1. DVD History
The following Technical Guide is dedicated to the DVD format and its releated technologies. The guide was written from the R&D Department of Pioneer. You can find the article at Pioneer's official website here.
Chapter 1 - DVD Overview
1.1 DVD History
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 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 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 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 DVDs, were introduced to the market.
2. Concepts and Structure of the DVD Format
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 essentially 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)
3. The Future of DVD
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:
||High Density Optical Mastering Using Photobleachable Dye (JSAP, Fall 1996)
||High Density Optical Mastering Using Photobleachable Dye, Part 2 (JSAP, Spring 1997)
||High Density Optical Disk Mastering Using Photobleachable Dye (ISOM, 1996)
||Process Margin of 15 GB Disk Mastering Using Photobleachable Dye (ISOM, 1998)
||Investigation of High Density Mastering Using Electron Beam (JSAP, Fall 1996)
||Investigation of High Density Mastering Using Electron Beam (II) (JSAP, Spring 1997)
||Investigation of High Density Mastering Using Electron Beam (III) (JSAP, Fall 1998)
||High Density Mastering Using Electron Beam (MORIS/ISOM'97)
||Investigation of High Density Mastering Using Electron Beam (IV) (JSAP, Spring 2000)
||High Density Recording Using Electron Beam Recorder (ODS, 2000)
||High Density Recording Using Electron Beam Recorder (ISOM, 2000)
||25 GByte Read-Only Memory Disk Fabrication Process (ODS, 2001)
||27.4 GByte Read-Only Dual Layer Disk for Blue Laser (ISOM/ODS, 1999)
||Super High Density Optical Disk by Using Multi-Layer Structure (ODS, 2000)
||50 GByte Read-Only Dual-Layer Disk for the High-NA Objective Lens and Blue-Violet Lasers (ODS, 2001)
||High Resolution NROO Detection in Ultra-High Density Mastering Equipment (JSPE, 2001)
||Relationship Between Developing Time and Bit Form in an Electron Beam Mastering Process (JSAP, Spring 2001)
||Investigation of Warping Reduction in Thin Substrates Using Quick-Cool Molds (JSAP, Spring 1997)
||Investigation of Warping Reduction in Thin Substrates Using Quick-Cool Molds (II) (JSAP , Fall 1998)
||Investigation of High-Density Signal Replication Using a UV Sheet (JSAP, Spring 2000)
||Optical Disc Processing, One Step Ahead (JSPP, 2000)
||Improved Characteristics of Optical Disc Substrate Forming Using Ultrasonic Injection Moulding (Part 2) (JSPP, 2000)
||Analysis of Causes of Warp in Optical Discs (Plastic Forming and Processing Conference, 2000)
||Investigation of Birefringence Control in Thin Substrates (II) (JSPP, 2000)
||25 GByte ROM Disk by Injection Moulding (ISOM, 2000)
||Large Capacity ROM Disk by Conventional Injection Molding Process (ODS, 2001)
||High Density Phase Change Optical Disk Using Limit Equalizer (PCOS, 2000)
||First Trial of the Groove Recording Disk for High-NA Objective Lens Using Electron Beam (ODS, 2001)
||Disk Tilt Compensation Using Liquid Crystal (JSAP, Spring 1996)
||Disk Tilt Compensation Using Liquid Crystal (II) (JSAP, Fall 1997)
||Tilt Servo Using Liquid Crystal (JSAP, Fall 1997)
||DVD/CD Compatible Pickup with Aberration Compensation (JSAP, Fall 1997)
||Pickup Astigmatism Compensation Using Liquid Crystal (JSAP, Fall 1998)
||Application of Liquid Crystal to Optical Discs (OSJ, 2000)
||Tilt Servo Using a Liquid Crystal Device (ISOM/ODS, 1996)
||15 GByte DVD System Using a Liquid Crystal Panel (ISOM, 1998)
||New Liquid Crystal Panel for Spherical Aberration Compensation (ODS, 1999)
||Photo-Polymer Objective Lens for Blue Laser Disk System (ISOM, 2000)
||Investigation of New Servo Error Detection Methods (Part 2) (JSAP, Fall 1999)
||High North America Objective Lens for Blue Laser Disk System (ISOM, 2000)
||Objective Lenses for Red and Blue Lasers (ODF, 2000)
||Signal Simulation of 25 GB Read-Only Optical Disk System Using High-NA Objective Lens (ISOM, 2000)
||Analysis of Jitter for Land/Groove Phase Change Disk (ISOM, 2000)
||The Path from DVD (Red) to DVD (Blue) (MORIS/ISOM, 1997)
||High-Density Reproduction System Using a Cross-Talk Canceler (MORIS/ISOM, 1997)
||A New Equalizer to Improve a Signal-to-Noise Ratio (ISOM, 1998)
||High-Density Optical Disc Playback Equipment Using a Cross-Talk Canceler (JSAP, 1998)
||Signal Processing for 15 / 27 GB Read-Only Disk System (ISOM/ODS, 1999)
||Tolerance of 3 Beam Cross-Talk Canceler (ODS, 2000)
||25 GB Read-Only Disk System Using the Two dimensional Equalizer (ISOM, 2000)
||Next-Generation DVD System (LSJ, 2001)
4. Design Concept of the Physical Specification
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.
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.
5. Features of the DVD Physical Specification
Chapter 2 - Physical Format of Read-Only Discs
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.
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.
The disc tilt limit is 0.8in the radial direction, and 0.3in 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.
|track pitch0.74 0.01 m (average)
0.74 0.03 m (instantaneous)
(radial runout)100m peak to peak
|140m peak to peak
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.
6. 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.
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
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.
7. Read-Only Disc File Format
Chapter 3 Read-Only Disc File Format
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.
8. Video Format
Chapter 4 Video Format
4.1 Video Format Overview
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."
4.2 VMG and VTS
The DVD-Video zone contains all the files necessary for playback of DVD-Video, and is made up of one Video Manager (VMG) and multiple Video Title Sets (VTS). The VMG is composed of VMGI(Video Manager Information), VMGM_VOBS (Video Object Set for VMG Menu), and the backup VMGI(BUP).
