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ABSTRACT
The MiniDisc system was designed with the obvious objective of replacing the conventional Compact Cassette tape recorder system. The quick random access of Compact Disc players has become a necessity for music lovers. The high quality of digital sound is now the norm. The future of personal audio, meet the above criteria and more. Thatâ„¢s why a MiniDisc was created which was a revolutionary evolution in the field of digital audio based on an advanced miniature optical disc. The MD offers consumers quick random access, durability and high sound quality of optical media, as well as superb compactness, shock resistant portability, and recordability. In short, the MD format has been created to meet the needs of personal music entertainment in the future. Based on a dazzling array of new technologies, the MiniDisc offers a new lifestyle in personal audio enjoyment. Furthermore, MiniDisc was evolved into the MD Data system and with a data capacity of 140 Mbytes and a very compact size, the MD Data system is expected to become one of the standards for removable data storage systems
INTRODUCTION
The MiniDisc system was introduced in the consumer audio market as a new digital audio playback and recording system. The introduction time was just ten years after the introduction of the Compact Disc (CD). As is known, CD has effectively replaced the vinyl LP records in the audio disc market. CD technology is based on 16-bit quantization and 44.1-kHz sampled digital audio recording. The CD sound quality was fairly improved compared to any consumer analog recording equipment.
Before starting the CD business, many engineers engaged in the development of the CD solely for its improvement in sound quality, but after the introduction of the CD player into the market, we found out that the consumer became aware of the quick random-access characteristic of the optical disc system. The next target of development was obviously to be the rewritable CD. Two different recordable CD systems were established. One is the write-once CD named CD-R and the other is the re-writable CD named CD-MO.
Sales of cassette tapes had been decreasing since 1989. Even if recordable CD were to be accepted by the consumer, it would still be difficult to break into the portable market. Here, portable compact cassette dominated because of its strong resistance to vibration and its compactness. Clear targets for a new disc system were to overcome these weaknesses. Sony was able to achieve this by introducing a disc system called MiniDisc (MD).
The name, MiniDisc (MD), comes from its size. MiniDisc was developed by as an audio media that combines the merits of both CD (supreme quality) and Tape (recordable). The disc, with a diameter of 64 mm and thickness of only 1.2 mm, is placed inside a cartridge of 72 X 68 X 5 mm. The cartridge protects the disc from exposures and withstand forces eliminating problems that connects with CD (scratches) or tape (tangles). The Minidisc is based on Magneto-Optical technology, which is essentially a method of recording information by using a laser to alter magnetic information on the disc. In order to alter the information, the disc has to be heated to a high temperature, meaning that if left on a desk near a magnet, it should remain unaffected, unless you heat the disc to the required 180°C.

THE MINIDISC SYSTEM
TYPES OF MINIDISCS
Premastered MiniDiscs are used most commonly for music and are sold in record stores just the same as compact cassettes and CDs are. Minidiscs, just like CDs, are manufactured in large volumes by high-speed injection molders, and the music signals are recorded during replication in the form of pits. Moreover, the discs are encased in a cartridge, so there is no worry about their being scratched. The design of the premastered Minidisc cartridges is special. Prerecorded music packages require a label, featuring the artistâ„¢s picture or other information. Therefore the top face of the cartridge is left completely free for the label. A window for the laser beam to read the disc is only necessary on the bottom face. Both a CD and a Minidisc can store the same amount of music. The difference is that a Minidisc uses a digital compression technique called ATRAC (Adaptive Transform Acoustic Coding) to compress audio data in 1:5 ratio by eliminating inaudible frequencies and faint background noises.
Recordable MiniDiscs, uses Magneto-optical (MO) technology forms the heart of the recordable Minidisc technology. Not only are MO discs durable enough to withstand being rerecorded about 1 million times, they also have a life expectancy approaching that of CDs. As shown in Fig. 2, the lead-in area is on the inner circumference of the disc, followed in this case by the user table of contents area, the program area, and the disc's lead-out area on the outer circumference. Since a magnetic recording head and laser are used on opposite sides of the disc (more on this shortly), the shutter must open on both sides of the caddy (Fig. 3). The recordable MiniDisc's unique layer structure, along with the pre-groove configuration, is represented conceptually in Fig. 4. This MO layer construction has been engineered to enable Magnetic Field Modulation overwriting. According to Sony, it has already been proven to handle more than one million over recordings without degradation and to provide excellent long-term storage characteristics. It seems unlikely that anyone would erase and record a MiniDisc so many times!
Hybrid MiniDiscs has both recorded pits and a recordable wide-groove sputtered magneto-optical recording layer. The wide groove is wobbled by a 22.05-kHz carrier modulated by address data. This type of pre-groove modulation helps the drive system to control not only the tracking servo but also supports the constant linear velocity (CLV) control and access control during record mode.
It is mandatory for the MD system to be able to play back these three types of discs. This means that the MD recorder/player is equipped with a dual-function optical pick-up for the read-out of recorded pit patterns and the magneto-optical disc.

