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Why can't my Plextor copy SD v2.51.021+ perfect? - 8/11/2002 2:04:06 AM   
Clint


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First off, you need to fully comprehend exactly what EFM (Eight to Fourteen Modulation) encoding is:

    Eight to Fourteen Modulation is used during encoding, because the 8-bit 'magnetic' byte has to be modulated to a 14-bit 'optical' byte. Technically, this modulation is necessary to allow encoding of two consecutive 1s--which would be impossible with the scheme of pits and lands using 8-bit bytes (1s and 0s). In fact, the changes in reflectivity (as the laser light moves along the sequence of pits and lands) are coded as 1 channel bits. Two consecutive 1s are therefore not possible. Moreover, the 'lands' in between the 1s are represented by 0 channel bits, and the number of 0s represent the run-length. The bits in an optical byte are known as 'channel bits' to avoid confusion, and because they are transferred to the controller board through a specific channel. Furthermore, the fourteen-bit optical byte is provided three additional channel bits, known as merging bits--to eliminate transition conflicts between consecutive optical bytes. During the read process, the interface card demodulates the 14- bit optical code to the 8-bit code used by the computer--and all channel bit-level modulation and processing remain transparent to the user.

Now with that in mind, this is how SD2 works:
A regular bit pattern (such as XYXYXYXYXYXY...) fed into the EFM encoder can cause large values of the Digital Sum Value in case the merging bits cannot reduce this value. The scrambler (something found in every CD-ROM/CD-RW) reduces this risk by converting the bits in byte 12 to 2351 of a Sector in a prediscribed way. The sectors mentioned above try in fact to overload the EFM encoder of the CD-Writer, because *AFTER* passing the scrambler the poor device has to write *REGULAR BIT PATTERNS* - something it really doesn't like. Thats how SD2 works. [Plextor recorders *CANNOT* write SD2.51 correctly due to additional weak sectors added by MacroVision, whereas SD2 *PRE* v2.51.021 the Plex 24X & and 40X could cope with those weak sectors.]

Technically, this is why Plextor's (and many other "recognised" SD2 < v2.51.021 killers) fail in producing a backup that is readable in *every* drive.

However, CloneCD's Ampliy Weak Sectors (and other programs) have introduced sector amplification techniques, that try (and most times do) overcome the havic that weak sectors (and regular bit patterns) cause to EFM encoders in CD-RW drives.
Sometimes AWS setting can produce wokable backups that play eveywhere (in some recorders) --> this cannot be warrented.

Drives capable of writing regular bit patterns correctly are on the increase, most drives supporting this feature are based apon MediaTeK chipsets, although, there are other chipset manufacturers out there that also support this *important* feature.

Fingers crossed that the upcoming PLEXTOR PleXWriter 48/24/48A (PX-W4824A) will support this! [^]

I hope that you finally understand the importance of a device to write "correct EFM encoding of regular bit patterns" when copying a SD2 protected CD.






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    RE: Why can't my Plextor copy SD v2.51.021+ perfect? - 8/12/2002 3:17:47 PM   
    SirDavidGuy

     

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    I normally wouldn't have replied, but I just couldn't stand all the left out information.

    On AWS:

    AWS "weakens" the sectors by patching certain bytes in it that reduce the DSV drastically, but it leaves the ECC/EDC intact. The modifications are corrected On-The-Fly by the reader. SafeDisc 2's guard module cannot check if this is the case, because not all readers support the DCR bit being set to 1 in the READ CD command. AWS is in no means a 1:1 copy, in case anyone was still wondering.

    On weak sectors:

    The DSV is an integer determined by the number of pits and lands (meaning it can only be calculated after NRZI encoding). Every pit increments the DSV, and every land decrements it. The only people who really know why the DSV must be kept low work in drive manufacturing plants, but the most viable (non-professional) theory is that since the drive receives none of the light reflected by pits, that it will have to lower the threshold for the crossings of the beta values, possibly returning incorrect information later on in the read.

    quote:
    The sectors mentioned above try in fact to overload the EFM encoder of the CD-Writer


    The EFM encoder doesn't get overloaded. It is just a simple lookup table. The problem lies elsewhere.

    The Scrambler:

    Is a shift register used to "randomize" the data. The SafeDisc 2 Sectors are pre-scrambled. Due to the nature of the XOR operation, when it is scrambled again for writing, it is reverted back to the original (unscrambled) pattern.


    (in reply to Clint)
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    RE: Why can't my Plextor copy SD v2.51.021+ perfect? - 8/13/2002 2:27:53 AM   
    Clint


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    Thanks SirDavidGuy for the 'extra' info.