The VMGI consists of control information for the entire DVD-Video zone, and comprises a single file named VIDEO_TS.IFO.
The VMGM_VOBS contains the content necessary for the title selection menu, and comprises a single file named VIDEO_TS.VOB.
The VMGI(BUP) is a complete copy of the VMGI, and comprises a single file named VIDEO_TS.BUP.
VMGM_VOB may or may not exist, but the other two types of information are required.
Each VTS is composed of VTSI (Video Title Set Information), VTSM_VOBS (Video Object Set for the VTS Menu), VTSTT_VOBS (Video Object Set for Titles in a VTS), and the backup VTSI(BUP). The VTSI is control information for the VTS, and comprises a single file named VTS_##_0.IFO. The VTSM_VOBS contains the content for all types of menus within the VTS, and comprises a single file named VTS_##_0.VOB.
The VTSTT_VOBS contains the content needed for title playback, and comprises multiple files, named VTS_##_@.VOB.
The VTSI(BUP) is a complete copy of the VTSI, and comprises a single file named VTS_##_0.BUP.
VTSM_VOBS may or may not exist, but the other three types of information are required. In the file names above, ## represents a two-digit number between 01 and 99, and @ represents a single-digit number between 1 and 9.
4.3 Presentation Data
9. Video Format - Page 2
Within the presentation data, video, audio, and sub-picture data are multiplexed with a portion of the navigation data in conformance with the MPEG-2 program stream specification. The structure of pack and packet comply with this specification, and each pack contains 2048 bytes. The multiplex rate (mux_rate) is 10.08 Mbps.
|data compression method
||9.8 Mbps max. (MPEG-2)
1.856 Mbps max. (MPEG-1)
||36 fields max.
||pan & scan, letterbox
Video data exists as one stream of data compressed according to the MPEG-2 video format. The maximum bit rate is 9.8 Mbps, and the stream supports variable bit rate to provide high-quality video.
DVD-Video is compatible with both NTSC and PAL formats, and supports both 4:3 and 16:9 aspect ratios. The title creator can specify either "pan & scan" (cutting off a portion of the image) or "letterbox" (showing then entire image with black bands at the top and bottom of the screen) format to provide output of 16:9 aspect ratio video content at an aspect ratio of 4:3.
||16 / 20 / 24 bits
* Trademarks of Dolby Laboratories Licensing CorporationThree audio formats are allowed by the DVD specification: linear PCM, Dolby Digital, and MPEG audio. Each title can have up to eight audio streams. The streams are distinguished by attributes such as language. Each stream is comprised of multiple channels. For instance, the Dolby Digital format supports 5.1 channels.When using the linear PCM format, DVD audio can support a sampling rate of up to 96 kHz with up to 24 bits per sample, providing audio quality which far surpasses that of CDs. For Dolby Digital or MPEG audio, the sampling rate is 48 kHz. MPEG audio supports MPEG-2 audio with multi-channel capability.
||run-length encoding, two bits per pixel
|data size per picture
||52 kB max.
||16 colors (specified per PGC)
||change pixel contrast and color
change display area (move)
change display data (scroll up/down)
Sub-picture data is a concept peculiar to DVD, and consists of defining data, such as subtitles, menus, and karaoke lyrics, which is overlaid as a bitmap onto the main video content. This data is compressed using run-length encoding. Up to 32 streams of sub-picture data can exist for each title. Sub-picture streams are distinguished by attributes such as language.Sub-picture data can be displayed in up to 16 different colors. For applications such as subtitles, the user controls the display of sub-picture data. DVD also supports the forcing of sub-picture data display, for example if the title creator wants to force a menu to be displayed at a particular point in the content stream.
10. Video Format - Page 3
4.4 Navigation Data
4.4.1 Cells and PGCs
A cell is a unit of playback of real-time data. Each cell is identified with a fixed ID number. A Program Chain (PGC) defines the order in which cells are played back. That is, each PGC defines the order in which the cell numbers are to be played. A title is comprised of one or more linked PGCs. In a case such as a simple movie, where one title is comprised of one PGC, the cells recorded on the disc are played back in order, and so the cell numbers and cell ID numbers will be the same. If multiple titles with different stories in a title set are defined by their own PGCs, then each PGC will call out the cells to be played for that title and the order in which they are to be played, and the cell numbers and cell ID numbers will not be the same.
In this way, the DVD specification defines PGCs and cells to allow the order and time relationship of the real-time data playback to be essentially arbitrary. This structure can be utilized to provide playback options such as parental level selection, angle selection, and story selection.
Each PGC may also contain a pre-command, which is executed before playing back the first cell, and a post-command, which is executed after playing back the last cell. And the PGC may contain button or cell commands, which can be executed each time a cell is played. Through these commands and user operation, one PGC can branch into multiple PGCs, multiple PGCs can branch into the same PGC, etc., providing the possibility for many types of interactive playback.
4.4.2 Programs and PTTs
A sequence of one or more cells with consecutive numbers within a PGC can be defined as a program. Programs may be used as units of playback for random or shuffle playback, or to be accessed via commands.
Further, sequences of one or more programs with consecutive numbers within a PGC can be defined as a PTT. PTTs correspond to chapters, and are one unit of access provided to the user.
4.4.3 PCI and DSI
A cell is comprised of one or more Video Object Units (VOBU). Each VOBU consists of 0.4 seconds to 1 second of playback time. Each VOBU begins with a Navigation Pack (NV_PCK) and is followed by several Group Of Pictures (GOP) structures which contain video, audio, sub-picture, and other data in a packetized, time-division multiplexed fashion. However, a VOBU is not required to contain any data other than the NV_PCK, and thus the content within a VOBU may be shorter than the playback time of the VOBU itself. Further, the number of frames per GOP is not fixed, and if it is ended with an MPEG sequence end code, playback will be paused on the last frame of the GOP. This makes it possible to include still frames displayed for an arbitrary length of time at arbitrary points within video playback. Audio information may also be added to such sequences.