The given figure shows the 3 types of Minidiscs with their groove/pit layout.

MINIDISC PICK-UP TECHNOLOGY
The optical pick-up developed for the MD system has the remarkable ability to read both recordable and premastered Minidiscs. For recordable discs, the pick-up detects the magnetic structure along the track. For premastered optical discs, it detects the geometric structure along the track. The MD system is based on the design of the standard CD pick-up with the addition of a MO signal readout analyzer and two photodiodes. During playback of recordable discs a 0.5mW laser is focused onto the magnetic layer. The magnetic signal on the disc affects the polarization of the reflected beam. The direction of polarization is converted into light intensity by the MO signal readout analyzer. Depending on the direction of polarization one of the two photodiodes are subtracted and depending on whether the difference is positive or negative, a 1 or 0 signal is read.
The same 0.5mW laser is used for the playback of premastered optical discs. The amount of light reflected depends on whether or not a pit exists on the surface of the disc. If there is no pit, a high proportion of the light is reflected back through the beam splitter and analyzer into the photodiodes. If a pit does not exist, some of the light is diffracted and less light reaches the photodiodes. The electrical signals from the photodiodes are added up in this case and depending on the sum, a 1 or 0 is read.


OVERWRITE TECHNOLOGY
In order to meet the requirements of a compact, lightweight, recordable audio system for personal use, the MD system employs a newly developed magneto-optical (MO) disc that utilizes magnetic field modulation with direct overwrite capability. With MO disc technology, the recording of data requires the use of a laser and polarizing magnetic field. When the magnetic layer in the disc is heated by the laser to a temperature above the Curie point (approximately 200°C), it is temporarily looses its coercive force. As the disc rotates and the irradiated domain returns to normal temperature, its magnetic orientation is determined by an externally applied magnetic field. Polarities of N and S can thus be recorded, corresponding to digital data 1 and 0.
The MD overwrite system positions a magnetic head directly across from the laser source on the opposite side of the disc. A magnetic field corresponding to the input signal is generated over the laser spot. The rotation of the disc then displaces the area to be recorded, allowing the temperature at the spot to drop back below the Curie point. At that point, the domain takes on the polarity of the applied magnetic field regardless of the polarity that previously existed.

