DVD Overview

Pioneer began development of a new digital video disc format in 1991, with the goal of recording two or more hours of high-quality video on one disc, as a next-generation replacement for the LaserDisc.
In 1994, Pioneer introduced to the market an industrial model called the a Karaoke System, which could store and play back 2.1 GB of MPEG-1 data from a one-sided, 1.2 mm thick disc, using a 680 nm laser. In 1994, Pioneer also developed another digital video disc system which used an SHG blue laaser. In response to Hollywood’s desire to have this kind of new system enter the market before multi-channel satellite broadcasting, Pioneer worked with Toshiba to propose a disc specification called SD, which used a red laser, at the end of 1994. Around the same time, Sony and Philips were promoting the MMCD specification. The major difference between the SD and MMCD specifications were whether the discs should use two 0.6 mm substrates bonded together, or a single 1.2 mm substrate, as an extension off the CD format. At the end of 1995, agreement was finally reached on a specification that combined the two-substrate approach of SD with the 8/16 modulation of the MMCD specification. At this point the DVD Consortium was formed, and DVD truly go

ot started
In August 1996 the DVD Video Book was published, and the first DVD video players went on sale in November of the same year. The 3.95 GB Write-Once DVD-R Book, and the 2.6 GB rewritable DVD-RAM Book, were published in 1997. A DVD-RW Book and DVD-RAM Book, which define 4.7 GB rewritable formats, were published in 1999. A specification for 4.7 GB DVD-R was introduced in 2000. Two application specifications, the DVD Audio and the DVD Video Recording specification, were introduced in 1999. Following these specifications, DVD audio players, which provide high-quality multi-channel audio, and DVD video recorders, which allow recording to and playback of DVDs, were introduced to the market.

DVD Overview
.1 DVD History

Pioneer began development of a new digital video disc format in 1991, with the goal of reecording two or more hours of high-quality video on one disc, as a next-generation replacement for the LaserDisc.

In 1994, Pioneer introduced to the market an industrial model called the Karaoke System, which could store and play back 2.1 GB of MPEG-1 data from a one-sided, 1.2 mm thick disc, using a 680 nm laser. In 1994, Pioneer also developed another digital video disc system which used an SHG blue laser. In response to Hollywood’s desire to have this kind of new system enter the market be

efore multi-channel satellite broadcasting, Pioneer worked with Toshiba to propose a disc specification called SD, which used a red laser, at the end of 1994. Around the same time, Sony and Philips were promoting the MMCD specification. The major difference between the SD and MMCD specifications were whether the discs should use two 0.6 mm substrates bonded together, or a single 1.2 mm substrate, as an extension of the CD format. At the end of 1995, agreement was finally reached on a specification that combined the two-substrate approach of SD with the 8/16 modulation of the MMCD specification. At this point the DVD Consortium was formed, and DVD truly got started.

In August 1996 the DVD Video Book was published, and the first DVD video players went on sale in November of the same year. The 3.95 GB Write-Once DVD-R Book, and the 2.6 GB rewritable DVD-RAM Book, were published in 1997. A DVD-RW Book and DVD-RAM Book, which define 4.7 GB rewritable formats, were published in 1999. A specification for 4.7 GB DVD-R was introduced in 2000. Two application specifications, the DVD Audio and the DVD Video Recording specification, were introduced in 1999. Following these specifications, DVD audio players, which provide high-quality multi-channel audio, and DVD video recorders, which allow recording to and playback of

f DVDs, were introduced to the market.

1.2 Concepts and Structure of the DVD Format

A basic concept behind the DVD format is that, regardless of application, the physical format and file format should be common to all DVDs. (In the CD arena, formats differ between audio and data CDs.)

Structure of the DVD Format
The following table shows the relationship between the application format and the corresponding disc file format (as of 4/26/2001).

* See Chapter 3 for more information on the UDF Bridge file format
* Video Recording is a real-time video recording format, which gives attention to editability

Read-only DVD discs have the same logical and file format, regardless of application. These formats are defined by the DVD-ROM Book. Read-only discs for computer use fall into this category.

The video format for read-only discs is defined by the DVD-Video Book. Similarly, the audio format is defined by the DVD-Audio Book; however, this specification also includes a subset of the video format.

The DVD-R format is a write-once format. Because one application of DVD-R is to test read-only disc software in the authoring process, DVD-R uses the same UDF Bridge format as read-only discs. A key feature of DVD-R is that after it has been recorded, it has es

ssentially the same characteristics as a read-only disc. There are two specifications which define the 4.7 GB DVD-R format: the DVD-R for General, and the DVD-R for Authoring, specifications.

There are two formats for rewritable discs, DVD-RAM and DVD-RW. DVD-RAM uses a physical format which is designed primarily for random access. For this reason, its format utilizes zone CAV with pre-addressing. DVD-RW, on the other hand, is an extension of DVD-R, and uses a physical format designed primarily for sequential recording. This format makes it easy to achieve physical compatibility between DVD-RW and read-only discs.