The NV_PCK is comprised of two packets, called Presentation Control Information (PCI) and Data Search Information (DSI).
In order for DVD players to support variable-rate playback and seamless playback, there is a large memory between the pickup and the decoder, called a track buffer. As a result, there is a time delay between the signal being read by the pickup and the video and audio being decoded and played. Therefore, real-time control information is divided between and stored within the PCI and DSI packets, and the player checks and utilizes those information after and before the cell passes through the track buffer.
11. Audio Format
Chapter 5 - Audio Format
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),
- 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.
12. Audio Format - Page 2
5.3 Audio Specification
| Major Features
- Super Hi-Fi stereo audio
- Scalable multi-channel capability
- Downmix control features
- Multi-channel to two-channel conversion
- Bit shift capability
- Audio selection features
- Attributes modifiable on a per-track (song) basis
5.3.1 Super Hi-Fi stereo audioAs a result of discussions with the music industry, the highest priority in the development of the DVD-Audio specification was given to the ability to perfectly reproduce the musical characteristics desired by music creators. That is, the producers of music strongly requested the features of complete transparency (that is, the playback sound quality is the same as the production sound quality), complete compatibility with the signal processing, editing, etc. capabilities of current and future studio equipment, and the ability to record past musical assets. As a result, linear PCM was chosen as the encoding scheme for the core audio content. Linear PCM is also used in DVD-Video, but as DVD-Audio gives even more weight to audio quality, the capabilities of DVD-Audio are considerably expanded to provide a 96 kHz bandwidth and a 144 dB dynamic range.
5.3.2 Audio specification details
| Linear PCM(Scalable)
Packed PCM (lossless encoding)
| Linear PCM
|| MPEG Audio
|Audio specifications for Linear PCM and Packed PCM encoding schemes
|Maximum number of channels
||6ch (fs: 48/96/44.1/88.2 kHz)
2ch (fs: 192/176.4 kHz)
(2ch for Stereo
+ 6ch for Multi channel)
|Maximum bit rate
(Linear PCM / Packed PCM)
( fs: 48/96/192 kHz)
(fs: 44.1/88.2/176.4 kHz)
(fs: 48/96 kHz)
As with DVD-Video, audio data in DVD-Audio is combined with header information and management information to form audio packets, which are then combined into 2048-byte packs. These packs are multiplexed with other packs to form Objects and are recorded to the disc. Two types of objects are specified by DVD-Audio. Audio Objects (AOB) are intended for use in main audio playback, while Video Objects (VOB) are used for playback of images and audio. The encoding methods defined for the two kinds of objects are different. The encoding method for VOB follows and is identical to the DVD-Video specification, to maintain compatibility with that format. The AOB format, however, uses a new Linear PCM (Scalable) and Packed PCM to provide higher audio quality.
In order to satisfy various requests from the music industry, the audio specifications for Audio Objects are based on the DVD-Video specification, with extensions to provide further capabilities.
Sampling rates that are multiples of 44.1 kHz were added to allow the recording of currently-existing music assets with perfect transparency and no processing required. Sampling rates of 196 kHz and 176.4 kHz were added to meet the ultra-high bandwidth demands of next-generation audio discs. The bit rate was expanded to 9.6 Mbps to support specification extensions for multi-channel audio, in addition to providing ultra-high bandwidth.
Lossless compression (Packed PCM) was added as a means to achieve 96 kHz, 24-bit, 6-channel (13.824 Mbps) recording and a greater than 74 minute recording length.
5.3.3 Data rate and recording time
DVD-Audio takes advantage of the large (4.7 GB) capacity and high (10.08 Mbps) transfer rate of the DVD format to make it possible to record extremely high quality audio content and multi-channel audio content that just wasn't possible with previous media. On the other hand, DVD-Audio also makes it possible to record over 400 minutes of CD-quality audio. The use of lossless compression further expands the recording time and effective transfer rate (to a maximum of 13.842 Mbps before compression).
5.3.4 Scalable multi-channel
One major benefit provided by the Linear PCM encoding used in the DVD-Audio specification is scalability. Even in actual multi-channel recording, the surround channel signals, which consist primarily of echo, typically have much lower levels than the front channel signals and also require less bandwidth. In such cases, it is possible to improve efficiency by recording the surround channel signals with lower sampling frequencies and quantization bit depths.
In this context, scalability is the concept of grouping the channels into multiple channel groups according to various parameters of the source data, and then setting the optimal sampling frequency and quantization bit depth for each channel group. A channel group is simply a set of channels which are encoded with a common sampling frequency and bit depth. For example, the front three channels could be encoded at 96 kHz, 24 bits per sample, while the rear two channels and LFE (Low Frequency Effect) channel could be encoded at 48 kHz and 16 bits per sample. Or front right and left channels and rear channels could be encoded at 96 kHz, 20 bits per sample, while the center and LFE channels could be encoded at 48 kHz with 20 bits per sample. The following restrictions apply to channel group audio specifications in DVD-Audio.
- There may be at most two channel groups.
- 192 kHz and 176.4 kHz sampling frequencies may not be used in conjunction with scalability.
- The sampling frequencies must have common factors.
- The sampling frequency and quantization bit depth for channel group 2 must be less than or equal to those of channel group 1.
There are 21 allowable configurations of channels assigned to channel groups, and the relationship between channels, groups, and speaker position is also specified. Even if the sampling frequency and bit depth are common to all channels, the channels must be assigned to two channel groups if there are three or more channels.
|Note 1: must include left and right front channels
Note 2: channel group 1 only, two channels max.
Note 3: if the sampling frequency differs between the channel groups, sample timing must be synchronized to the timing of the lower-frequency channel
|For LPCM audio sources.
||Two groups max. ( 9.6 Mbps)
||Sampling frequency, quantization bit depth of channel group 1 Sampling frequency, quantization bit depth of channel group 2
||May be changed on a per-track (song) basis
In addition to conventional stereo playback, DVD-Audio also supports multi-channel audio to provide new kinds of sound stages. These new sound stages, wherein each channel provides audio quality which far surpasses that of CD audio, should make music a more powerful experience for the listener than ever before possible. Practically speaking, however, all users may not have an environment which allows them to reproduce multi-channel sound. Further, there will be different kinds of listening environments, such as listening outdoors. For these reasons, the DVD-Audio specification was designed to provide robust support for both multi-channel audio and two-channel stereo, and thus provides for various ways to reproduce multi-channel content in two-channel environments.