QUICK RANDOM ACCESS
The ease of quick random access was made possible by the development of the Compact Disc (CD). The CD instantaneously provides random access to the beginning of any desired music selection. After using a CD player, the time to reach the music selection of your choice with cassette tape players seems extremely cumbersome.
The MiniDisc provides the same high-speed random access for recordable discs as well as for premastered discs. In addition, the recordable MiniDisc has a circumferential microgroove or pre-groove , which is formed when the polycarbonate substrate is injection molded. This pre-groove is the basis for the tracking servo and spindle servo operation during recording or playback. Address information is recorded at intervals of 13.3 milliseconds using a technology that places infinitesimal zigzags on this pre-groove. Therefore, the disc has all the addresses already notched along the groove even with no recording. The result is a stable and quick random access, as well as a variety of optional features, including programming of the playback sequence e.g.: rearranging the sequence of the titles recorded on the MD without rerecording of the music information in a matter of seconds.
The starting and ending addresses for all music tracks recorded on the disc are stored in this area, enabling easy programming just by rewriting the addresses. This supports also other features: it is possible to erase a track out of sequence and during playback no gap in the remaining music will be heard. The erased segment is allocated to the free space “ it is possible to record a piece of music independent of the number of segments used.
ATRAC Digital Audio Compression Technology
ATRAC is the name given to the compression system used on a Minidisc and is an abbreviation for Adaptive Transform Acoustic Coding. Because Minidiscs only hold one fifth of the information that a compact disc does, the compression is needed so that a full 74 minutes of music can be recorded without sacrificing much in the way of sound quality. If compression wasnâ„¢t used the maximum amount of music we would be able to store at CD quality, would be just under 15 minutes. Despite only one fifth of the information being stored on a minidisc, the difference in the sound quality is amazingly small, and this is all down to the clever strategies involved in the ATRAC system. ATRAC is a perceptual coding method, which omits data deemed inaudible due to masking. For example, if an audio signal has two sounds that are about the same frequency, and one sound is louder than the order, the quieter sound will be inaudible due to masking. So ATRAC removes the quieter sound, which would be inaudible anyway.
ATRAC has had several revision levels; the latest version is 4.5. The higher the version number, the better the sound. Some reviewers have claimed that version 4.5 sounds essentially the same as compact discs when playing a musical program. Earlier versions are said to be near-CD in quality, and much better than MP3. All versions are compatible. Sound quality depends not only on the ATRAC version, but also on the quality and bit depth of the A/D converter in the recorder. There is a slight generation loss when tracks are copied or bounced. The signal is ATRAC-processed with each copy. After more than five copies or so, the sound cumulatively begins to take on a mid-to-low rumble and a high-frequency squeak. Minidisc recorders can make ATRAC-compressed copies of CDs directly from the CD playerâ„¢s digital output.
In 16-bit encoding, currently used in the CD and DAT formats, with a sampling frequency of 44.1kHz, the analog signal is sampled approximately once every 0.02 milliseconds. Each sample is quantized at 16-bit resolution into one of 65,5536 possible values. Therefore, with CD and DAT, when the analog signal is converted to digital data in real time, 16 bits of data are used every 0.02 milliseconds, regardless of the amplitude of the signal and whether or not a signal is present at all.
The ATRAC encoding process starts with the 16-bit quantization and 44.1-kHz and analyzes segments of the data for waveform content every 11.6msec. The key to ATRAC's efficiency is its unique method of analysis. ATRAC employs a non-uniform slitting in both frequency and time axes, reflecting psychoacoustic principles. Block diagram of an ATRAC encoder is given in Fig 5.

The encoding processes are divided into three steps. First is the Quadrature Mirror Filters (QMF's) block. Second, the Modified Discrete Cosine Transform (MDCT) block. Third, there is a Bit Allocation block. First, the signal is divided into three subbands by using two stages of QMF filters. Each band covers 0-5.5 kHz, 5.5-11 kHz, or 11-22 kHz. After that, each of the three subbands is transformed into the frequency domain by using the MDCT.
The transform block size is adaptively chosen. There are two modes, long mode: 11.6 ms for all frequency bands and short mode: 1.45 ms for the high-frequency band and 2.9 ms for mid- and low-frequency bands. Normally, the long mode is chosen to provide optimum frequency resolution. However, problems may occur during attack portions of the signal. Specifically, the quantization noise is spread over the entire MDCT block time. Just before the attack of the sound, one may hear some noise. Therefore, ATRAC automatically switches to the short mode to avoid this type of noise.
The MDCT spectral coefficients are the grouped into a Block. The spectral values are quantized by using two parameters. One is word length, another is scale factor. The scale factor defines the full-scale range of the quantization and the word length defines the resolution of the scale. Each Block Floating Unit (BFU) has the same word length and scale factor, reflecting the psychoacoustic similarity of the grouped frequencies. The scale factor is chosen from a fixed table and reflects the magnitude of the spectral coefficients in each BFU. The word length is determined by the bit allocation algorithm. For each sound frame (512 data samples) the following information is stored on disc:
MDCT block size mode (long or short),
word length data for each BFU,
scale factor code for each BFU,
quantized spectral coefficients.
The data size of each sound frame is fixed as 212 bytes. On the disc, 11 stereo sound frames are recorded every 2 sectors. In case of monaural recording, twice the amount of time can be recorded on the disc.
The bit allocation algorithm divides the available data bits between the various BFU's. ATRAC does not specify a bit allocation algorithm. The word length of each BFU is stored on the MiniDisc along with the quantized spectra, so that the decoder is independent from the allocation algorithm. This allows for an evolutionary improvement of the encoder without changing the MiniDisc format. The decoding process is divided into two steps. The decoder first reconstructs the MDCT spectral coefficients from the quantized values, by using the word length and scale factor parameters. The coefficients are transformed back into the time domain by inverse MDCT using either the long mode or the short mode as specified in the parameters. Finally, the three time-domain signals are synthesized into the output signal by QMF synthesis filters.
THE ATRAC DECODER
A block diagram of the decoder structure is shown below. The decoder first reconstructs the MDCT spectral coefficients from the quantized values, using the word length and scale factor parameters. These spectral coefficients are then used to reconstruct the original audio signal. The coefficients are first transformed back into the time domain by the inverse MDCT (IMDCT) using either long mode or short mode as specified in the parameters. Finally, the three time-domain signals are synthesized into the output signal by QMF synthesis filters.