    The topic was titled *perfect* backup, and as such, all the info you have provided on AWS was unnecisary for the topic, but usefull none the less... It was written for people wondering why their Plextor's (and others) couldn't perfectly backup newer SD revisions *without AWS*. And as we all know/should know, AWS is not perfect as it changes the data ("weak" sectors), and modifies these in a way that all CD readers can revert it back, so it is recognised as the original...

    quote:

    The EFM encoder doesn't get overloaded. It is just a simple lookup table. The problem lies elsewhere.




    I seem to disagree, the weird thing is that if a SD2 copy doesn't play in a CD-ROM, this copy has additional bad sectors, which weren't on the original. As CloneCD reads and writes "as is!", one would have assumed, this is simply impossible.
    If you want to find the answer, you can look at these sectors on the original disc (where they are readable).
    You will find a lot of jibberish on the first view. But if you run these sectors through a sector scrambler (a device, which is in every CD-ROM and CD-WRITER) you see the reason for all the trouble: Regular patterns like 'XYXYXYXYXY...' and so forth.

    And this is exactly how the protection works. To understand this, you need to know, what the scrambler is used for (from ECMA-130, ISO/IEC 10149):

    "A regular bit pattern fed into the EFM encoder can cause large values of the digital sum value in case the merging bits cannot reduce this value. The scrambler reduces this risk by converting the bits in byte 12 to 2351 of a Sector in a prediscribed way. ..."

    quote:

    Oliver Kastl:
    The sectors I have mentioned above (1st post) try in fact to overload the EFM encoder of the CD-Writer, because *AFTER* passing the scrambler the poor device has to write *REGULAR BIT PATTERNS* - something it really doesn't like.





    Olli himself states that it does in fact try overload the EFM encoder, you say different problem...

    Who to believe






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    Edited by - Clint on 08/13/2002 02:36:34

    (in reply to Clint)
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    RE: Why can't my Plextor copy SD v2.51.021+ perfect? - 8/13/2002 10:29:24 AM   
    SirDavidGuy

     

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    quote:
    If you want to find the answer, you can look at these sectors on the original disc (where they are readable).
    You will find a lot of jibberish on the first view. But if you run these sectors through a sector scrambler (a device, which is in every CD-ROM and CD-WRITER)


    Yes, of course.

    I've even scrambled them myself.
    (One of the scrambled patterns is: D9 04 D9 04, which goes into the EFM code [with merging bits] as 10000000010001 000 01000100000000 100 10000000010001 000 01000100000000. Try checking the DSV on this, it's quite large!).

    quote:
    Olli himself states that it does in fact try overload the EFM encoder, you say different problem...

    That's not what he meant (unless he's mistaken, which is entirely possible). The EFM proccess cannot go wrong, barring some unforseen circumstance such as it being corrupted, or having bits flipped by a magnet, etc.). It is just a lookup table.

    I have it on the source of one who designs CD-Burners that the EFM encoding process will not go wrong.

    CD Freaks Mod

    (in reply to Clint)
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    RE: Why can't my Plextor copy SD v2.51.021+ perfect? - 8/14/2002 12:06:02 AM   
    Clint


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    You could be right, maybe he did make a mistake!??

    It would be nice if he could drop by and tell us what exactly he meant by that.

    The source of his statement "those sectors in fact try to overload the EFM encoder" is from www.cdmediaworld.com

    Yeah the DSV is very large, unbelievable even!

    Again, thanks for expressing your point of view on the subject and for the info .

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    (in reply to Clint)
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    RE: Why can't my Plextor copy SD v2.51.021+ perfect? - 8/14/2002 9:25:22 AM   
    SirDavidGuy

     

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    quote:
    You could be right, maybe he did make a mistake!??

    It would be nice if he could drop by and tell us what exactly he meant by that.


    My guess is that he used it for the lack of a better term (eg. Well, when the EFM encoder outputs sectors with a high DSV, it gets all messed up somewhere and it doesn't work).

    With any luck, I will have found the real problem writing weak sectors soon.

    CD Freaks Mod

    (in reply to Clint)
    Post #: 6
    RE: Why can't my Plextor copy SD v2.51.021+ perfect? - 8/15/2002 5:59:12 AM   
    Clint


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    quote:

    when the EFM encoder outputs sectors with a high DSV, it gets all messed up somewhere and it doesn't work






    Yeah, but where is the big puzzle?!

    Anyone (Olli) want to get to the bottom of this

    Anyway, now to get back to testing...

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    Edited by - Clint on 08/15/2002 06:01:01

    (in reply to Clint)
    Post #: 7
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