One of these methods is called downmixing. Each disc which contains multi-channel audio content can have recorded on the disc the relationship between the various channels and the left and right channels (Lmix and Rmix) of a mixed-down two-channel audio stream. When such content is played, the player performs the downmix processing according to the following formulas.Lmix = 0Lf 1Rf 2C 3Ls 4Rs 5LFE
Rmix = 0Lf 1Rf 2C 3Ls 4Rs 5LFE
(indicates phase (180)The downmix coefficients and may only be set for Linear PCM data in the AOBs, and the values may be different for each track. The coefficients may be set in extremely fine steps, with a minimum step size of 0.2 dB. This allows the artist to provide audio playback with the exactly the desired feel.
5.3.6 Bit shifting
When the quantization bit depths of the channel groups are different in a multi-channel audio stream the player treats both digital full scale values as the same signal level. As a result, when reproducing the multi-channel audio the channels with less bit depth will have quantization noise that is relatively greater, and thus has a larger influence on the total dynamic range. The DVD-Audio specification incorporates a method called bit shifting to reduce this influence.
For instance, if the peak signal level for channel group 2 is less than -12 dB, the upper three bits will always have the same value as the MSB. This means that the signal can be shifted upward by two bits, which allows 18 bits of data to maintain the original 20 bits of precision. After channel group 2 signals are shifted upward, data for channel group 1 is recorded to the disc at 20 bits per sample, while the lower four bits of the channel group 2 signals are truncated and the signals are recorded at 16 bits per sample. At the same time, information indicating that channel group 2 has been recorded with a two-bit upshift is also recorded to the disc. During playback, the channel group 2 signals will be downshifted by two bits. That is, the MSB of the 16-bit data is expanded to add two high-order bits that are the same as the MSB, while two bits of zeros are added to the low-order end of the samples, producing 20-bit data for playback. This allows the precision of an 18-bit sample to be preserved, thereby increasing the dynamic range by 12 dB over what would be obtained by simply truncating the channel group 2 signals to 16-bit samples, and thus reducing the overall noise level. This bit shifting is done to increase the efficiency of sample usage and expand the dynamic range of Linear PCM multi-channel audio. It cannot be used with Packed PCM, and may only be applied to Linear PCM channel group 2 signals. Samples may be shifted by one to four bits, and the shift amount may be changed on a per-track basis. Bit shifting may not be used when both channel groups are using the same quantization bit depth. In combination with the scalability features, bit shifting provides efficient data transfer while maintaining maximum bit resolution for channel group 2 signals.
5.3.7 Audio Selection
|Audio selection playback example
AVTT = Audio Video Title (an audio title recorded in Video Format)
AOTT = Audio Only Title (an audio title recorded in the new Audio Format; LPCM, Packed PCM)
The DVD-Audio specification defines a feature called Audio Selection which allows support for audio data in two different formats in the same track. The user first sets up his system according to the playback capabilities of his player and playback system, and the player can then automatically select the correct audio data to play back between the two formats. The user may also specify the data to be played back, at playback time. Audio Selection is applicable to the following combinations of the two types of data (objects or streams).
- A combination of different numbers of channels (stereo, multi-channel)
- A combination of different encoding methods
- A combination of different numbers of channels and different encoding methods
13. Audio Format - Page 3
5.4 Additional Information
The DVD-Audio specification allows reproduction of a wide variety of audio content, from Super Hi-Fi stereo to multi-channel audio (5.1ch), which provides a powerful concert hall experience. But that's not all. DVD-Audio also defines various types of additional information which expands the world of audio entertainment, making it a specification truly worthy of the "next-generation audio disc" appellation. In consultation with content creators, the details of this additional information were refined again and again throughout the process of defining the format, as the specification evolved to its current form.
DVD-Audio defines three main types of additional information: 1) still image information; 2) video information; and 3) text information.
5.4.1 Still image information
Still images, as the term is used in the purview of DVD-Audio, is the feature which allows still images to be recorded to a DVD-Audio disc, and then displayed as images on a display of some kind while the audio is being played back, according to control provided by navigation data. When playing audio content which has associated still images, a data structure called an ASVU (Audio Still Video Unit), which contains the data for multiple still images, is first read from the disc and stored in buffer memory. After this is done, the audio data begins to play. As long as playback remains within the ASVU range (the range of content covered by the one ASVU in the buffer), the system can guarantee continuity of audio reproduction with no skips in the audio stream. That is, there is no need to stop the audio in order to read images from the disc. The specification defines several different playback modes which expand the possibilities for using still images.
Various playback modes are defined for still image reproduction, including display timing, display order, and a variety of visual effects. The content creator can select these modes to provide the user with the most effective possible presentation of the content.
The following playback modes are defined by the specification.(1) Display timing
- Slide show mode (still images are displayed one after the other, with timing defined by the content creator, as the audio is played)
- Browsable mode (still image display is independent from the audio playback, and the user can control the timing of still image display)
(2) Display order
- Sequential mode (still images are displayed in an order determined by the content creator)
- Random / shuffle mode (still images are displayed in an arbitrary order)
(3) Visual effects (optional)
- Cut in / out
- Fade in / out
18.104.22.168 Sequential slide show
This example illustrates a sequential slide show, which is a combination of sequential mode and slide show mode. In this mode, the still images are displayed in an order and timing to fit perfectly with the audio content, as determined by the content creator. While listening to the audio, the user can also view the images, which are matched to the audio, on a monitor.
22.214.171.124 Sequential browsable
This example illustrates sequential browsable mode, which is a combination of sequential mode and browsable mode. In this mode, the display order of the still images is determined by the content creator. The time at which the images are displayed is completely up to the user, who can move through the images like turning the pages of a book, moving at his own pace. In this example the basic order and timing are determined by the content creator, and if the user does nothing the images will be displayed in the predetermined order, and the display will move to the next image after a set amount of time passes. However, the user can specify "return to previous" or "go to next" at any time, and the previous or next image will be displayed in response.