Parameters
Quantized Output
Spectra Straight PCM
SHOCK-RESISTANT MEMORY
Conventional optical pick-up systems can easily mistrack when subjected to shock or vibration. In digital audio CDs, this causes skipping or muting. In the MD system, this problem can be solved with a unique shock-resistant memory. While the MD pick-up can read information off the disc at a rate of 1.4Mbit per second, the ATRAC decoder requires a data rate of only 0.3Mbit per second for real time playback. This difference in processing speed enables the use of a readahead buffer, placed between the pick-up and the decoder. If a 4Mbit memory chip is used for the buffer, it can store up to 10 seconds of digital information. Should the pick-up be jarred out of position, the correct information continues to be supplied to the ATRAC decoder from the buffer memory. As long as the pick-up returns to the correct position within 10 seconds, the listener never experiences mistracking or muting. Since signals enter the buffer memory faster than they leave it, the buffer will eventually become full. At that point, the MD player momentarily stops reading information from the disc, it resumes reading as soon as there is again room in the memory chip.
Using a concept called sector repositioning, the MD pick-up has the ability to quickly resume reading from the correct point after being displaced. When signals are recorded on the MiniDisc (either recordable MO or premastered optical media), address information is assigned every 13.3 milliseconds. When a pick-up is shifted out of place, the MD player quickly recognizes the disruption, identifies the wrong address, and instantly returns the pick-up to the correct position.


NetMD
NetMD is an extension to the Minidisc format that allows direct transfers of compressed, ATRAC audio from a PC to Minidisc via USB interface. Audio transfers can be conducted at rates considerably faster than realtime (up to 64x for LP4 audio on certain units). It was announced in mid-2001 and first introduced on the Sony MZ-N1 portable recorder in December. NetMD equipment requires complementary NetMD PC software for control and data transfers functions to be conducted. By standardizing PC<->MD USB protocol, Sony assures compatability between NetMD equipment and NetMD software packages from various manufactures. Net MD technology adds utility to the world's most popular digital music recorders by providing up to 32x speed for transferring music files. The new QuickRip CD dubbing application facilitates fast transfer of CDs to MD without storing files on a hard drive. Users simply launch the application and select the tracks they want to transfer to the player.
Three recording modes give users the choice to record in standard mode for the richest sound quality or two different long play modes for the most effective use of space on a single MD. The bundled Open MG„ jukebox management software supports secure music downloads and is used to organize playlists, title tracks and maximize music mixes. As with all MD products, Sony's new Net MD players can record from various sources, accept multiple Internet audio formats such as MP3 and WMA files, and feature flexible editing tools. MiniDisc media is affordable, durable and re-recordable up to a million times without degradation. Net MD technology was created in response to consumer demand for high-speed digital recording on MiniDisc. MD has been widely accepted because of its ability to record over five hours of music from almost any source all on one $2 disc. By adding high-speed transfer, Sony has improved upon the number one selling digital music recorder - MiniDisc with PCLink.
MINIDISC LONG PLAY (MDLP)
One of the latest developments in MD technology is called MDLP (minidisc long-play). MDLP enabled units allow the user to lower the sampling rate or bits per second of the audio, which in turn lowers the quality of the audio, but increases the amount you can store on a single disc. Recorders with MDLP mode can use ATRAC3 compression to fit more material onto a single MD.
It is a new encoding method for audio on Minidisc that offers two modes: one gives 160 minutes stereo (LP2), the second gives 320 minutes stereo (LP4). LP2 is stereo encoded (each channel is independent), LP4 is joint-stereo (both channels are coded simultaneously). However, MDLP recordings will not play back on non-MDLP-capable players. Since ATRAC3 uses more compression than ATRAC, the sound quality of MDLP recordings is slightly lower than that of standard ATRAC recordings, and LP2 recordings sound better than LP4. Non-MDLP-capable players cannot play back MDLP (ATRAC3) recordings.
SERIAL COPY MANAGEMENT SYSTEM (SCMS)
The MD conforms to the SCMS convention. The Serial Copy Management System allows to make a first digital copy from digital sources. Further digital copies from protected sources are prevented, copies in the analog domain remain possible.
The premastered MD has following additional advantages:
The data is stored in physical pits and is therefore never erased unless it is mechanically destroyed.
The label area is larger than the one of the recordable MD. The entire area of one side can be used for labeling. The recordable MD has a shutter on both sides and its label is relatively small.
The premastered MD contains valuable character information (e.g. disc & track names) which will not be transferred during copying.
The subdata capacity of the premastered MD is bigger. So it is possible to record more character information onto the MD.

