[I]In 1992 the MiniDisc system was introduced in the consumer audio market as a new digital audio playback and recording system (Fig. 1). 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. In addition, the size of the 12-cm disc was easy to handle compared to that of the LP. The longer lifetime for both the media and the player strongly supported the acceptance of the CD format. The next target of development was obviously to be the rewritable CD. SONY and Philips jointly developed this system and made it a technical reality in 1989. 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, and Sony felt that the compact cassette system was approaching the end of its format life. 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).
Magneto-optical disc recording technology has been used for computer data storage system for several years. Based on this technology, we had developed direct overwriting technology with a similar recording density as Compact Disc. Additionally, we employed a shock-resistant memory control for portable use and applied a digital audio compression system called ATRAC (Adaptive TRansform Acoustic Coding) that enabled us to use a 64-mm disc size. Recent technological improvement of semiconductors helped to realize this technology. [/I]