14. Audio Format - Page 4
5.5 Video Information
| Subset of the DVD-Video format
- MPEG-1, MPEG-2
- 525/60 (NTSC), 625/50 (PAL, SECAM): same format for entire volume
- 16:9 / 4:3
- Pan & scan and letterbox features
- Closed caption features
- Sub-picture features
- Linear PCM required (48 or 96 kHz only; new specifications like scalability not supported)
- Compressed audio recording available as an option
- Two streams max.
- No parental control, regions, or interactive commands
- Seamless angle may be recorded only for the ATT defined as only AVTT.
Note: See Chapter 4 for more information on the DVD-Video format
5.6 Text Information
| Optional for discs, optional for players
Two types of text information
Centralized recording: static text information
Real-time: dynamic text information
- When text information is recorded, it must include album name, group name, and track names
- Other information, such as released date, artist names, etc., may also be recorded
- Allows easy content search, jacket-like text menu
- No limitation on language units
Character set code
- Recorded in the audio data recording region
- Displayed simultaneously with audio playback; smallest display granularity is one second
- Useful primarily for display of lyrics, liner notes
- Up to eight languages, defined when concentrated data is written, and limited to languages contained therein
- ISO8859-1 (Roman alphabet), Music Shift JIS (Japanese)
15. Audio Format - Page 5
5.7 Access system similar to conventional audio discs
The DVD-Audio specification defines a hierarchical structure and units of access, with the focus of continuing with the same style of operations used with familiar previous audio discs. As in the past, one song corresponds to one track. However, since one 12 cm single-layer disc holds 4.7 GB and is thus has the capacity to hold multiple CD albums, it is possible to record many tracks on a single DVD. To improve accessability, the DVD-Audio specification combines multiple tracks which should be played sequentially into a newly-defined access unit called a Group. A Group is a logical unit, and can form a large structure of one or more sequential Audio Titles (ATT) as a single playback unit. This logical unit can be played continuously with a single operation.
Audio Title is a logical structure which is equivalent to a Title in DVD-Video, and is comprised of the presentation data to be played and the navigation data which determine the playback sequence. Unlike its DVD-Video counterpart, Audio Title is a unit of access that the user will not be concerned with. DVD-Audio does not allow complex playback sequences. However, adopting the Audio Title and Group as logical structures allows the construction of large works containing multiple units of content with differing parameters, such as different encoding methods (Linear PCM or Packed PCM), sampling frequencies, bit depths, multi-channel configurations, with or without video data, etc. Up to nine Groups can be contained within a Volume, and up to 99 ATTs can be contained within each Group. However, the maximum number of ATTs per disc Volume is also limited to 99.
Group and Track numbers are the units accessible by users from their DVD-Audio players. Further, a smaller, optional access unit called an Index is also defined. An Index is a playback unit which may be comprised of one or more cells. The Index was defined primarily to specify numbers of logical units within a track. Index numbers start from 1 within each Track.
16. DVD-R and DVD-RW
Chapter 6 - DVD-R and DVD-RW
6.1 History of Specification Publications
The specification for the write-once DVD-R disc, DVD-R (3.95 GB) Book version 1.0 was released in 1997, and Pioneer began selling industrial DVD-R discs and drives that same year. A preliminary specification for a 4.7 GB disc, Book version 1.9, was released in November 1998. However, as a result of discussions about issues related to copy protection, the 4.7 GB DVD-R specification was divided into two specifications, DVD-R for Authoring version 2.0, and DVD-R for General version 2.0, which were published in February and May of 2000, respectively. Following that, supplemental information documents were published as addendums to the General specification in September and December of 2000, bringing the DVD-R specification to the form in which it exists today.
The specification for the rewritable DVD-RW disc, on the other hand, targeted a 4.7 GB capacity from the start. Version 1.0 of that specification was published in November 1999. In September of 2000 revision information was released to bring the specification to version 1.1, with a supplemental information addendum also published in September and December, bringing that specification to the form in which it exists today.
The content of those specifications will be described later in this chapter. A broad range of DVD-R discs, DVD-RW discs, DVD recorders, and DVD-R/RW drives based on these specifications are now being introduced to the market.
Figure 1 History of DVD-R/RW disc specification publications
17. DVD-R and DVD-RW - Page 2
6.2 Basic Concept
The basic concept behind DVD-R and DVD-RW are now well-known. The most fundamental concept is that these discs are compatible with read-only DVD discs. This is exactly equivalent to the relationship between CD-ROM discs, and CD-R and CD-RW discs. The basic discs are high-volume pressed versions, with compatible recordable media also playing a major role. Therefore, the 4.7 GB DVD-R disc is specified such that after recording, its signal characteristics and format of the recorded data are the same as those defined by the DVD-ROM specification. The same is true of DVD-RW; with the exception that the reflectivity of DVD-RW discs are the same as that of dual-layer DVD-ROM discs, DVD-RW discs are like DVD-R discs with the addition of rewrite capability.
Since all these specifications are defined based on this fundamental concept, DVD-R and DVD-RW discs can be easily played in players designed for read-only DVDs and in DVD-ROM drives.
Figure 2 Basic Concept
18. DVD-R and DVD-RW - Page 3
6.3 Basic Specifications
This section will describe the basic specifications that are common to 4.7 GB DVD-R and DVD-RW discs.
As explained previously, the basic playback specifications of DVD-R and DVD-RW discs after recording are the same as those for DVD-ROM discs. As shown in the table below, the reflectivity of DVD-RW discs differs from that of single-layer DVD-ROM discs (but is the same as that of dual-layer DVD-ROM discs). With that exception, other parameters such as recording capacity, density (track pitch, minimum pit length), and recorded signal playback quality follow suit with the parameters of single-layer DVD-ROM discs.
