MiniDisc system

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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.



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.


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.


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.