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Why do layer changes vary in quality?

Discussion in 'Movie Forum' started by plasmattack, Jan 22, 2003.

  1. plasmattack

    plasmattack
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    There's an old thread floating around about particular DVDs that suffer poor layer change. (I'm not talking about the timing of the change within a film but about the less-than-seamless nature of the change.) However, there's no comment on why some changes are worse than others.
     
  2. Lux

    Lux
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    the changes are all the same.
    It's where they are and how your player handles them:
    If a layer change is in the middle of the film u'll see it. and if your player is not too good at handling them you'll notice them even more.
     
  3. plasmattack

    plasmattack
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    There's some comment to the effect that superbit discs have fairly seemless changes.
     
  4. Geezer

    Geezer
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    I havent noticed any difference between superbit layer changes and the norm.
     
  5. Ian J

    Ian J
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    Have you watched a normal film and the superbit version of the same film then.
     
  6. Geezer

    Geezer
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    No i have not. :blush:
     
  7. Squirrel God

    Squirrel God
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    They're not I'm afraid. There are sometimes differences in layer changes from disk to disk (even between two copies of the same DVD). I have noticed this with two copies of Shallow Hal that I had. Admittedly, however, the differences are barely noticeable. I can't see that this would have anything to do with the data on the disk as this would be uniform across all copies, however it could have something to do with the bonding.
    Just to add to this point, some DVD authors are just plain dumb and stick the layer change right in the middle of a scene or in the middle of dialogue (There's Something About Mary R4 is a prime example of the latter!). When layer changes are between scenes, they are much less noticeable and do not interrupt viewing (many would not notice them at all). Many of the recently released DVDs seem to be taking much more care with layer change positioning, which is nice to see at last :)

    Players can vary significantly with how quickly they can change layers, and some of the higher end player (e.g. Denon's), use a buffer so you can't even notice the layer change (not noticeable on a PC either due to the drive caching).
     
  8. Whatts

    Whatts
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    I found the placement of the layer change in the Royal Tennenbaums pretty decent. Royal knocks on the door and then there's the layer change, so you just have a still of the door for a second.
    Very well done, I wish more layer changes were placed like this...

    - Tom -
     
  9. James45

    James45
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    the placement of some modern layer changes are quite clever like that one, at least it shows some people are putting some thought into the production of dvds and trying to minimise the inconvience to the user
     
  10. Squirrel God

    Squirrel God
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    Donnie Darko has two layer changes that are very carefully placed :)
     
  11. Daneel

    Daneel
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    2 layer changes? :confused:
    It is a 3 layer DVD? :eek:
    Never heard of that before.
     
  12. Squirrel God

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    Yeah, tis an odd one. It's the only DVD I've found it on. It's still 2 layers of course, but it appears to switch from one layer to another just for one chapter, then it switches back (hence two changes). I can only think that they did this to prevent a single layer change occuring in a bad place. The disk is certainly packed with extras and there is probably precious space left on the disk, so presumably all the data had to be optimised as much as possible as well.
     
  13. CWB

    CWB
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    There is the notorious layer change on "Bridge on the River Kwai", which involves the counters resetting to zero and the picture freezing or about 2 seconds. This has to be the worst ever.
     
  14. James45

    James45
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    yep and it's in the middle of a pan as well in Jack Hawkins' office, can't remember there being any dialogue at that point tho so I suppose we should count ourselves lucky.
     
  15. Lex

    Lex
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    :D Not only did you have two copies of it, but you watched them both!! You must love that film!! :D
     
  16. EvilMudge

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    There are two formats of DVD with layer changes,

    SS-DL and RS-DL.
    SS-DL is a single side dual layer - basically two normal DVDs stuck together.
    RS-DL is a reverse spiral dual layer, the second layer works outwards instead of inwards, so the player should merely have to refocus and find the start of the layer rather than move the head to the outer edge of the disc again and then change layers.
    How much this affects the speed of the layer change I don't know, as modern players are much faster ie It's painful to watch on my old Pio 525 but almost unnoticeable on my new 350.
     
  17. Squirrel God

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    Yes, that's a good point but just to add, and possibly make a couple of corrections to what you've said.

    RSDL and SSDL are different concepts. SSDL just refers to a DVD-9. RSDL refers to a mastering process that is available for all DVD formats with dual layers (either dual layers on one side, single layer the other side, or dual layers both sides), i.e. DVD-9, DVD-14 and DVD-18.

    All DVDs use a bonding process to stick 2 DVDs together. If the disk is single sided, then the top layer is just a 'dummy disk'.

    Regular mastering is known as PTP (parallel track path). Laser reads the data from the centre to the edge for both layers.

    OTP (opposite track path) is what's commonly known as RSDL. Laser reads the data from the centre to the edge for the first layer, and from the edge to the centre for the second layer. Thus, as you say, speedier layer transitions are possible because there is less physical movement required when changing layers.
     

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