The Real-Time Video Format allows these rewritable discs to be used for real-time video recording without an authoring step, and allows editing after recording. This format is different than the video format for read-only discs, which assumes that the content will be edited before recording. All these rewritable disc formats incorporate copyright protection systems to prevent illegal copying.

The video specification was revised in December 2000, making it possible for the video format to be used with DVD-R for General and DVD-RW, as well as for ROM. This is an extension of the video format for use in consumer recording applications, and allows recording only of non-protected content. This application was specified for DVD-R for General and DVD-RW while preserving format compatibility with DVD-ROM, in both the file system and application levels. Further, a new recognition method was defined for distinguishing DVD-R or DVD-RW from DVD-ROM disc applications (DVD video discs). (Supporting playback of DVD-R / DVD-RW discs with this type of content is optional for manufacturers of DVD playback devices; there are DVD-Video players, DVD-ROM drive equipped PCs, and other DVD playback devices that do not play DVD-R or DVD-RW discs recorded in Video Mode.)

Application of this video specification to the DVD-RAM format is under consideration. (As of July 2001)
1.3 The Future of DVD

Next-generation optical disc systems using blue lasers (with wavelengths around 405 nm) are under investigation. It is anticipated that such systems would be able to record two or more hours of high-definition video stream, as from digital satellite broadcast. This requires capacities of 20 GB or more. To achieve this high capacity, discs and pickups with different structures than those used in DVD are under investigation. For instance, lenses with NA of 0.85 (DVD uses NA of 0.6) and a transparent layer 0.1 mm thick (DVD uses 0.6 mm) may be required.

Some types of discs, such as dual-layer DVD discs, are just not compatible with the blue wavelengths. This will require optical systems with two wavelength light sources to maintain compatibility with current DVD discs (three wavelengths to maintain compatibility with CDs). How next-generation optical disc systems will maintain backward compatibility with the current DVD specification is still an open technical issue.

Pioneer is energetically pursuing the development of a blue laser system. Below is a list of documents which publish the successes achieved at Pioneer in the development of a blue laser system.

Pioneer presentations regarding next-generation DVD development:
1. High Density Optical Mastering Using Photobleachable Dye (JSAP, Fall 1996)
2. High Density Optical Mastering Using Photobleachable Dye, Part 2 (JSAP, Spring 1997)
3. High Density Optical Disk Mastering Using Photobleachable Dye (ISOM, 1996)
4. Process Margin of 15 GB Disk Mastering Using Photobleachable Dye (ISOM, 1998)
5. Investigation of High Density Mastering Using Electron Beam (JSAP, Fall 1996)
6. Investigation of High Density Mastering Using Electron Beam (II) (JSAP, Spring 1997)
7. Investigation of High Density Mastering Using Electron Beam (III) (JSAP, Fall 1998)
8. High Density Mastering Using Electron Beam (MORIS/ISOM’97)
9. Investigation of High Density Mastering Using Electron Beam (IV) (JSAP, Spring 2000)
10. High Density Recording Using Electron Beam Recorder (ODS, 2000)
11. High Density Recording Using Electron Beam Recorder (ISOM, 2000)
12. 25 GByte Read-Only Memory Disk Fabrication Process (ODS, 2001)
13. 27.4 GByte Read-Only Dual Layer Disk for Blue Laser (ISOM/ODS, 1999)
14. Super High Density Optical Disk by Using Multi-Layer Structure (ODS, 2000)
15. 50 GByte Read-Only Dual-Layer Disk for the High-NA Objective Lens and Blue-Violet Lasers (ODS, 2001)
16. High Resolution NROO Detection in Ultra-High Density Mastering Equipment (JSPE, 2001)
17. Relationship Between Developing Time and Bit Form in an Electron Beam Mastering Process (JSAP, Spring 2001)
18. Investigation of Warping Reduction in Thin Substrates Using Quick-Cool Molds (JSAP, Spring 1997)
19. Investigation of Warping Reduction in Thin Substrates Using Quick-Cool Molds (II) (JSAP , Fall 1998)
20. Investigation of High-Density Signal Replication Using a UV Sheet (JSAP, Spring 2000)
21. Optical Disc Processing, One Step Ahead (JSPP, 2000)
22. Improved Characteristics of Optical Disc Substrate Forming Using Ultrasonic Injection Moulding (Part 2) (JSPP, 2000)
23. Analysis of Causes of Warp in Optical Discs (Plastic Forming and Processing Conference, 2000)
24. Investigation of Birefringence Control in Thin Substrates (II) (JSPP, 2000)
25. 25 GByte ROM Disk by Injection Moulding (ISOM, 2000)
26. Large Capacity ROM Disk by Conventional Injection Molding Process (ODS, 2001)
27. High Density Phase Change Optical Disk Using Limit Equalizer (PCOS, 2000)
28. First Trial of the Groove Recording Disk for High-NA Objective Lens Using Electron Beam (ODS, 2001)
29. Disk Tilt Compensation Using Liquid Crystal (JSAP, Spring 1996)
30. Disk Tilt Compensation Using Liquid Crystal (II) (JSAP, Fall 1997)
31. Tilt Servo Using Liquid Crystal (JSAP, Fall 1997)
32. DVD/CD Compatible Pickup with Aberration Compensation (JSAP, Fall 1997)
33. Pickup Astigmatism Compensation Using Liquid Crystal (JSAP, Fall 1998)
34. Application of Liquid Crystal to Optical Discs (OSJ, 2000)
35. Tilt Servo Using a Liquid Crystal Device (ISOM/ODS, 1996)
36. 15 GByte DVD System Using a Liquid Crystal Panel (ISOM, 1998)
37. New Liquid Crystal Panel for Spherical Aberration Compensation (ODS, 1999)
38. Photo-Polymer Objective Lens for Blue Laser Disk System (ISOM, 2000)
39. Investigation of New Servo Error Detection Methods (Part 2) (JSAP, Fall 1999)
40. High North America Objective Lens for Blue Laser Disk System (ISOM, 2000)
41. Objective Lenses for Red and Blue Lasers (ODF, 2000)
42. Signal Simulation of 25 GB Read-Only Optical Disk System Using High-NA Objective Lens (ISOM, 2000)
43. Analysis of Jitter for Land/Groove Phase Change Disk (ISOM, 2000)
44. The Path from DVD (Red) to DVD (Blue) (MORIS/ISOM, 1997)
45. High-Density Reproduction System Using a Cross-Talk Canceler (MORIS/ISOM, 1997)
46. A New Equalizer to Improve a Signal-to-Noise Ratio (ISOM, 1998)
47. High-Density Optical Disc Playback Equipment Using a Cross-Talk Canceler (JSAP, 1998)
48. Signal Processing for 15 / 27 GB Read-Only Disk System (ISOM/ODS, 1999)
49. Tolerance of 3 Beam Cross-Talk Canceler (ODS, 2000)
50. 25 GB Read-Only Disk System Using the Two dimensional Equalizer (ISOM, 2000)
51. Next-Generation DVD System (LSJ, 2001)