Table 1 Comparison of Basic Playback Specifications with Those of DVD-ROM Discs
||635 / 650 nm
|Objective lens NA
||45 to 85 %
||18 to 30 %
|Data track form
||Single spiral track
||DPD (Differential Phase Detection)
|Minimum pit length
||8 / 16, RLL(2,10)
||RS-PC (Reed-Solomon Product Code)
|Channel bit rate
||3.49 m/s (CLV)
|User data capacity
||4.70 Gbytes / side
As shown in Figure 3, the recording tracks (grooves) "wobble" at a fixed frequency, and address pits called Land Pre-Pits are positioned between the recording tracks. (The details of this structure will be explained later.) These two types of addressing are used during recording to control disc rotation and generate the recording clock, as well as providing information such as recording address, which is necessary in the recording process.
After recording, the disc Information Area, the playback region, has exactly the same structure as that of a DVD-ROM disc, and the data format is also exactly the same. Closer to the center of the disc than the Information Area is another region, called the R-Information Area, which is peculiar to DVD-R and DVD-RW discs. This area contains an area called the PCA (Power Calibration Area), which is used for laser power calibration, and an area called the RMA (Recording Management Area), which contains recording management information necessary for the recording device. This information is provided to prevent problems in playing these writable discs in ordinary players and drives.
Figure 3 Disc Structure Common to DVD-R and DVD-RW
6.3.1 Preformat and addressing
DVD-R and DVD-RW discs use groove wobble and land pre-pits as a means for providing pre-format. As shown in Figure 3, the disc substrate contains grooves which are used to guide the laser beam, and the data is recorded in these grooves. The areas between adjacent grooves are called lands. Groove wobbling means that the grooves wander back and forth with a fixed amplitude and spacial frequency. Land pre-pits are isolated pits formed on the lands in a fixed pattern. The major uses of these two features are as follows:
- generation of a spindle motor control signal
- generation of a gate signal used in detection of the land pre-pits
- high-precision positioning when writing data
acquisition of recording address and other information necessary for recording
The combination of these two features provides a high precision, highly reliable pre-format.
This pre-format signal is obtained through differential detection of the laser light reflected from the disc during tracking, but is designed so as not to be detected in the overall signal ordinarily used to obtain user data from an optical disc. That is, the pre-format signal used during recording is designed so that it has no effect on the playback of data the user has recorded to the grooves.
Figure 4 shows a basic diagram of the detected signal. As seen in the figure, the groove wobble signal is detected as a sine wave, while the land pre-pit signal is coincident with the first three peaks of the wobble signal in each synch frame (an odd or even frame). These three pulses make up one set. These three pits are assigned in a fixed pattern. The first bit always exists, and the sync pattern in the recorded data is synchronized with this pre-pit. This method of recording user data while providing phase compensation to the recording clock based on the pre-pit position makes it possible to append data or write data with much greater precision than is possible with CD-R and similar format.
Today, there are three types of linking loss area (the loss of user data which accompanies appending or rewriting of data), with magnitudes of 32 kB, 2 kB, and 0 bytes. Use of the above-described method makes it possible to do "lossless linking" (in DVD-R for General and DVD-RW).
Figure 4 Pre-format Detection Signals
6.3.2 Write strategy As one means of increasing recording performance when actually writing a signal to the disc, the DVD-R and DVD-RW specifications define a type of laser output multi-pulse modulation called write strategy, which rely on the fact that DVD-R and DVD-RW use heat for recording. Figure 5 shows the basic write strategy for these two types of disc. For both media types, the laser pulse for a single recording mark is divided into a top pulse and a series of multiple pulses, which provides control of distribution of heat generated in forming the mark. DVD-R uses two levels of laser power, while DVD-RW uses three levels to enable overwriting. For the latter in particular, the series of pulses is ended with a cooling pulse.
This method alleviates heat interference between adjacent and the heat accumulation at the trailing edge of the formed mark, and makes it possible to obtain a playback signal with good characteristics.
The DVD-R and DVD-RW specifications also provide the option of encoding the optimal pulse width for a particular media type and embedding that information in the land pre-pit, as a mechanism for further increasing system margin.
Figure 5 Write Strategy
19. DVD-R and DVD-RW - Page 4
6.4 Features of the Specifications
As mentioned above, the 4.7 GB DVD-R specification was divided and published as two specifications (DVD-R for Authoring version 2.0 and DVD-R for General version 2.0), out of concern for copy protection issues. The former specification is restricted to professional authoring applications, while the latter specification is available for general consumer applications. The DVD-RW specification was also designed for consumer applications, and was revised from version 1.0 to version 1.1 to perfect its copy control mechanisms. At the same time, playback compatibility with DVD-ROM was also improved.
This section will describe the commonalities and differences between these three specifications.
6.4.1 Blank disc structure
Figure 6 shows the specified characteristics of the different types of blank discs. From the figure we can see that the DVD-R for General, for consumer applications, and the DVD-RW discs have the same structure. That is, the recording laser wavelength and distribution of recording addresses included in the land pre-pit data are the same, and both require playback-only areas (areas which cannot be written) for use in preventing the recording of copy-protected data. Further, these discs contain an area near the center of the disc for (optional) NBCA copy generation management data (the details of which will be explained below).
The main difference between these and DVD-R for Authoring is in whether or not copy management mechanisms physically exist on the disc. The professional and consumer discs also use different laser wavelengths and addressing schemes so that the each types of disc is not compatible with the other style of recorder.
The means of creating a read-only region on the surface of the recording disc is currently different for DVD-R and DVD-RW. Since DVD-R for General is a write-once medium, the disc manufacturer creates the read-only area by writing to that area as part of the manufacturing process. DVD-RW, on the other hand, is a rewritable medium. In DVD-RW, the read-only area is pre-recorded with embossed pits. The quality of the signal read from the embossed pits was not specified in the DVD-RW version 1.0 specification. In revising the specification to version 1.1 it was determined that to complete the copy management mechanism that signal quality should follow suit with that of the DVD-ROM specification. As a result, the modification to the specification also helped maintain compatibility with DVD-ROM discs.
