An informational white paper by Robert
DeMoulin © 2004 Sony Electronics Inc.
Dual Layer Burning and Recording – The Basics
While consumers around the world have enjoyed
burning their own DVDs for a few years now, the inevitable question of
“what’s next” is now upon the industry. Certainly blue laser
technologies such as Blu-Ray will one day become affordable and
prevalent; however consumers today are still very much in love with
DVD. The DVD format is mature, high quality content is widely
available, and players are low cost and now installed in approximately
53 percent of U.S. households.
Dual layer DVD technology is not new. Commonly
called “DVD9,” Hollywood has been churning out major motion pictures
on stamped dual layer DVD Discs for years. How else could they include
the full length movie plus all the bonus materials commonly found on
today’s DVDs? Because dual layer technology has always been part of
the DVD specifications, dual layer DVD Recording on the desktop is the
natural progression of single layer 4.7GB recordable technology.
Dual layer DVD recordable discs offer up to
four hours of high quality MPEG-2 video, or up to 8.5GB of data on a
single sided disc with two individual recordable “layers”. Dual layer
capable recorders will have the ability to record on the new dual
layer DVD recordable discs as well as traditional single layer DVD
discs and CDs too. Want more? Because a recorded dual layer DVD disc
is compliant to the DVD9 specification, the discs are compatible with
most consumer DVD players and computer DVD-ROM drives already
installed in the market.
How Are Dual Layer Discs Recorded?
Single-sided dual layer recordable discs are
constructed by one dummy polycarbonate platter base and the other one
that contains a single organic recording layer. Dual layer recordable
discs contain two organic dye recording layers (termed L0 and L1,
respectively) between dual polycarbonate bases and semi-reflective
metal layers separated by a transparent spacing layer. Single layer
DVDs have a wobbled pre-groove molded into the polycarbonate base that
control the rotation speed of the disc and provide the addressing
scheme for the disc. In a dual layer recordable DVD, each recording
layer has its own wobbled pre-groove that controls rotation speed and
addressing for that layer. However, the entire “table of contents” and
system area of a dual layer recordable disc is contained only on the
first recordable layer (L0).
When a dual layer recordable disc is inserted into
a dual layer compliant recorder, the optics will focus the laser at
one of the dual layers to try and detect an “Address In Pregroove” (ADIP)
signal. From the ADIP signal, the recorder can detect whether the disc
is dual layer and which layer it’s focused on. Once the media type and
the layer are detected the laser will be able to move down or up its
range of focus to access any one of the two recordable layers. The
drive will then focus on the Lead-In area of the disc to determine
whether the disc is completely blank, partially recorded in
Multi-session format, or Finalized (completed).
The two layers represent one contiguous address
stream for recording as a Video Disc, a DVD-ROM, or even a packet
recorded disc. When recording on dual layer media, the drive first
records on the first recordable layer L0 from the inside hub area
outward, just like a typical DVD recordable disc. When the end of
information recorded in L0 is reached, Middle Zone 0 is added. Next,
the drive focuses on the second recordable layer L1 to create Middle
Zone 1 that over-wraps Middle Zone 0. The disc is then recorded
from the outside rim inwards. Multi-session discs can be recorded with
dual layer recordable media, so it’s possible to add data in
“sessions” on a disc.
First Layer Recorded Inside Hub To Outer Disc
Second Layer Recorded Outside Rim Towards Disc
Reflectivity of both recording layers of a dual
layer recordable disc is the similar: greater than 18 percent. The
reflectivity between the L0 and L1 layers however, is greater than 50
percent because the upper (second) recording layer absorbs and
reflects some of energy that is directed at the lower (first)
recording layer L0, in order for organic dye to be recorded. As a
result, the organic dye formulation and shape of the pre-groove in
dual layer discs must be optimized to provide the appropriate
reflectivity for both layers. The spacer layer separates the two
recording layers and prevents cross layer recording. It is transparent
to allow the laser to easily focus on either recording layer by simply
changing the position of the laser’s object lens.