Chapter 2 Physical Format of Read-Only Discs
2.1 Design Concept of the Physical Specification

2.1.1 DVD design target

The basic design of the DVD began with the goal of media for movies as content. Therefore, a basic goal was for a playback time of about 133 minutes, which is long enough to allow most movies to fit on a single disc.

However, since DVD was intended as a technology to replace LaserDisc (LD), DVD needed to provide at least equivalent video quality. As the result of many rounds of video quality evaluation, and with the assumption that DVD would use variable-rate video compression, it was determined that a data rate of 3.5 Mbps was the minimum requirement. Then, considering audio quality, flexibility for international use, and multimedia capability, it was decided to provide capacity for Dolby AC-3 audio in three languages (384 kbps x 3) and subtitles in four languages (10 kbps x 4), resulting in the design of a specification which required a disc capacity of 4.7 GB.

The difference between the DVD specification and the CD specification is not just the move from a near-infrared laser to a red laser; the difference is that the entire specification is designed to achieve a disc capacity of 4.7 GB, based on the evolution in technology in the ten-plus years since the CD was introduced in 1982. For instance, requirements for parameters such as disc eccentricity (radial run-out) and tilt have become considerably more strict than in the CD specification. This recognizes evolution in disc manufacturing technology, as well as the fact that the recording density has increase proportionally more than the laser wavelength decreased, reducing total system margin.

For example, the standard CD track pitch is 1.6 microns. Reducing this by the ratio of DVD to CD laser wavelength (650/780) would result in a 1.33 micron track pitch. However, DVD actually requires a track pitch of 0.74 microns, meaning that tracks are considerably more packed than one might expect. As the track pitch decreases, crosstalk increases, and the radial tilt margin is severely reduced. In order to achieve the required density the average track pitch variation was tightened to 0.01 microns. To reduce crosstalk the maximum allowed variation was also tightened to 0.03 microns.

To satisfy this specification, of course, it is necessary for the disc mastering equipment to be sufficiently precise, and the variability in playback device mechanisms and pickups must also be more tightly controlled than in CD players.

The specification known as DVD Book Part 1 describes the physical characteristics of a ROM disc needed to achieve such a system design. That is, the specification describes such things as the required disc mechanical properties, optical properties, and properties of the signal generated upon playback, as well as things like the modulation methods and error correction required to design DVD hardware. The DVD specification also allows dual layer discs and small ( 8 cm) discs; these definitions are also contained within this specification.

Note:
This information is based on DVD Specifications for Read-Only Disc: Part 1 PHYSICAL SPECIFICATIONS, version 1.03. Disc and equipment designers should refer to the most recent versions of the relevant specifications. Pioneer makes no warranty concerning the accuracy of information presented in this article, and is not liable for any damages suffered as a result of any inaccuracies contained herein.

2.1.2 UV-LBR and the use of 0.6 mm substrates
Simply put, the difference between a 4.7 GB DVD and a CD is in the recording density. Below are electron microscope photographs of features called “pits” recorded on CD and DVD media.

From these photos, it is easy to see how much smaller the DVD pits are. The problem is how to record and play back the information from these tiny pits.

