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Appeared on: Monday, March 15, 2004
BD Vs AOD


1. Page 1

HD-DVD (AOD) Vs Blu-Ray (BD) - Page 1

There has been a lot of discussion lately regarding the two most prominent recording formats being promoted for HDTV use. Looking back at the recent past we could say that the same groups that had fought over DVD-Video formats before it was finally standardized, are still fighting for two new formats. On one side of the fence we have two Japanese giants of the consumer electronics industry, NEC and Toshiba. They have jointly developed the "AOD" (Advanced Optical Disc) format for HDTV recording applications. The main argument for AOD is that it is play-compatible with DVD-Video, and so it is often called "HD-DVD" for that reason. Sony and Philips along with Hitachi, Sharp and Samsung stand on the other side. They are promoting the "BD" format, which is better known as the "Blu-Ray Disc". Both formats initiate evolutionary higher capacities than current DVD-Video.

Structurally, HD-DVD is identical to DVD-Video, employing two 0.60mm thick discs that are bonded together to form the HD disc. It can store 15GB on a single layer DVD. HD-DVD recordings can therefore be replicated on the same equipment and manufacturing infrastructure used to replicate standard DVD-Video recordings. As a result, this minimizes disc production costs.

BD Main Specifications

Read-only
Rewritable
Data capacity
Single-layer 15GB/sideDual-layer 30GB/side
Single-layer 20GB/sideDual-layer 40GB/side
File format
UDF
User bit rate
36Mbps
Disc size
120mm (diagonal), 1.2mm (thickness: 0.6mm x 2)
Laser wavelength
405nm
Lens numerical aperture (NA)
0.65
Track structure
--
Land & groove
Signal processing
PRML
Modulation
2/3 conversion

Toshiba and NEC insist that the provided 15GB of capacity is more than adequate for HDTV software applications. The compression algorithms used in HD-DVD are different from those currently in use, so there are claims that the 2/3 conversion could reduce picture quality. On the other hand, the format features the same 0.6 numerical aperture for the object lens and disk structure as the current DVD disk system. The companies stressed the importance of backward compatibility. Taking advantage of this compatibility, NEC has developed a HD DVD drive that employs a single optical head. The head has blue laser and red laser diodes as light sources. However, the lasers share the same object lens. Newly developed ICs handle the physical difference between DVD and HD DVD.

NEC claims the single optical head structure enables production of smaller and thinner HD DVDs at lower cost. Using the single head, NEC developed prototypes of full-and half-height drives that achieved 15 Gbytes for a single-layer ROM disk, 30 Gbytes for a double-layer ROM disk and 20 Gbytes for rewritable disks.


2. Page 2

HD-DVD (AOD) Vs Blu-Ray (BD) - Page 1

Sony and Philips, along with Hitachi, LG, Matsushita, Pioneer Samsung Electronics, Sharp and Thomson Multimedia are promoting the "BD" format, which is better known as the "Blu-Ray Disc".

Blu-Ray main specifications

Read-only
Data capacity
23.3GB/25GB/27GB
User bit rate
36Mbps
Disc diameter
120mm
Disc thickness
1.2mm (optical transmittance protection layer: 0.1mm)
Recording format
Phase change recording
Laser wavelength
405nm (blue-violet laser)
Lens numerical aperture (NA)
0.85
Tracking format
Groove recording
Tracking pitch
0.32um
Addressing Method
Groove recording
Shortest pit length
0.160/0.149/0.138um
Recording phase density
16.8/18.0/19.5Gbit/inch
Video recording format
MPEG2 video
Audio recording format
AC3, MPEG1, Layer2, etc.
Cartridge dimension
Approximately 129 x 131 x 7mm
Video and audio multiplexing format
MPEG2 transport stream
Modulation
1.7PP (Parity preserve/Prohibit RMTR)

By adopting a 405nm blue-violet semiconductor laser, with a 0.85NA field lens and a 0.1mm optical transmittance protection disc layer structure, it can record up to 27GB video data on a single sided 12cm phase change disc. This means that 2 hours of digital high definition video and more than 13 hours of standard TV broadcasting (VHS/standard definition picture quality, 3.8Mbps) can be recorded on a disc.

In addition, the Blu-Ray specification includes the usage of an optical disc cartridge which protects the optical disc's recording and playback phase from dust and fingerprints.