Figure 6 Structure of Blank Discs
6.4.2 Copy management technology
As described in the previous section, consumer-oriented DVD-R for General discs and DVD-RW version 1.1 discs are provided with a copy management mechanism that exists physically on the disc.
The details of the copy management mechanism are described in Figure 7.
To begin with, each DVD specification provides a mechanism for recognizing the recording media, and this is common to the entire DVD family. That is, each disc contains a flag called Book Type which indicates to which specification the disc is compliant. Recordable DVD media have a particular wobbling track, which is used as a means to recognize the recordable media. Detection of this wobbling track allows the player to reject media with an illegal Book Type; that is, media that has been recorded improperly.
Besides this, discs also are specified to have a read-only area, as has was described above, as another mechanism for preventing the recording of copy-protected information.
In DVD-R for General and DVD-RW version 1.1, by recording specified data (a Media Block Key, or MKB) to this read-only area, and by further adding a bar code style signal (called NBCA) to the disc's inner tracks, allows the disc to support a copy generation management scheme (with support for copy-once media) called Content Protection for Recordable Media, or CPRM. This additional generation management information is placed on the disc by the disc manufacturer, and is an optional feature of the specifications.
Figure 7 Copy Management Structure for the Writable DVD Specifications
DVD-R and DVD-RW are recordable and re-recordable DVD standards recognized by the DVD Forum, defined in accordance with the basic concept of providing compatibility with read-only discs.
As applications for these recordable media, the DVD Forum has established the Video Recording format, which provides excellent support for features such as video editing, and the DVD Video format (for non-copy-protected data only), which is primarily concerned with providing compatibility with the existing DVD-Video specification. These specification are available today for use in certain applications.
The DVD-R and DVD-RW specifications were promulgated somewhat later than the read-only specification, and as a result there are some compatibility issues with some of the earlier DVD players and drives. (For example, some players cannot recognize DVD-R/RW discs because the aforementioned Book Type flag is different from those of ROM discs, or because DVD-RW discs are single-layer discs but have the same reflectivity as dual-layer discs.) Recently, however, as a result of increased recognition of these specifications, standardization efforts such as RWPPI (the RW Products Promotion Initiative), and due to continuing efforts by manufacturers to improve product quality, compatibility problems and user inconveniences in the market should be considerably reduced.
Hand in hand with the increasing popularity of DVD video, audio, and ROM, we anticipate that DVD-R and DVD-RW will also quickly establish a large recordable DVD market.
Chapter 7 - DVD-RAM
7.1 Background of the DVD-RAM Specification
With the increasing performance of PCs in recent years, there has also been a dramatic increase in the quantity of data they handle. This increase is expected to continue with the increase in video usage, the move to broadband, and the increase in multimedia applications. Along with the increasing capacities of hard disks to store this data, there has also been increasing demand for high-capacity rewritable storage media. Users and computer makers have said they want a rewritable disc which is compatible with ROM discs. The rewritable disc DVD-RAM specification was created to meet these requests.
Rewritable disc technologies currently on the market include magneto-optical (MO) and phase-change. Magneto-optical discs work by using laser light and an external magnetic field to record data in changing directions of magnetic regions on the disc. Discs in use today include 130 mm and 90 mm diameter data discs, 300 mm diameter video file discs, and MiniDiscs for recording music. These discs use a signal detection method involving rotation of a polarizing plane via the magneto-optical effect.
Phase change technology, on the other hand, utilize the ability of laser light to change the recording material from a crystalline to an amorphous state, and back again. A pulse of high-power laser light heats the recording surface to above the melting point, and the material is cooled quickly to cause it to enter an amorphous state. On the other hand, an amorphous region can be heated by medium-power laser light to above the temperature for crystallization to cause it to enter a crystalline state. The signal is encoded in the difference in reflectivity due to the different optical indices of the amorphous and crystalline regions. This technology was later coming to market than magneto-optical, due to the effort required to develop sufficient rewrite durability, but 120 mm and 130 mm diameter data discs and associated hardware are available today.
Phase change technology was chosen for DVD-RAM for the following reasons.
- The use of changing reflectivity to reproduce the signal makes it easy to achieve compatibility with read-only players.
- The use of laser power modulation makes it easy to achieve direct overwrite capability.
- The optical system is simpler than the magneto-optical system required to detect rotated polarized surfaces, and there is no need for a magnetic head to apply the external magnetic field.
- A relatively large signal can be obtained even from the smaller recording marks resulting from increasing disc density, and the technology can also be made compatible with shorter wavelength blue light that is anticipated for future use.
7.2 2.6 GB DVD-RAM Specifications
||phase change disc
||120 mm diameter, bonded 0.6 mm thick substrates
|laser wavelength, NA
|ECC block size
|error correction method
||2.6 GB (one sided)
||ZCLV (Zoned Constant Linear Velocity)
|number of data area zones
||CAPA (Complimentary Allocated Pit Addressing)
|recording bit length
||mark edge recording
||0.74m, land and groove
|user data rate
Table 1 Basic Specifications of DVD-RAM version 1.0.
Table 1 shows the basic specifications of the DVD-RAM specification version 1.0. These specifications achieve the key goals of compatibility with DVD-ROM discs and a large capacity of 2.6 GB per side.
The disc dimensions are the same as for DVD-ROM, with discs 120 mm in diameter composed of bonded 0.6 mm thick substrates, and the standard pickup also has a wavelength of 650 nm and a numerical aperture of 0.6.
Further, the encoding method, sector size, ECC block size, and error correction method were specified to be 8/16 encoding, 2 kB, 32 kB, and Reed-Solomon Product Code; these are all the same as DVD-ROM, to facilitate compatibility with DVD-ROM players.
The data rate is also the same as DVD-ROM, at over 11 Mbps. The file system was also specified for compatibility with ROM, as DVD-RAM uses the Universal Disc Format (UDF) defined by the Optical Storage Technology Association (OSTA). This file system is designed to support both the random access needed for data file applications, and the sequential access needed for video recording.