CD and LD cutting is done with a mastering machine called a Laser Beam Recorder (LBR). These machines use light sources consisting of argon lasers with 457 nm wavelengths, or helium-cadmium lasers with wavelengths of 442 nm. To increase the recording density for DVD discs, LBRs have been developed which use argon or krypton lasers with near-ultraviolet wavelengths of 351 nm.
For playback, DVDs require a more tightly concentrated light than CDs do. The playback beam size is proportional to /NA, so DVD players need the numerical aperture (NA) to be large and the wavelength ( ) to be small in order to realize the tiny playback beam necessary. However, a problem arises when the disc is inclined, or tilted, with respect to the light source. A tilted disc surface cause an optical degradation known as coma aberration, which causes the light spot to be distorted and interferes with correct playback. The degree of coma aberration is proportional to d x NA3/ , where d is the disc substrate thickness. DVDs use a substrate that is 0.6 mm thick, compared to 1.2 mm used in CDs, thus reducing the effect of this degradation due to disc tilt by a factor of 2.
The figure above shows the relationship of disc tilt to coma aberration.

2.1.3 Issues with 0.6 mm substrates
A 0.6 mm substrate is not physically strong enough, and so it is necessary to bond two 0.6 mm substrates together to form a 1.2 mm substrate. This adds a bonding step in addition to the steps that are required to form the 1.2 mm substrate used in CD media. This extra step tends to increase substrate cost. However, since the substrate is thinner, the cooling time needed in injection molding is shorter. This reduces the cycle time required between injecting the disc material and removing the formed disc. Since a large percentage of the disc cost is the amortization of the manufacturing equipment, the shorter cycle time makes up for the addition of the bonding step, allowing a DVD to be produced for about the same cost as a high-density 1.2 mm substrate.

Further, the DVD specification provides for dual layer discs, which are extremely well-suited to this bonding process, which in turn leads to additional added value.

The next issue that arises is compatibility with CDs. CDs use 1.2 mm substrates while DVDs use 0.6 mm substrates, and the pickup must account for the difference in spherical aberration resulting from this difference in thickness. This can be accomplished using devices which have already been announced, such as dual-focus pickups, dual-lens pickups, or pickups which use liquid crystal devices to provide variable apertures.

Finally, 0.6 mm substrates are at a disadvantage when it comes to surface dirt and damage. Since the pickup beam diameter at the disc surface is only one-half that of the diameter for the 1.2 mm substrate, the DVD pickup is twice as sensitive to surface dirt and damage. This disadvantage is compensated for by using powerful error correction schemes. The CD format provides correction for error bursts up to 2.29 mm long, while the DVD format can correct for error bursts as long as 6.0 mm & more than twice as long. And when it comes to scratches, the CD information layer is covered only by protective lacquer and the printed surface, making the information layer quite vulnerable to scratches on the label side. The DVD, on the other hand, is actually composed of two bonded substrates. Since the information layer is protected by a full 0.6 mm substrate, it is much less vulnerable to label-side scratches than a CD.

2.1.4 Design for margin
The DVD design target is that when the worst-case disc allowed by the specification, considering the economics of production, is played using the worst-case pickup that can be produced in volume economically, the byte error rate after error correction will still be 1 x 10–20, which is good enough to be acceptable for computer applications.
Since the above target is for “after error correction,” the error correction capability must be calculated. Considering the tradeoff between error correction capability and the overhead of the added redundancy, the DVD format was set to one ECC block per 32 kB. This requires a byte error rate before correction of 1 x 10-2.
In order to achieve good economy on both the part of the discs and the playback mechanisms, and many experiments were performed. The current disc tilt specification was determined as a result of the efforts on both sides.
As will be explained hereafter, it is difficult to make the error rate a specification of the disc itself. Therefore, a jitter standard is set by the DVD specifications. A simple calculation based on a normal distribution requires that the jitter rate be under 15.4%, and experimental results indicate that jitter must be under 16%, to achieve the required error rate. Since the disc tilt varies within a revolution, it was decided to adopt the design concept that jitter must remain within 16% at the instantaneous peak value of tilt. Since it is actually very difficult to measure the peak value, the concept became to measure the average jitter at under 15%, and the byte error rate at under 5 x 10-3.
The basic concept of system margin is shown in the figure below. In the figure the horizontal axis indicates tilt, while the vertical axis represents jitter.
First, let’s consider the best results obtained from many experiments. If there is no tilt, then the jitter value includes components from light source noise, circuit noise, disc noise, standard interference between symbols (inter -symbol interference), and some small amount of crosstalk from the neighboring tracks.
Next, let’s find the minimum jitter level due to disc manufacturing variations other than tilt. Experimental results indicate that 8% is a reasonable value, based on the DVD specification.
Next we consider manufacturing variation in the circuitry.
Variation due to the disc and the circuitry have noise-like characteristics, and increase the minimum jitter level, but are thought to have a very small effect on tilt margin. Factors such as offset in the servo circuit, however, both increase the jitter level and decrease tilt margin. The figure shows the components of the reduction in margin, based on experimental results and past volume manufacturing experience. The remaining components are allocated to disc tilt and pickup tilt (including aberrations), resulting in the current specification.

