MiniDisc: A Technical White Paper

A Digital Audio Storage Medium for Personal Multitrack Recording

July 12, 1996 -- Not only has digital audio changed the techniques by which music and sound are being recorded, but it has changed the media formats upon which it is being stored. DAT became the first digital audio storage medium that was originally launched as a consumer format and became a standard for digital audio and data storage. More recently, new digital multitrack audio recording systems utilize audio-specific media formats as well as a media that was originally developed for video and data recording. The widespread use of S-VHS and 8mm video tapes for ADAT and DTRS recording, and the use of Exabyte tapes and CD-R discs for mastering, are examples of this trend. The recent introduction of MiniDisc for digital multitrack audio recording is yet another.

MiniDisc is an audio storage medium which was introduced for consumer use and for professional stereo recording and playback. It is also used as a portable, high-capacity, digital re-recordable storage medium for personal computers. The media provides data storage of up to 140 megabytes on a single 2.5-inch magneto-optical disc and is rewritable up to 1 million times. The disc is not exposed to the environment; it is encased in a plastic cartridge similar to a 3.5-inch floppy disc. It is extremely resistant to scratches and dust, as well as relatively invulnerable to stray magnetic fields. The format conforms to Rainbow Book Part II standards.

This innovation has also made possible a new generation of personal audio production four-track recorders, which offer the same inexpensive, portable characteristics necessary for personal multitrack production, with the added features of random access, digital sound quality and rewrite durability. The use of MD for multitrack recording is supported by Sony, Yamaha and Tascam.

Media Characteristics

The MD format offers the latest advances in media technology, including small size (2.5 inch), magneto-optical storage, portability and durability, making it an ideal recording medium. It has been optimized for data and digital multitrack recording applications, offering a highly reliable recording layer with extremely low error rates and excellent long-term performance.

MiniDisc's unique Magnetic-Field Modulation Direct Overwrite Process makes it a highly efficient storage medium for multitrack recording. An MD drive alternates magnetic fields when writing data to the disc. The beam of a small semiconductor laser operates at constant intensity, heating a small spot on the recording medium above the Curie point (about 180 degrees C), and writes data as a binary code ("1" or "0"), depending on the polarity of the magnetic field applied by the overwrite head on the opposite side of the disc. The overwrite head is modulated by the input signal. This technique, combined with a highly durable recording layer, results in the medium's ability to store high-density data and can be re-recorded frequently. Both of these attributes are necessary in the music production environment.

A new tightly sealed cartridge shell has been designed with a long shutter mechanism to protect the disc from dust, dirt and other contaminants. What's more, the multitrack drives have been designed to read a media ID prewritten in the Table of Contents (TOC) of each disc in order to determine whether the disc has been inserted.

As an alternative to the analog audio cassette, the MD format offers significant sound quality improvements. The first generation of MiniDisc personal multitrack recorders delivers a sampling rate of 44.1kHz and a maximum recording time of 37 minutes for four tracks (or either 74 minutes of stereo or 148 minutes of mono). The media is interchangeable and compatible between the various manufacturer hardware products

The most significant development has been a radical improvement in sound quality for the MD format since its introduction by Sony as a consumer-only format in 1992. Sony's MD recording system is now being acclaimed by recording engineers and musicians alike as a leading solution for music production.

Applications

MD overcomes the limitations of the analog audio cassette for low-cost personal multitrack recording. Typically used for song-writing, pre-production or demo work, personal multitracks require a storage medium that is inexpensive, portable and robust enough to handle extensive rerecording. The MD format offers all these features plus sound quality that approaches Compact Disc. As a magneto-optical disc, the MD format is significantly more durable. And as a random access medium, MD provides increased track access capabilities over tape-based media.

For more information, visit their web site at www.sony.com.