ADDITIONAL TOC DATA
As one of the new features of the MD, character information can be displayed during playback. This information is included in the TOC (table of contents) area of the MD and in subdata areas (future use) which are available in addition to the music data. This allows to store data like disc title, track name, disc recording date and track recording date in the TOC. For disc title and track names in total up to 2048 characters are available. This text information can be recalled during play back of the MD and then displayed on the character display of the MD player. It is recommended to use this feature for UPC/EAN Code, ISRC Code, disc and track names. All TOC data has to be supplied together with the other production components.
FEATURES OF MINIDISC
QUICK RANDOM ACCESS
The Minidisc offers quick random access to the music selection or phrase of your choice; something only a disc is capable of.
TOTAL DURABILITY
The minidisk can never stretch, break or tangle like cassette tapes. Since the free floating optical pick-up never touches the surface, scratches are impossible.
SUPERB COMPACTNESS
The Minidisc itself is only approximately 64mm in diameter, and the cartridge is 72*68*5 mm. And because the Minidisc is smaller, and so is the Minidisc player.
SHOCK RESISTANT PORTABILITY
The Minidisc is resistant against shocks and vibrations. New technology, using an advanced semiconductor memory, provides almost total shock resistance.
EASY TO HANDLE
The disc is protected in a cartridge. It is easy to handle and ideal sound carrier for mobile use.
UNSURPASSED DIGITAL SOUND
The Minidisc is based on the same noiseless and distortion-free digital recording technology as the compact disc, and has CD sound quality. Minidisc utilizes ATRAC compression technology, which will recreate better and more distinctive sounds than normal CD.
RECORDABLE DISC
4 Track Recording: The Minidisc offers about 74 minutes digital recording on one tiny disc.
FEATURES OF THE NEW GENERATION MINIDISC
ATRAC-R DSP
The very latest generation of the original ATRAC system which uses data reduction (not audio compression) to cram up to 80 minutes of near CD quality digital audio onto a compact, robust carrier (the MD). The type R DSP makes recordings virtually indistinguishable from the original, and allows new functions such as Scale Factor editing (qz.).
RAM EDIT
The RAM edit function allows the user to make changes to the information on a disc, without actually changing the disc's Table of Contents until absolutely convinced the changes are correct. Provides a sophisticated UNDO function, basically. Also allows temporary editing of read only or pre-recorded discs.
SCALE FACTOR EDIT
Writes information onto the disc regarding the playback level, so adjustments (± 12dB) can be made to the record level in 2dB steps AFTER the original recording has been made, and will play back on any MD machine. Fade In & Fade outs are also made possible. This is most useful when making small changes to levels, and allows some degree of failsafe operation - recordings can be made at a conservative level (with say 6dB of extra headroom) and then adjusted afterwards. It also allows multiple tracks to be "remastered" to be at the same output level.
Note that the scale factor edit operation actually alters the data on the disc directly, so that large increases or decreases in level may result in irreversible clipping or dynamic range reduction.
PRODUCTION AND PROCESS OF
PREMASTERED MD
MD PRODUCTION

