Re: How common are small surface defects on blank DVD-R media?

Discussion in 'DVD Video' started by Will Dumes, Jul 27, 2003.

  1. Will Dumes

    Will Dumes Guest

    ies (Walt) wrote:

    > Is it normal for blank DVD-R media to have occasional specks of
    > dirt underneath or blemishes on the surface which cannot be
    > removed? I see at least a couple tiny flaws on every few discs.
    > In one spindle, nearly half of my discs had a small circular
    > scratch that went most of the way around the disc.
    >
    > Each time I used these imperfect discs they worked fine (based
    > on file compares before and after), but given how small the data
    > is on a DVD-R compared to a CD-R I'm worried that maybe I should
    > not use media with imperfections on the surface. I don't know if
    > the reason these discs work is because the error correction is
    > so good or the laser is still able to burn the dye through small
    > surface defects. Anyone know?
    >
    > Can others tell me if they commonly see these type of surface
    > flaws and still use the media? Am I worrying about nothing and
    > should I consider these discs as reliable as media with perfect
    > surfaces, or should I avoid using any imperfect media?


    Did you post this in another group recently because I answered a
    similar question.

    For pure data there is a lot of redundancy for error checking. This
    happens at bit and byte levels (as far as those terms for binary data
    apply). A few minor scratches will probably have zero effect,
    especially if they are radial rather than arcs.

    For analogue material like audio there is little redundancy but the
    effect is far less likely to be noticed.

    For burning, the issue is slightly more sensitive. If you are very
    concerned then do a comparison of the burnt DVD-R with the source
    material. Personally I fin dit not worth the chore but you might
    want to do it.
    Will Dumes, Jul 27, 2003
    #1
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  2. Will Dumes

    Walt Guest

    On Sun, 27 Jul 2003 19:38:17 +0100, Will Dumes
    <> wrote:
    >Did you post this in another group recently because I answered a
    >similar question.


    Yes, that might have been my first post, and I saw your reply (thanks
    for posting it). However, I shortened and changed the focus of the
    questions and then reposted hoping for more than just your 1 response
    because I'm trying to find out how common these defects are on blank
    DVD-R media. Maybe I should have titled the post "Poll: how many
    people burn DVD-R media with imperfect surfaces?"

    You answered that there is substantial error correction for data which
    may explain why I see no errors on imperfect media when I compare
    files before and after, assuming that "DVD Video" qualifies as "data".

    What I'd like to know next is if most people see little minor problems
    on their media and they use it anyway successfully, or if people
    typically avoid burning any media with any surface flaws.

    Does the laser still penetrate through a scratch or "inclusion" inside
    the surface, or does it defract and not burn the dye meaning we are
    always relying on the error correction? What about a circular scratch?
    If it is lined up with the track (a "prewobbled groove" I think I once
    heard it called) then it seems it could potentially affect enough
    subsequent data to overcome the error correction. However, I doubt any
    scratch would line up just right.

    >For pure data there is a lot of redundancy for error checking. This
    >happens at bit and byte levels (as far as those terms for binary data
    >apply). A few minor scratches will probably have zero effect,
    >especially if they are radial rather than arcs.


    Is "DVD Video" as burned by Nero considered pure data with a lot of
    error checking?

    >For burning, the issue is slightly more sensitive. If you are very
    >concerned then do a comparison of the burnt DVD-R with the source
    >material. Personally I fin dit not worth the chore but you might
    >want to do it.


    That's what I do, and so far no errors, but I don't feel confident
    using imperfect discs -- which is why I want to know if other people
    bother to look at the surfaces before burning. If they do, is most
    media perfect and I have just been unlucky or is most media imperfect
    and people just use it anyway? I guess it partly depends on a person's
    vision, how much they care, and whether they use a can of compressed
    air to clean off the surface first.

    From ies (Walt):
    >> Is it normal for blank DVD-R media to have occasional specks of
    >> dirt underneath or blemishes on the surface which cannot be
    >> removed? I see at least a couple tiny flaws on every few discs.
    >> In one spindle, nearly half of my discs had a small circular
    >> scratch that went most of the way around the disc.
    >>
    >> Each time I used these imperfect discs they worked fine (based
    >> on file compares before and after), but given how small the data
    >> is on a DVD-R compared to a CD-R I'm worried that maybe I should
    >> not use media with imperfections on the surface. I don't know if
    >> the reason these discs work is because the error correction is
    >> so good or the laser is still able to burn the dye through small
    >> surface defects. Anyone know?
    >>
    >> Can others tell me if they commonly see these type of surface
    >> flaws and still use the media? Am I worrying about nothing and
    >> should I consider these discs as reliable as media with perfect
    >> surfaces, or should I avoid using any imperfect media?
    Walt, Jul 27, 2003
    #2
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