2.1.5 Tracking error signal
The pits on CDs are typically about /6 deep. This enables the use of both a push-pull tracking error scheme, which works best at a pit depth of /8, and three-beam and differential phase tracking methods, which work best at a pit depth of /4. In the DVD specification, however, the top priority was to increase recording density, and so the specification was developed assuming the /4 pit depth necessary to obtain optimal signal quality. A push-pull signal is too small to be usable at a /4 pit depth, but the push-pull scheme has problems with offset due to lens shift and disc tilt anyway, so it was decided that support for that scheme was not important.

The differential phase tracking method, however, met all the requirements for compatibility, including handling dual layer discs and different track pitches. Further, this method was felt to be well suited to future recording density increases, and thus it was chosen as the standard tracking method for DVD. The differential phase tracking method does have the weakness of producing an offset in regions where there is strong correlation in bit pattern with the neighboringtracks , but this can be avoided by scramblingthe signal.
Dual layer discs
The DVD specification provides for dual layer discs, in a such a manner that either layer can be played without the need to turn over the disc. This gives rise to problems such as increased spherical aberration due to different substrate thickness when reproducing a signal from the different layers, and a decrease in signal-to-noise ratio due to reflected light from the surface not being played (inter-layer crosstalk). Track density is reduced by about 10% in dual layer DVD discs as a means of increasing margin.

The two layers need to be far enough apart that inter-layer crosstalk is small for standard pickups, but close enough that spherical aberration doesn’t become fatal. With this in mind experiments were performed, and the inter-layer distance was specified to be 55 15 microns. The substrate thickness specification for dual layer discs was able to be made thin because the thinner the substrate, the easier it is to control coma aberration, thus giving plenty of margin.

2.2 Features of the DVD Physical Specification

2.2.1 Standard evaluation specifications
The table below shows a comparison of the basic specifications used in evaluating specification compliance for CD and DVD discs. As shown in the table, the NA value is considerably larger for DVD. Since these are standard evaluation specifications, the limits on variability are quite tight. Further, there are specifications for items which were not specified for CDs, such as servo characteristics and transfer characteristics of playback system elements like laser diodes and waveform equalizers. Since the recording density is higher in DVD, the shortest mark is shifted toward the high range of the MTF low-pass optical system transfer function. The DVD has an MTF of 68%, compared with 50% for a CD system. As a result, the system requires waveform equalization for demodulation. Because the waveform equalization function changes the error rate and jitter value, the playback system transfer characteristics are set, including the waveform equalization function of a standard test device. As a result, it is possible to indirectlyspecify the performance of the LBR master recording device. The DVD specification also defines standard servo characteristics. These are closely related to the disc mechanical characteristics, which will be described later. For CDs, disc surface deviation and radial deviation are specified as accelerations. However, it is difficult to measure acceleration and produce repeatable measurement values. This issue was investigated during the work on the ISO 3.5″ disc. The result was to specify standard servo characteristics and to specify disc mechanical properties with the residual error after servo compression. The key feature of this method is the ability to generate repeatability of data. The DVD specification uses the same method. In specifying servo characteristics, open-loop specifications were avoided, as they are subject to wide variation; instead, closed-loop parameters were specified. Please refer to the DVD specification for playback system transfer characteristics and servo characteristics.
Further, the detector size is specified for measurement of dual layer discs. This is done with the intent of limiting the amount of inter-layer crosstalk. Care must be taken, as use of a larger detector will introduce obstacles to other measurements, particularly to reflectivity measurements, due to inter-layer crosstalk. As a side note, detectors usually utilize PIN photo diodes, and electrons excited by light entering from other than the detector portion can result in a considerable DC offset. Therefore, during measurement the detector should be shielded from stray light, or grounded to bleed off the stray electrons.
Comparison of standard evaluation specifications

DVD CD
wavelength 650 5 nm
780 10 nm

NA 0.60 0.01
0.45 0.01

polarization circular –
light intensity
at the rim
(of the pupil of
the abjective lens) RAD:60-70%
TAN:90% or more 50% or less
surface aberration 0.033 RMS or less
0.07 or less

laser diode noise -134 dB/Hz or less –
measuring scanning velosity 3.49 0.03 m/s (single layer)
3.84 0.03 m/s (dual layer)

disc clamping force 2.0 0.5 N
1-2N
circuit characteristics standard servo, equalizer, PLL,
CLV servo, slicer characteristics –

2.2.2 Jitter specification
The DVD specification includes a standard for jitter, which is not found in the CD specification. The logical format specifies disc mechanical and optical characteristics, but specifications for sources of degradation, like inter-symbol interference introduced in the disc cutting step, are not included in the current CD specification. There are also items which cannot be expressed by parameters listed in the current CD specification, such as degradation introduced by the mastering machine or unevenness in pit replication.
These effects can’t be ignored in DVDs with their higher recording density, and thus it is necessary to specify such factors. There was an error rate specification in the CD specification, but this is impossible to measure unless there are defects or degradation due to the playback device.
The disc specification for Pioneer’s Karaoke System specified an error rate using a tilted pickup, but this was a difficult measurement to make, and certainly not efficient. In the DVD specification it was decided to add a jitter specification, as jitter is a parameter where degradation can be measured numerically. Jitter is measured in the absence of tilt, which is an ideal disc specification, but it isn’t practical to compensate for tilt at all points. Since the effect of jitter due to the varying component of surface tilt is small, it was decided to measure across one full revolution and measure the average value of tilt variation. As a result, it is only necessary to compensate for the average radial tilt when taking measurements.