21. DVD-RAM - Page 2
7.3 4.7 GB DVD-RAM Format
Table + 1 Basic Specifications of DVD-RAM version 2.0
(changes from version 1.0 highlighted with bold text)
||phase change disc
||120 mm diameter, bonded 0.6 mm thick substrates
|laser wavelength, NA
|ECC block size
|error correction method
||4.7 GB (one sided)
|number of data area zones
||CAPA (Complimentary Allocated Pit Addressing)
|recording bit length
||mark edge recording
||0.615 m, land and groove
|user data rate
After the release of the DVD-RAM version 1.0 specification, version 2.0 for 4.7 GB discs was created. The major differences between version 1.0 and version 2.0 are given below.
- 4.7 GB capacity
Version 2.0 increases the capacity of a single disc side from 2.6 GB to 4.7 GB, the same as for DVD-ROM. This was accomplished by decreasing track pitch from 0.74 m to 0.615m and recording bit length from 0.41 m/bit to 0.28 m/bit.
- 22.16 Mbps standard data rate
VThe data rate of version 1.0 is the same as DVD-ROM, at 11.08 Mbps. Version 2.0 doubles the standard data rate to 22.18 Mbps to improve data recording capability.
- Defect management method
Version 2.0 incorporates a new defect management method to support real-time recording of audio and video data.
7.4 1.46 GB (8 cm) DVD-RAM Format
Table 1 Basic Specifications of the DVD-RAM 8 cm Specification
(changes from version 2.0 12 cm specification highlighted with bold text)
||phase change disc
||80 mm diameter, bonded 0.6 mm thick substrates
|laser wavelength, NA
|ECC block size
|error correction method
||1.46 GB (one sided)
|number of data area zones
||CAPA (Complimentary Allocated Pit Addressing)
|recording bit length
||mark edge recording
||0.615 m, land and groove
|user data rate
The DVD-RAM version 2.1 specification was based on the 4.7 GB DVD-RAM version 2.0 specification to define an 8 cm disc. The major differences between the 8 cm disc and the 4.7 GB, 12 cm disc are as follows.
- 8 cm diameter
The disc size was reduced from 12 cm to 8 cm. In addition, an 8 cm case is also provided.
- 1.46 GB capacity
The recording capacity dropped from 4.7 GB to 1.46 GB as a result of the decrease in size. The track pitch is 0.615 m, and the recording bit length is 0.28 m/bit, the same as with the 4.7 GB disc.
- 14 zones
The number of zones was reduced from 41 in the 4.7 GB disc to 14.
All the remaining specifications are the same as for the 4.7 GB disc.
22. DVD-RAM - Page 3
7.5 Land and Groove Format
The figure above shows a typical DVD-RAM structure. A DVD-RAM disc holds 2.6 GB per side (5.2 GB for both sides), or 4.7 GB (9.4 GB for both sides). This high recording density was achieved through the use of mark edge recording, along with the use of land and groove recording, which is effective for use with narrow track pitches. Previous optical discs used continuous groove recording, in which data is recorded only within the tracking grooves. Land and groove recording increases recording density by writing data both in the grooves and on the lands between the grooves. There is a limit to how much track pitch can be reduced as a means of increasing recording density, as narrow track pitch tends to weaken the tracking servo signal and increase crosstalk. The solution is land and groove recording. In phase change discs the groove depth is designed to be /6n, where is the pickup laser wavelength and n is the optical index of the substrate. This reduces crosstalk between the lands and the grooves, and allows conventional tracking signal schemes to be used with narrow track pitches.
The reduction in crosstalk with the land and groove method is a result of the fact that the reduction in reflected light due to interference with a neighboring track when in crystalline state is approximately the same as decrease in reflectivity when in amorphous state at a particular depth. That depth is about /6n, which is about 70 nm for a 650 nm laser wavelength.
DVD-RAM uses this kind of land and groove recording, with a track pitch of 0.74 m (the same as in DVD-ROM) in the 2.6 GB version 1.0, and 0.615 m in the 4.7 GB version 2.0.
7.6 CAPA (Complimentary Allocated Pit Addressing)
The address signal uses a method called CAPA (Complimentary Allocated Pit Addressing) as a Physical ID (PID), and is recorded once per sector. In CAPA, the pits which record the PID are offset by one-half track from the data recording track (land or groove), to form a structure like that shown in the figure above. When groove tracking the address may be obtained from the CAPA signal behind, and when land tracking the address is obtained from the CAPA signal ahead. In each zone, the CAPA is aligned radially to allow CAV operation. The data recording area (land or groove) between each CAPA header is wobbled. Counting the number of wobbles allows the drive to accurately know the position of the next CAPA header.
23. DVD-RAM - Page 4
Sectors are comprised of CAPA headers, where the address is recorded using embossed pits, and a data recording area on a land or in a groove. The data recording area has a structure as shown in the figure above. Reading is performed by extracting the clock in the VFO area and determining a binary slice level. The PS field allows detection of the start point, and data is read. This data area contains one DVD-ROM sector of data. The buffer areas ahead and behind are there to prevent influence on data reading due to degradation of the recording layer. Further, to help prevent surface degradation, the recording position is moved about at random, to prevent degradation of the recording layer at any particular point.
Sixteen sectors of data make up one ECC block, with error correction performed on the entire block.
7.8 ZCLV (Zoned Constant Linear Velocity) Format
Figure 1 2.6 GB DVD-RAM Zone Structure
(The structures of 4.7 GB and 1.46 GB, 8 cm discs are essentially the same, with the exception of the number of zones.)
The ZCLV (Zoned Constant Linear Velocity) method divides the disc into regions with different numbers of sectors, based on radial distance. This method provides for recording at a constant data rate via zone-based rotational control, and provides high recording density and easy rotational control and signal processing.
A version 1.0 2.6 GB disc is divided into 24 zones, with 17 sectors per rotation in the innermost zone, and 41 sectors per rotation in the outermost zone.
As shown in Figure 1, a DVD-RAM is divided into a lead-in area, a data area, and a lead-out area. The lead-in area is divided into an embossed pit area and a rewritable area. The embossed pit area contains control data such as the disc type, format, and recording method. The rewritable portion of the lead-in area use used for disc or drive testing, data for processing defects in a disc, etc.