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CD to CD copy quality?

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Sunbuster
Registered User

Joined: 05 May 2003
Location: Finland

Posted: Wed Dec 01 2004 18:55
let me just lay out a theory here: When copying a CD it's not always the case that the data gets copied bit-by-bit as it is on the original. Reason: CD's tend to get scratched. Solution from the CD-drives side: Using the CIRC-decoder to correct small and medium defects (up to 16000 bits), and finally muting the output in case of large defects. The CIRC-decoder hides small defects by recalculating the defect value using the syndromdecoder (which resides inside the CIRC-decoder). Medium defects are hidden using interpolation. So, by this reasoning, unless the CD you're copying is in mint condition, chances are you wont't get a perfect copy, theoretically. Of course, if you listen to the copied CD you probably won't hear a difference because bit errors that can be corrected by the CIRC-decoder are so small they're inaudible. Larger errors of course are audible, because the output gets muted. But in that case you probably won't be able to copy the CD anyway. (LogicDeLuxe explained this already, but I just wanted to add some techical jargon to it ) Another thing of interest might be that the biggest copy-protection schemes out there atm. (Macrovision's Cactus data shield & Sony DADC's Key2Audio) actually work by introducing deliberate errors on the CD to be protected. The errors are small enough for a regular audio-CD player to correct using the CIRC-decoder, but most (especially older) CD-ROM drives aren't able to do the same. for an interesting read on copy protection: http://www.cs.princeton.edu/~jhalderm/papers/drm2002.pdf I been in a mastering studio a couple of times when they've been burning a new master, and during that process they're very strict on people not running around the CD-burner. Reason: outside vibrations might offset the laser and even the tiniest offset means a non-perfect copy will get burnt. Something to think of when burning I guess. Second thing. They never burn above 4x writing speed. Reason 1: higher speeds means increased risk for vibrations and also means should a vibration from the outside occur the damage will be larger as the laser moves a longer distance than with slower burnspeeds. Reason 2: buffer underruns, as LogicDeLuxe said, are not nice. Therefore, burning at a slower speed means the various signal paths don't have to push as much data to the burner. Nowadays this might be more of a theoretical problem, but when it comes to burning CD-masters, the buffer underrun protection that most burners have these days is no guarantee. I guess 4x was a reasonable compromise for their system... EDIT: I btw. second LogicDeLuxe's choice on using EAC for your copying purposes. Good program, able to read stuff when most other proggies already have started complaining.

Inge
Man-At-Arms

Joined: 04 May 2003
Location: Nieuw Lekkerland @ Holland

Posted: Wed Dec 01 2004 20:30

Very interesting read there, young padawan. One thing though:

Quote:

Second thing. They never burn above 4x writing speed.
Reason 1: higher speeds means increased risk for vibrations and also means should a vibration from the outside occur the damage will be larger as the laser moves a longer distance than with slower burnspeeds.

I thought this problem did only occur when cd burners just hit the market (say: six years ago)? I remember people saying (whether that to be some sort of digital urban legend or not) that high burning speeds would result in 'circles' that were just burnt would get damaged by the next 'circle' being burnt. Is that a complete other thing, and was that really an urban legend?

I'll try this EAC somewhere this week. If it does the basic stuff Nero does, but with a proof of quality, then it should be one of my best friends in no time Smile

Inge

Care for a game of Monopoly?

Sunbuster
Registered User

Joined: 05 May 2003
Location: Finland

Posted: Wed Dec 01 2004 22:23
I think it could be perfectly valid that vibrations during burning will cause a slight defect in the burn, since the laser head is in fact on a moving tray and thus can be moved by outside force also. In todays burners though I doubt the error would be so big it would destroy the neighbouring tracks. I'd see it more like a dent in the current track, which could cause the need for CIRC error correction during playback. The reason they're so picky about it in the mastering studio is of course because they want the best possible quality to go to the pressing plant, so they know the customers can't blaim them if something is technically wrong with the production copies. This also means preventing all possible disturbances during burning, even if the're somewhat theoretical these days. About the urban myth thing I don't know... I think there might be some thruth to it since early burners probably didn't have as good a tracking device(motor, laser suspension system etc.) compared to modern burners

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