2.2.3 Tilt specification
The disc tilt limit is 0.8 in the radial direction, and 0.3 in the tangential direction. The specification for the radial direction is larger in consideration of the fact that it’s easy for the disc to curve into a bowl shape.

Note that the tilt angle defined by the specification is not just the physical angle of inclination, but rather the angle between incident and reflected light ( ), measured optically.

Of course, the specification defines characteristics of discs when shipped from the factory; but it also requires guaranteed disc characteristics after being subject to conditions in the marketplace. However, there are a wide variety of environmental conditions in the marketplace, making that very difficult to specify. Therefore, an Informative Annex to the DVD specification describes the minimum environmental tests. Care must be taken, for example, not to use adhesives that will degrade at the specified high temperatures.

As a side note, there have been reports of degradation due to disc tilt resulting from the use of improper cases and packing.

2.2.4 Reflectivity specification
For CDs, the reflectivity specification is for a disc with a reflective surface only, with no information recorded on the disc; practically speaking, this is very difficult to test. The DVD specification takes into account the player design, and specifies reflectivity in terms of the maximum playback signal level I14HThis is very easy to measure. In this case there are effects from disc birefringence, so the specification defines values for both polarizing and non-polarizing optical systems.

There are actually two sets of reflectivity specifications, as reflectivity differs between single layer and dual layer discs. For the polarizing optical system, the specified values are 45-85% for single layer discs, and 18-30% for dual layer discs. However, note that there are specifications for I14Hvariations across the surface and around a revolution, for the purpose of limiting variation in servo gain.

Further note that the minimum I14Hreflectivity value for DVD-RAM discs is about 10%. For more detailed information, please refer to the DVD-RAM specification. Ordinarily, the detection of whether or not a disc is loaded in a tray is done by attempting to focus on the disc. This means that the focussing mechanism must handle discs with a reflectivity of only 10%.

2.2.5 Tracking specification
The DVD specification adds an item for a crosstalk signal which expresses the contrast when cutting across a track, and which is used in pulling in of tracking and disc access. Since the track pitch is narrow and crosstalk noise is high, the crosstalk signal is specified to be measured after running through a 30 kHz low-pass filter.

2.2.6 Other disc parameter specifications
The table below shows the difference in some other parameters between the CD and DVD specifications. When playing video from a DVD, the disc spins at a rate which provides a linear speed of 3.49 m/s. (The linear speed of a CD is 1.2 to 1.4 m/s.) If disc warpage and eccentricity is the same for a DVD disc as for a CD, it would require a high bandwidth actuator to allow the pickup to follow the disc movement. This would raise the further complication of increased heat generation. This must be avoided to enable portable applications, and so the DVD specifications for disc eccentricity and surface deviation were made more strict than for CDs. Note that for dual layer discs the layer closest to the pickup is aligned during the clamping process. Therefore, the maximum eccentricity value is large, considering the de-center that can occur during bonding with the other bonded layer.

DVD CD
track pitch 0.74 0.01 m (average)
0.74 0.03 m (instantaneous)
1.6 0.1 m

eccentricity
(radial runout) 100 m peak to peak
140 m peak to peak

warpage
(surface deviation) 0.3mm

0.5mm

Since the DVD medium is a bonded disc, there must be a specification for the maximum allowable de-center in the bond. Since the specification includes variation in mass, a specification item for dynamic balance was created.

Further, so that the back side of the tapered cone used during clamping doesn’t contact the inside diameter of the disc, and so that no problems occur if a DVD is accidentally loaded into a CD player, the inside diameter is specified to not be less than 15.0 mm when viewed through both surfaces.

To maintain bonding strength, the maximum value of the depression on the inside of the clamping area was changed to 0.1 mm, from the CD value of 0.2 mm. And, considering LD and DVD compatible players, the maximum value of the stack ring thickness variability area protrusion on the outside of the clamping area was changed to 0.25 mm, from the CD value of 0.4 mm.

The program start radius of a CD is 25 mm. This was reduced to 24 mm for DVD to increase the disc capacity. The lead-in start radius is 22.6 mm. The maximum radius of the program region is 58 mm, followed by a lead-out of at least 0.5 mm width. Further, in order to insure that there is some region with program recorded, the minimum value of the outer radius of the information region is required to be 35 mm.
2.3 The DVD Data Format

2.3.1 ID, IED, and EDC
The figure below shows the process used in encoding.
First, two bytes of error correction code are added to a four-byte ID. This is done to enable fast access by making it easy to read the ID using only the ID’s error correction code, without having to calculate and check the error correction code which is later added to the entire data block. To this ID is added six bytes of control data, 2048 bytes of main data, and a four-byte EDC code. This EDC code is used for checks such as determining whether scrambling has been performed correctly, and whether error correction has occurred after the error correction code is calculated and checked.