The basic disadvantage of the Blu-Ray format is that it requires a new manufacturing infrastructure resulting in increased expense while implementation could prove a long-term process. In addition, the Blu-ray Disk format lacks backward compatibility with current DVDs.

Sony, a prime supporter of Blu-ray Disc, has already developed Professional Disc. The format is available in two variants and is targeted at the specific markets of high-definition broadcast quality video and data archiving and storage. The BDZ-S77 is currently available in the Japanese market, but there are not any plans for launching the recorder overseas. Several Japanese companies, including Sony, Hitachi Maxell and TDK, already offer blank Blu-Ray disc media. The recorders and media are expensive, but they are obviously first-generation units whose prices will decline rapidly as market acceptance takes hold.

In contrast to the HD-DVD proposal, Blu-Ray rejects the use of a new video compression format, sticking with existing audio/video codecs such as MPEG-2 and Dolby Digital that are specified by the U.S. digital HDTV system. Blu-Ray media makes use of a completely new technology that requires no new advanced compression algorithms, and is totally different from either DVD or HD-DVD (AOD). It will therefore require new facilities for the manufacture of the discs. Blu-Ray also makes use of a highly specialized high numerical aperture (0.85) lens and what is called near-field recording technology, using a single platter 1.1mm thick, with a special 0.1 focusing overlayer on the active side of the disc. Both HD-DVD and Blu-Ray use 405nm blue-violet lasers for writing and reading. All DVD-type products require 650nm red lasers and a conventional focusing system, which are both much cheaper than the 405nm lasers and special near-field high numerical aperture lens systems required for a Blu-Ray recorder or player.

The DVD Forum appears to be considering several codecs as candidates for the HD-DVD. These include H.264, the technical specification of which is scheduled to be decided in March; MPEG-4 Advanced Simple Profile; MPEG-2 with a so-called "enhancement layer;" and Microsoft Corp.'s Windows Media 9. All the codecs have reportedly produced satisfactory high-definition quality pictures at the DVD Forum's technical working group, packing 9 Gbytes of high-definition content onto a two-layer DVD using a red laser, with encoding bit rates as low as 7 Mbits/second.

Some days ago, the rewritable HD-DVD (High Definition and High Density-DVD) format was approved in the DVD Forum's general meeting, held in Tokyo. The new format specifies a 12cm optical disc that can store up to 20Gb of data on a single-sided disc. Toshiba and NEC have jointly developed the format, while a read-only version of HD-DVD was approved late last year.


3. Page 3

HD-DVD (AOD) Vs Blu-Ray (BD) - Page 3

Although the DVD Forum seems to be currently backing HD-DVD, the format with the largest number of backers is Blu-ray Disc, with 12 companies sitting in on the format committee. Blu-Ray was initially targeted at recording of high-definition video. However, the latest addition of Hewlett-Packard and Dell to the format steering committee is expected to result in a widening of its target market to include the computing space. Of course pricing makes such products unreachable for the mid-user.

Plasmon has also launched its own format called UDO (Ultra Density Optical), which is also targeted at the data archiving and storage market as a replacement for MO (Magneto Optical) discs. UDO uses 405nm blue-violet laser and phase change technology adapted from the Blu-Ray DVD-type products. UDO drives operate with an 8KB sector size with direct overwrite capability.

Besides the “violet laser” solutions, the industry has also received proposals based on red lasers. Warner Bros has proposed the HD DVD-9 compression method, applied on regular red laser DVDs. This will allow for the format to launch faster because current facilities can be used and the change in the current way DVD players work are minimal. It supports development of backward compatible players that can playback current and next generation DVD.

The weak part of the HD-DVD-9 format is that it can only store 4,7GB on a single layer DVD. HD content has more than twice the resolution of normal DVD and therefore also fills much more in raw data. However, it is questionable whether the compression technology used will meet the increased requirements for HDTV.

The Chinese answer for HDTV applications is called EVD (Enhanced Versatile Disc). As with the case of HD-DVD-9, EVD is based on the current red-laser technology. EVD uses a new, high-level compression system called VP6, developed by New York-based On2 Technologies, to squeeze 120 minutes of HD movie footage onto a single disc.

While all formats are physically incompatible, they all bring about a large jump in data storage because of the same blue laser technology. On the other hand, it ‘s very possible that there is going to be a major fight between the two groups supporting the AOD and BD technologies. This cannot be avoided, because the financial rewards that the winner will obtain will be immense. Unfortunately, the end-user, as usual, will be the immediate loser, at least for the first couple of years.



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