1. INPUT MATERIAL
The following input components are required:
A MD master tape or a sound carrier as for CD production (e.g. PQ-encoded U-matic 1630).
Printed films, as well as color proofs, for artwork, label-and cartridge print.
Production can be started as soon as all necessary components have arrived.
2. PREMASTERING
At the premastering studio the CD-Master tape is converted to a MD-Master tape. This means that the audio information is compressed by a Format Converter using the ATRAC compression technology. Also the PQ-code is converted to MD specific data and optional sub data can be added. All information then is recorded onto a MD Master.
3. MASTERING
A nickel stamper for MD replication is produced in the same process as for CD. A glass plate is coated with a thin layer of photo lacquer. A laser spot records the data from the MD Master into the photo lacquer. The nickel negatives which are produced from the developed plate are used to replicate the MD.
4. DISC REPLICATION
The replication process of the MD is the same as for CD. After creating a disc by using high precision molding technology, the MD is coated with a thin layer of aluminum as reflective media, and subsequently with protective lacquer to protect it against damage. Then the coated discs are 100% quality inspected.
5. CARTRIDGE ASSEMBLY
As the first step in the finishing process, the cartridge is prepared with a paper label glued onto the front and other information printed in white on the back and spine. After the clamping plate has been mounted onto the MD, the MD is set into the cartridge halves and the cartridge is welded.
6. PACKAGING
Packaging is done very similar to CD packaging, with a booklet and a backline card added to the MD in a special MD jewel case.

MINIDISC SYSTEM SPECIFICATIONS
CHANNELS 2(STEREO)
FREQUENCY RESPONSE 5 “ 20,000 Hz
DYNAMIC RANGE 105 dB
WOW “ AND FLUTTER UNMEASURABLE
SAMPLING FREQUENCY 44.1 kHz
CODING SYSTEM ATRAC SYSTEM
MODULATION SYSTEM EFM
ERROR CORRECTION SYSTEM CIRC
DISC SPEED 1.2 “ 1.4 m/sec (CLV)
RECORD/PLAYBACK TIME ABOUT 74 MINUTES
CARTRIDGE SIZE 72 * 68 * 5 mm
DISC DIAMETER 64 mm
MD COMPONENTS
The MD consists of the following components:


UPPER CARTRIDGE (e.g. Polycarbonate)
LABEL (Paper)
DISC (e.g. Polycarbonate)




MD Jewel Case (

1. UPPER CARTRIDGE
The upper cartridge is made of grey plastics (e.g. polycarbonate). Its purpose is to protect the MD against mechanical damage or dust. The upper cartridge also forms the spine on which the disc ID information will be printed in white ink.
2. LABEL
The paper label is glued onto the upper cartridge.
3. DISC
The disc is manufactured in the same way as CDs are. It has a polycarbonate layer which contains the data. A thin layer of aluminum is used as reflective media, which is protected by a protective layer against destruction.
4. CLAMPING PLATE
The clamping plate is made of magnetic stainless steel. This steel plate allows to stabilize the MD from the bottom side with a magnetic chuck. Therefore the MD does not require a hole in the upper cartridge and so almost the complete surface of the upper cartridge can be used for the label.
5. SHUTTER LOCK
It is made of plastics (e.g. POM) and locks the shutter in the close position.
6. SHUTTER
The shutter is made of plastics (e.g. POM). It closes the opening in the lower cartridge through which the data is read and it protects the MD against dust and damage.
7. LOWER CARTRIDGE
Also the lower cartridge is made of grey plastics (e.g. Polycarbonate). It contains openings for the disc-drive and the laser that reads out the data. On the backside, information like artist, titles, playing time, etc as well as the catalogue number is printed directly on the cartridge in white ink.


8. MD JEWEL CASE
The MD is packaged in a 3-piece Jewel Case, consisting of clear bottom and lid parts and a gray tray. It contains a booklet and a backline card similar as CD package. The MD jewel case dimensions are 110*91*15 mm.

