Definition

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.

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 artist'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.

MiniDisc (MD) is a magneto-optical disc-based data storage device initially intended for storage of up to 80 minutes of digitized audio. Today, in the form of Hi-MD, it has developed into a general-purpose storage medium in addition to greatly expanding its audio roots. MiniDisc was announced by Sony in 1991 and introduced January 12, 1992. The music format was originally based exclusively on ATRAC audio data compression, but the option of linear PCM recording was ultimately introduced to attain CD-quality recordings. MiniDiscs were popular in Japan and Asia as a digital upgrade from cassette tapes, but were not as popular elsewhere the disc is permanently housed in a cartridge (68 × 72 × 5 mm) with a sliding door, similar to the casing of a 3.5" floppy disk. This shutter is opened automatically by a mechanism upon insertion. The audio discs can either be recordable (blank) or pre mastered. Recordable MiniDiscs use a magneto-optical system to record data. A laser heats one side of the disc to its Curie point, making the material in the disc susceptible to a magnetic field. A magnetic head on the other side of the disc alters the polarity of the heated area, recording the digital data onto the disk. Playback is accomplished with the laser alone: taking advantage of the Faraday effect, the player senses the polarization of the reflected light and thus interprets a 1 or a 0. Recordable MDs can be recorded on repeatedly; Sony claims up to one million times. As of May 2005, there are 74 minute and 80 minute discs available. 60 minute blanks, which were widely-available in the early years of the format's introduction, were phased-out long ago and are rarely seen. Pre mastered MiniDiscs use a mastering process and optical playback system that is very similar to CDs, making them physically dissimilar to recordable discs. The recorded signal of the pre mastered pits and of the recordable MD are very similar to that of the CD. Eight-to-Fourteen Modulation (EFM) and a modification of CD's CIRC code, called Advanced Cross Interleaved Reed-Solomon Code (ACIRC) are employed. Differences from cassette and CDs MiniDiscs use rewritable magneto-optical storage to store the data. Unlike the Digital Compact Cassette, or the analog compact audio cassette, the disc is a random-access medium, making seek time very fast. MiniDiscs can be edited very quickly even on portable machines. Tracks can be split, combined, moved or deleted with ease either on the player or uploaded to PC (only with the latest version of Sony's PC based Sonic Stage V4.3 software) and edited there. Transferring data from an MD unit to a non-Windows machine can only be done in real time, preferably via optical I/O, by connecting the audio out port of the MD to an available audio in port of the computer. With the release of the Hi-MD format, Sony began to release Macintosh compatible software. However, the Mac compatible software is still not compatible with legacy MD formats (SP, LP2, LP4 ) This means that using an MD recorded on a legacy unit or in a legacy format still requires a Windows machine for non-real time transfers. At the beginning of the disc there is a table of contents (TOC, also known as "System File" area of the disc), which stores the start positions of the various tracks, as well as meta information (Title, Artist) about them and free blocks. Unlike the conventional cassette, a recorded song does not need to be stored as one piece on the disk, it can be stored in several fragments, similar to a hard drive. Early MiniDisc equipment had a fragment granularity of 4 seconds audio. Fragments smaller than the granularity are not kept track of which may lead to the usable capacity of a disc actually shrinking. Also, no means of de fragmenting the disc are provided in consumer grade equipment. All consumer-grade MiniDisc devices feature a copy-protection scheme known as Serial Copy Management System. An unprotected disc or song can be copied without limit, but the copies can no longer be digitally copied. However as a concession to this the most recent Hi-MD players can upload to PC a Digitally Recorded file which can subsequently be resaved as a WAV (PCM) file and thus replicated. Audio data compression MD Walkman The digitally encoded audio signal on a MiniDisc has traditionally been data-compressed using the ATRAC format (Adaptive Transform Acoustic Coding). ATRAC was devised for MiniDisc so that the same amount of audio a CD can carry can fit on a disc far smaller than the CD (which contains uncompressed 16-bit stereo linear PCM audio). ATRAC was also used on nearly all Walkman devices until the 8 series but is now only used in Sony's MiniDisc devices (as of November 2008) as ATRAC are fundamental to the MiniDisc specification. In MiniDisc's latest progression, Hi-MD, uncompressed CD-quality linear PCM audio recording and playback is offered in addition to ATRAC compression of varying bit rates; placing Hi-MD on par with uncompressed, CD-quality audio for the first time. Sony's ATRAC codec differs from uncompressed PCM in that it is a psychoacoustic loss audio data compression scheme, so decompression of the compressed signal will not yield the original signal, although the compressed signal may sound identical to the original to the listener. The latest version of Sony's ATRAC is ATRAC3plus. Original ATRAC3 at 132 kbit/s (also known as ATRAC-LP mode) is the format used by Sony's Connect audio download store. ATRAC3plus is not used in order to retain backwards compatibility with earlier NetMD players. Anti-skip MiniDisc has a feature that prevents disc skipping under all but the most extreme conditions. Older CD players had once been a source of annoyance to users as they were prone to mistracking from vibration and shock. MiniDisc solved this problem by reading the data into a memory buffer at a higher speed than was required before being read out to the digital-to-analog converter at the standard rate required by the format. The size of the buffer varies by model. If the MiniDisc player were bumped, playback could continue unimpeded while the laser repositioned itself to continue reading data from the disc. This feature allows the player to stop the spindle motor for long periods, increasing battery life. The memory buffer concept introduced by MiniDisc was soon incorporated into portable CD players as well, and in hard drive based digital audio players. A buffer of at least six seconds is required on all MiniDisc players, be they portable or stationary, full-sized units. This is needed to ensure uninterrupted playback in the presence of fragmentation. Operation MiniDisc Deck MDS-JE780 The data structure and operation of a MiniDisc is similar to that of a computer's hard disk drive. The bulk of the disc contains data pertaining to the music itself, and a small section contains the Table of Contents (TOC), providing the playback device with vital information about the number and location of tracks on the disc. Tracks and discs can be named. Tracks may easily be added, erased, combined and divided, and their preferred order of playback modified. Erased tracks are not actually erased at the time, but are marked so. When a disc becomes full, the recorder can simply slot track data into sections where erased tracks reside. This can lead to some fragmentation but unless many erasures and replacements are performed, the only likely problem is excessive searching, reducing battery life. The data structure of the MiniDisc, where music is recorded in a single stream of bytes while the TOC contains pointers to track positions, allows for gapless playback of music, something which the majority of competing portable players, including most MP3 players, fail to implement properly. (Notable exceptions are CD players, as well as all recent iPods.) At the end of recording, after the "Stop" button has been pressed, the MiniDisc may continue to write music data for a few seconds from its memory buffers. During this time, it may display a message ("Data Save", on at least some models) and the case will not open. After the audio data is written out, the final step is to write the TOC track denoting the start and endpoints of the recorded data. Sony notes in the manual that one should not interrupt the power or expose the unit to undue physical shock during this period

read more in http://en.wikipediawiki/MiniDisc

MINIDISC SYSTEM


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. That’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.