Amazed: DVD polish worked!

[pamela]

Don't data CDs have additional redundant data to help handle that sort of error?

[tabbypurr]

There was also a demo of cds being towed on string behind a vehicle then played. IIRC all the ones that were still in 1 piece still played - it must have been a fake.

NT

[Adam Funk]

Didn't one of the CD copy-prevention schemes consist of deliberately adding errors that an audio player could burp through but a pickier CD drive would have trouble with?

[whisky-dave]

wasn;t there a derek and clive sketch about that (braso and rubing) something like dickie back riding.

My dad useedd the 'liquid' from the corner of his eye to polish and remove sctraches on negatives back in the early 50s and 60s. People at my camera club still used this method until the 80s at least.

[Andrew Gabriel]

Don't know about CD's, but something like that was certainly used on floppy disks. Certain sectors were destroyed, and the software on the disk checked that those sectors were unusable, and failed to run if copied to another disk where that wasn't the case. (That copy protection scheme was broken quite quickly too.)

[Vir Campestris]

Yes.

An audio drive will just keep playing, and try to correct - and the errors were designed to be correctable. A data drive will first try to read it correctly, then try again, then (oops the music has stopped)

Andy

[Johnny B Good]

But before it got to the "Oops, the music stops" point in the case of an audio CD player, the 'error correction' would resort to 'faking it' once it couldn't 'losslessly' correct the errors by repeating the previous few millisecond's worth of the track (I don't recall what the exact number of milliseconds was deemed to be 'beyond the pale for this final attempt to 'paper over' the problem).

What this means is that the playback fidelity was not necessarily guaranteed to be 100% perfect under such marginal cases of damage or surface contamination. The only certain way to guarantee perfection would be to rip the audio tracks to a music or iso file and verify that the ripping software had no errors to report in its logs.

[Adam Funk]

I've got a vague recollection that some copy-protected CDs weren't actually labelled with the official CD logo/trademark because although they played in audio CD players, they didn't actually comply with the official standards for CDs.

[Brian Gaff]

Well, dvds I think are different. the problem seems to be loss of where the heck it is, not loss of just some bits of data.

Inote that some cds will copy fast whiile others keep stepping down the speed till it works on some software. as this can be different on two cds from the same collection I doubt the issue is protection, its more likely poor production ie warped or faulty media in the first place.

Some players are more tolerent, notably the cheap tesco bookm boxes work better than an expensive marantz. Crazy. Brian

[Vir Campestris]

No.

The audio drive would read the sector, then run the error correction on it. Unless the disc was filthy or scratched then the error correction would successfully "correct" the "errors" to the correct music, and would play it perfectly.

A data drive would always do a reread before attempting the correction.

The built-in "errors" reduce the headroom for error correction. If your disc is moderately badly scratched then it could result in a disc where the player would fake missing data by repeating a short bit as you describe above. If it isn't scratched, it plays fine. If it's badly scratched then it won't play - but nor would a normal disc. It's only the in-between stuff where there are problems.

That was the second session stuff that confused some PCs into not playing them at all - seeing only the second (data) session, not the audio.

Of course, if you are Sony then you ship a rootkit on the second session which is autoinstalled without any consent from, or notification to, the user when the disc is installed in a PC, and you leave vulnerabilities in the rootkit such that they can be exploited by any subsequent malware writer.

And thus destroy the entire CD copy protection industry.

Andy

[Adam Funk]

Destroying the CD copy protection industry was a good thing. Now if we could just destroy the locks on DVDs that force you to watch crap before you can start where you want....

[Vir Campestris]

Use a ripping program. They'll walk straight past that stuff.

Thus of course converting you from a law abiding customer into an evil villain... ;)

Andy

[whisky-dave]

Yeah and on the copied ones I;ve seen I don;t have to view that crap only the people that pay for their DVD have to watch it which seems rather unfair. But the music and film industry couldn't care less if they tried.

[Adam Funk]

I know, I should put together a home media server thingy. But I replaced our DVD player last year with (another) region-unlocked one, & it irritates me that you can't buy one that's also "operation-not-permitted"-unlocked.