2.3.2 Scrambling
After the EDC is appended, the data is scrambled. This is done to randomize the data and prevent problems like interference from a repeating pattern in the neighboring track, or a repeating pattern in the data resulting in a large DC component which affects the data slicing or servo. Note that the data used in the scrambling process will not have any fixed pattern, but will be comprised of 16 values, based on four bits in the ID, in a manner chosen to also be effective in recording. The initial value is taken from the four bits beginning with the fifth bit from the end of the ID, to provide the same scrambling to 16 sectors of data. Therefore, the scramble pattern makes one complete cycle in 16 x 16 = 256 sectors. This scrambling is done for the purpose of randomizing the data, which is particularly important for differential phase tracking. In differential phase tracking, a proper error signal cannot be generated if the pit arrangement in the adjacent track is in some particular pattern. At the inner circumference of the disc there are about 29 sectors around one complete revolution. Since the same scrambling continues for 16 sectors, the necessary condition has been met at the inside circumference. At the outer circumference there are about 70 sectors in one complete revolution. This is less than a full cycle of 256 sectors, so again the necessary condition has been met. The conditions will still be met a blue laser is used to increase recording density by a factor of 1.5. ECC encoding is done on the scrambled 16 sectors, using product codes.

2.3.3 ECC (Error Correction Code) block and interleaving

The figure above shows the data in block structure after ECC has been added, with 10 bytes of Reed-Solomon check code (182, 172, 11) added to each row of 172 bytes, and 16 bytes bits of Reed-Solomon check code (208, 192, 17) added to each column of 192 bytes .
After the ECC has been added, each of the bottom 16 rows is interleaved with the data so that there are 12 rows of data followed by one row of parity check code, as shown in the figure at right. This block of 13 rows of 182 bytes each comprises one recording frame, before the addition of modulation and synchronization signals.

2.3.4 Sync Code
Each row of a recording frame is divided into two equal parts, and a 32-bit synchronization (SYNC) Code is added to each group of 91 bytes(91 x 16 channel bits= 1456 bits). The pattern of this SYNC Code field is
AAA*******0001000000000000010001
The latter part of this field is a combination of 14T and 4T. The Tmax in the data is 11T, so adding 3T to make a pattern of 14T in the SYNC field means that even if 11T becomes 12T due to an edge shift, and if 14T becomes 13T due to an edge shift, it will still be possible to distinguish them. After the 14T comes a fixed 4T, and with the previous having a gap of at least 4T, it is prevented from having symbol interference with the 14T. The AAA portion is chosen to be either 000, 001, or 100, depending on the relationship with the previous word (defined by the condition and the (d, k) limitation). The seven bits indicated by ******* are used in combination with the three AAA bits to form one of 32 different patterns, and assigned one of two different codes with different edge transition numbers for eight types of SYNC Codes ranging from SY0 through SY7. Utilizing the two codes with different edge transition numbers for each SYNC Code allows look-ahead DC control. (DC control is done by choosing the the one of the two types of SYNC Code which will result in a smaller DSVuntil the point where DC control is next performed.)
The figure at right shows the combination of the SYNC Codes for the 13 rows in a sector. Each sector begins with SY0, and each row is uniquely identifiable by the pattern of cyclically repeating SY1 through SY4 and SY5 through SY7 codes. Error correction codes are generated over 16 sectors. The ID information following the SY0 at the beginning of the block is read and recognized as an address which is divisible by 16. SY0, that is to say, the beginning of the sector, plays an important role in decoding the data.
Since the individual rows are uniquely identifiable in the sector structure, several rows can be read and the location of a coming SY0 can be calculated from the periodicity of the rows’ SYNC Codes. This makes it possible to interpolate and read the next ID, even if for some reason the SY0 code is unreadable. Key features of this sector block structure are the large error correction code block and the ability to determine the sector head even if the actual pattern is unreadable.
The SYNC Codes were defined to realize in just 32 bits the features described above, namely a 14T length SYNC pattern that is 3T longer than the Tmax in the data region, DC control, and the identification of the sector start.
The synchronization frequency of a standard test unit is based on the 27 MHz clock of the video system, and is divided down by (512 x 3) to 17.578125 kHz. Since the channel clock is one SYNC frame interval, or (91 + 2) x 16 = 1488 bits, the channel clock frequency becomes 27 MHz x 1488 / 512 / 3 = 26.15625 MHz.
The ID information added to each sector is comprised of four bytes. The lower-order three bytes contain the sector number. The upper byte provides a bitmap of information which the drive requires in real time, namely the sector format (ROM or RAM), tracking method (pit tracking or groove tracking), reflectivity (greater or less than 40%), disc region (lead-in, lead-out, or middle data), and layer information (layer 0, layer 1, other). Note that the layer information is contained in the lowest-order bits of the byte, putting it in a position to be considered as the upper bits of the sector number.

