

Re: Layer separation and disc defects
 

Do you guys know of any software that gives accurate information about what's needed to do a proper test? Or is that even needed - are there drives where scandisc either won't work or will give inaccurate results? If it's inaccurate is it a problem of false-positives, false-negatives or both?

Re: Layer separation and disc defects
 

This is where it gets tricky: Doing a "proper test" is harder than you might think: Error correction capabilities vary significantly from drive to drive. What one drive reports as unreadable or marginably readable may be perfectly readable in the next drive. Most importantly, the results of all C2/PIF error reporting methods are functions of both the disc and the drive. They report areas where that specific drive had problems reading the data. You can see a lot of varibility between drives in C1/PI/PIF error levels, though C2/POF tend to be less variable.

Therefore it is not possible to get a truly objective report of the disc's readability using consumer DVD-ROM or DVDRw drives.

If the CD/DVD scandisc function can't operate, it will give the user an error message. But the File Test option will always operate, assuming the disc is unlocked, and this is guaranteed find any data that that specific drive can't read. This could lead to false negatives if the drive had particularly good error correction. Aside from the 'unlocking' issue, the only false positives on DVDs I've seen were fixed through cleaning the disc, though I have seen them on CD-R discs on the last sector of an open multisession disc.

At worst, the File Test will give the user the name of a VOB file that might be bad. They can play to find any area with glitches. If problems are found and are replicable on multiple playback devices, IMO it is a real error. If not, then it could be some drive-specific issue, or the disc is of marginal quality.

"True" disc analyzers that take more "objective" measurements like BLER (block error rate) are traditionally found only in professional laboratories, though the Clover Systems DVX looks promising and relatively inexpensive. It is on my wish-list of things to purchase.