Fig. 6 DISC

AUDIO FORMAT COMPARISON TABLE
Format General Summary Drawbacks
CD Developed for professional and
consumer use. No data compression.
easily reproduced at low cost thus
used by the majority.
Sampling Rate: 44.1 kHz
Frequency Range: 20 Hz “20 kHz Low endurance (highly
scratchable); Cannot be
personalized; Re-record
ability limited to CD-R/W;
vulnerable to shocks and
vibration (CD players).
MD Developed for high end and professional
use with easy re-recording abilities.
compresses audio data in 1:5 ratio using
ATRAC technology to retain near
original sound quality. Easily reproduced
at low cost and able to record from all
sources. Highly portable and personalize.
Sampling rate: 44.1 kHz
Frequency range: 20 “2- kHz Not popular enough
outside of Asia; Hard to
get equipments and
accessories (outside of
Asia).
MP3 Developed for massive reproduction
through computers. Compresses audio
data in 1:10 ratio and may sacrifice
sound quality. Easily reproduced and
distributed through computers (and only
through computers).
Sampling rate: 44.1 kHz
Frequency range: 20 “20 kHz All editing operations have
to be done through
computers. Cannot be
personalized; Sound
quality is not standardize
Tape Developed as a recordable medium for
massive reproduction at low cost by
sacrificing sound quality. No data
compression. Its era was between 1980
to mid 1990 and should now officially
retire.
Sampling rate: 22 kHz
Frequency range: 30 “15 kHz Cumbersome cassette
Format; Low endurance;
Bad sound quality.

DAT Developed for high end and professional
use. No data compression. High capacity
of up to 124 min.
Sampling rate: 48 kHz
Frequency range: 20 “ 20 kHz Cumbersome cassette
format.
FUTURE OF MINIDISCS
MiniDiscs appeared to particularly well suited for portable applications (beside being small, it is inherently resistant to shock during playback) and is more flexible than CD-Rs/CD-RWs in terms of editing. In addition to being able to record up to 255 tracks (compared with 99 on a CD), the user can delete, combine, move, and divide tracks after they have been recorded. MDs also enable the user to label recordings with disc and song titles, artists' names, etc., for display during playback.
On the other hand, MDs fall far short of CDs in terms of marketplace penetration. Few prerecorded titles are available, and--because the format is not compatible with CDs and the number of people owning machines remains small--the opportunities for using them are severely limited.
Damned by audiophiles (who regard its compression system as an inferior form of digital storage) and little known by educators (who rarely seem to be in the vanguard of AV technology), the format has remained marginal since its inception. As the price of recordable CD equipment and blank discs continues to drop (as of 1998, both are already much cheaper than competing MD hardware and software), the future for MDs appears to be in considerable jeopardy.


CONCLUSION
The quick random access of Compact Disc players has become a necessity for music lovers. The high quality of digital sound is now the norm. The future of personal audio must meet the above criteria and more. Thatâ„¢s why Sony has created the MiniDisc, a revolutionary evolution in the field of digital audio based on an advanced miniature optical disc. Introduced by Sony, the MiniDisc (MD) is an erasable, laser-optical format that employs a 2.5-inch disc housed in a protective caddy resembling a 3.5-inch computer diskette.
MiniDisc Technology is truly an audio revolution with the merits of high quality sound, versatile recording options, and MP3 friendly features. Considering the many advantages of the disc media, we can expect that MiniDisc will replace the Compact Cassette in the near future. When this occurs, we are certain that the MiniDisc player unit will be smaller than the current Walkman Compact Cassette player, largely due to the MD's cartridge size. In order to realize this, the key issue is to downsize the relatively bulky electronics into silicon. The key issue here is the huge number of gates and the total number of LSI chips and this will soon be overcome by the progress in LSI design rules. At that time we can also expect broad application of the MD-Data format.

REFERENCES
1. minidisc.org
2. minidisco.org
3. dadc_minidisc.org
4. t_stationmd_comparison.html
5. t_stationmd_facts.html
6. t_stationmd_tech.html
7. users.skynet.be
8. news.sel.sony.com
9. minidisc.org.MetMD.html
10. totalaudio.co.uk
11. minidiscmdlpfaq.html
12. aes.org
13. minidiscussion.com
14. tape.com
15. minidisccharman

CONTENTS
Page
1. Introduction : 1
2. Types of MiniDiscs : 2
3. MiniDisc Pick-Up Technology : 4
4. Overwrite Technology : 5
5. Quick Random Access : 6
6. ATRAC Digital Audio Compression Technology : 7
7. The ATRAC Decoder : 10
8. Shock Resistant Memory : 11
9. NetMD : 12
10. MiniDisc Long Play : 13
11. Serial Copy Management System (SCMS) : 14
12. Additional TOC Data : 14
13. Features of MiniDisc : 15
14. Features of New Generation MiniDisc : 16
15. Production and process of Premastered MD : 17
16. MiniDisc System Specification : 19
17. MiniDisc Components : 20
18. Audio Format Comparison Table : 23
19. Future of MiniDisc : 24
20. Conclusion : 25
21. References : 26

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