2.3.5 Lead-in, middle, and lead-out regions
The CD’s table of contents information is contained in the lead-in area, and contains a table of information used to access the rest of the disc. The DVD specification, however, adopts the concept that all information about the data content is contained within a file system, and exists within the data itself. Therefore, the information written in the lead-in (middle region) is information necessary only for the drive itself, such as disc compatibility and drive control information. (There are also regions for manufacturer information or related to copying.)
This information is called control data, and is written in the 17.5 to 105 tracks located inside the data region start radius of 24 mm. One block of the control data is an ECC block (16 sectors), and is written across 192 blocks, or in other words, is repeated 192 times. The first sector of the control data contains physical format information. The physical format information describes what type of disc it is, conforming to what revision of the specification. It also describes the disc size, the maximum transfer rate with consideration for portable players, number of layers, track path type, whether the disc is all ROM or partial ROM, recording linear density, track density, and start and end sector numbers.
Starting 16 tracks inside of the control tracks and covering two blocks of length is recorded a reference code used for equalizer calibration. Inside of this, ROM discs also contain a region of all-zero data extending inward to a radius of 22.6 mm.

3.1 Structure of the DVD-ROM Logical Format

The file format of the DVD-ROM family is common to DVD-ROM (computer applications), DVD-Video, and DVD-Audio discs. This makes it possible to handle the same content in the same way on both consumer-oriented stand-alone devices and computer systems.
However, there are a few minor restrictions on the file system for DVD-Video and DVD-Audio. This is to make it possible to play these discs on stand-alone devices which use simple software.

3.2 Overview of the DVD-ROM File Format

DVD-ROM uses the UDF (Universal Disk Format), but can also be accessed using ISO-9660, to provide compatibility with previous systems. This hybrid file system is called “UDF Bridge.” As both file systems are able to access any file on the disc, all content on the disc can be accessed by using either file system.

3.3 Relationship with the Application Format

The files used for DVD-Video and DVD-Audio are arranged in directories called VIDEO_TS and AUDIO_TS, respectively. The files in these directories have predetermined names and extensions. Files with the extension “.IFO” contain application information needed to reproduce the content. For each “.IFO” file there is always a back-up file with the same name but the “.BUP” extension. Files with the “.VOB” extension contain the actual video or audio content.

Chapter 4 Video Format
DVD-Video contains not only the actual video and audio content, but a variety of powerful information which enables features peculiar to the DVD format, such as multi-angle viewing, parental lock, random shuffle playback, etc., and also provides support for special playback modes such as fast forward and reverse. In this chapter, we will call the actual video and audio content the “presentation data,” and the special extra information the “navigation data.”
Chapter 5 Audio Format
5.1 Introduction

In February 1999, the DVD Forum formally approved the release of DVD-Audio Ver. 1.0, as a new format to handle next-generation audio. This was a result of three years of discussion in the DVD Forum’s Working Group 4, a technical working group comprised of many members of the hardware industry, music industry, and computer industry, as well as the ISC (International Steering Committee, composed of IFPI, RIAA, and RIAJ representatives of the world’s music industry). This makes the DVD-Audio specification truly a global standard.

5.2 Overview of the DVD-Audio Specification

DVD-Audio Design Concept
• Pure Audio: Linear PCM and Packed PCM (lossless encoding)
– extremely high quality
(192 and 176.4 kHz sampling frequencies, in stereo)
– multi-channel (scalable, up to six channels)
• Maintains compatibility with the DVD-Video format
• Many added features
– still image features
– video features (a subset of the DVD-Video format)
– centralized text, real-time text
• Access features suitable for audio systems
– access units leverage the familiar paradigm of conventional
audio media album (Volume), group (Title Group), track (song),
index (Cell)
– continuation of the basic concepts behind DVD-Video
– TOC-style access method (two-channel content)

5.2.1 DVD-Audio and DVD-Video formats

The DVD-Audio specification was established as the second ROM application format for the DVD family. In formulating the design concept, compatibility with the DVD-Video specification was given high priority, in addition to striving to meet the needs of next-generation audio discs. To this end, the physical format and file format were made common with the DVD-Video standard, but this is not all; the DVD-Audio specification also aims to share much in common with DVD-Video in its application format. The specification for audio data, the core of playback data for DVD-Audio, is comprised of portions compliant to the DVD-Video specification, portions which are extensions of the DVD-Video specification, and portions which were newly defined for DVD-Audio. The specifications for compressed audio and video are a subset of the DVD-Video specification & complying with that specification but with some additional restrictions added & thus maintaining complete data compatibility. Some portions of the specification for still images, menus, and text data follow the DVD-Video specification, but most portions are newly defined to provide more appropriate features for audio discs.

5.2.2 Discs and players

With the emergence of the DVD-Audio specification, it is anticipated that the DVD-Video players on the market will be joined by Audio-only players, which focus on providing the best possible sound quality; compatible players, which can play both DVD-Audio and DVD-Video discs; and many other specialized players to meet users’ needs, such as portable players and car audio devices. The DVD-Audio specification provides the capability for discs to include not only pure audio content but also video or still image content which can be played along with the audio content. The specification allows the audio portion of such video content to be played on Audio-only players, while the video can also be reproduced by pre-existing DVD-Video players.

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