The Recordable DVD Format Debate and Dual
Both the DVD Plus (“+”) and Dash (“-“) formats are
still very much alive and well and appear to be with us for the
foreseeable future. Presently, the DVD+RW Alliance is the first of the
two organizations to present a Dual Layer recordable standard. The
formal name of the format is Double Layer. Initially available only in
a write once format called DVD+R DL, this technology should debut by
the middle of 2004 with drives and media from several major
manufacturers including Sony. Recording speeds for DVD+R DL are
initially 2.4X, however they are expected to increase in the future.
Drives supporting DVD+R DL will also be able to record single layer
discs at up to 8X or faster (using write once media) and support
high speed CD-R/RW burning as well.
What of the DVD Forum and the Dash format? While
not available at the time of this writing, its expected that the DVD
forum will offer up a recordable dual layer disc specification in the
near future and probably within 2004.
Certainly dual format DVD burners are overtaking
the commercial market and Sony was the Pioneer of Dual Format burners.
Sony is a member of, and is committed to continuing to support the
DVD+RW Alliance and the DVD Forum for dual layer DVD
Applications For Double Layer Recordable
to four hours of high quality MPEG-2 video on a single sided disc,
consumers can really take their home movies to the next level with
dual layer DVD recording. One benefit of the additional space is the
ability to increase the bit rate of the video when authoring to get
higher quality on the finished disc. Typical DVD authoring software
applications use variable bit rate encoding to maximize utilization of
the DVD disc space. By forcing the application to always encode at the
highest bit rate supported, more space will be used on the disc,
however the quality difference is noticeable and worth it.
Dual layer DVD recording makes it possible for a
consumer to create longer home movies and even consolidated many home
movie projects onto a single disc. Let’s not forget that up to 8.5GB
of uncompressed DVD disc space is a great place to store data and keep
your PC’s valuable data, applications, and settings backed up for when
disaster strikes. You can pack up to 12 CDs or 5,902 floppy disks’
worth of information onto a single dual layer DVD disc.
With the additional capacity of a dual layer DVD
recordable disc, a consumer can store approximately 2,000 songs in MP3
format or up to 17,000 high quality JPEG images. Talk about a cool
place to store all that stuff cluttering up your hard drive!
(left) and DRX-700UL (right) Double Layer Dual Format Drives
businesses that have already embraced DVD for the distribution of
training video on DVD know that more space is often needed to deploy
all of the material. Just like with the example provided for consumer
applications, higher bit rate encoding of the video translates into
better quality training video for the viewer. Some of the world’s best
companies, from major automobile manufacturers, fast food restaurant
chains, and others, depend on DVD for their training video needs for
one simple reason – it works.
Independent filmmakers and studios alike will
appreciate the ability to author a dual layer DVD video disc and try
it out without resorting to expensive and time consuming replication.
This group of users can now fine tune their works on cost effective
dual layer DVD recordable discs before creating the master for
Certainly business users will appreciate the
increased storage capacity of a dual layer DVD recordable disc when
distributing a large amount of data on a single disc is needed, and
even for desktop system backup and single server backup with time and
cost savings over traditional tape technologies. IT managers can even
create their system “images” for configuring client PCs on a single
disc for rapid deployment of new computers on corporate networks.
Dual Layer Implications For DVD Recording
Because double layer recordable discs are
basically one contiguous stream of block addresses, it’s not very
difficult for software makers to make their disc mastering software
compatible with dual layer drives and media, as least where
recording data is concerned.
DVD Video authoring software has to manage the
“break point” of where the video will be split between layers. This
“layer jump” is typically not visible when you watch a DVD movie even
though there is a very brief interruption to allow the player to focus
on the second layer. Managing this break point is difficult but
straightforward once all the video for a project has been imported
into the authoring application where it is separated and allocated for
a video DVD.