MiniDisc

This article is about the Sony storage format. For the Gescom album, see Minidisc (album). For the IBM minidisk, see VM (operating system).

MiniDisc

The Sony MZ1 MiniDisc player, the first to hit the market in 1992.
Media type	Magneto-optical disc
Encoding	ATRAC, linear PCM (with Hi-MD)
Capacity	80 min (standard MiniDisc), up to 45 hours of audio (1 GB capacity) (with Hi-MD)
Read mechanism	780 nm laser
Write mechanism	Magnetic field modulation
Developed by	Sony
Usage	Audio storage, Data storage (with Hi-MD)

Optical discs

Optical disc Optical disc drive Optical disc authoring Authoring software Recording technologies Recording modes Packet writing
Optical media types
Blu-ray Disc (BD): BD-R, BD-RE DVD: DVD-R, DVD+R, DVD-R DL, DVD+R DL, DVD-R DS, DVD+R DS, DVD-RW, DVD+RW, DVD-RAM, DVD-D, DVD-A, HVD, EcoDisc Compact Disc (CD): Red Book, CD-ROM, CD-R, CD-RW, 5.1 Music Disc, SACD, Photo CD, CD Video (CDV), Video CD (VCD), SVCD, CD+G, CD-Text, CD-ROM XA, CD-i Universal Media Disc (UMD) Enhanced Versatile Disc (EVD) Forward Versatile Disc (FVD) Holographic Versatile Disc (HVD) China Blue High-definition Disc (CBHD) HD DVD: HD DVD-R, HD DVD-RW, HD DVD-RAM High definition Versatile Multilayer Disc (HD VMD) VCDHD GD-ROM MiniDisc (MD) (Hi-MD) Laserdisc (LD) (LD-ROM) Video Single Disc (VSD) Ultra Density Optical (UDO) Stacked Volumetric Optical Disk (SVOD) Five dimensional disc (5D DVD) Nintendo optical disc (NOD)
Standards
SFF ATAPI/MMC Mount Rainier (packet writing) Mount Fuji (layer jump recording) Rainbow Books File systems ISO 9660 Joliet Rock Ridge / SUSP El Torito Apple ISO 9660 Extensions Universal Disk Format (UDF) ISO 13490
See also
History of optical storage media High definition optical disc format war
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A MiniDisc (MD) is a magneto-optical disc-based data storage device initially intended for storage of up to 74 minutes and, later, 80 minutes, of digitized audio. In the form of Hi-MD, it has also developed into a general-purpose storage medium.

MiniDisc was announced by Sony in September 1992 and released that November for sale in Japan and in December for the USA and Europe.^[1] The music format was originally based exclusively on ATRAC audio data compression, but the option of linear PCM digital recording was later introduced to attain audio quality comparable to that of a compact disc. MiniDiscs were very popular in Japan but made a limited impact elsewhere.^[2]

Market history

Sony's MiniDisc was one of two rival digital systems introduced in 1992, that were both targeted as a replacement for the Philips analog cassette audio tape system: the other was Digital Compact Cassette (DCC), created by Philips and Matsushita. Sony had originally intended for Digital Audio Tape (DAT) to be the dominant home digital audio recording format, replacing the analog cassette. Unfortunately, due to technical delays, DAT was not launched until 1989, and by then, the U.S. dollar had fallen so far in relation to the yen, the introductory DAT machine Sony had intended to market for about $400 in the late 1980s now had to retail for $800 or even $1000 to break even, putting it out of reach for most users.

Relegating DAT for pro use, Sony immediately set to work to come up with a simpler, more economical digital home format. By the time Sony came up with MiniDisc in late 1992, rival Philips introduced a competing system, DCC (the digital compact cassette). This created marketing confusion very similar to the Beta vs. VHS battle of the late 1970s and early 1980s. Sony attempted to license MD technology to other manufacturers, with JVC, Sharp, Pioneer, Panasonic and others all producing their own MD systems. However, non-Sony machines were not widely available in North America, and companies like Technics and Radio Shack tended to promote DCC instead.

Despite having a loyal customer base (primarily musicians and audio enthusiasts), MiniDisc met with only limited success. It was relatively popular in Japan during the 1990s but did not enjoy comparable sales in other world markets. Since then, Recordable CDs, flash memory and HDD-based digital audio players introduced in 1998 have become increasingly popular as playback devices.

The initial low uptake of MiniDisc was attributed to the small number of pre-recorded albums available on MD as a relatively small number of record labels embraced the format. The initial high cost of equipment and blank media was also a factor. Stationary MiniDisc-player/recorders never got into the lower price ranges, and most consumers had to hook the portable player to the hi-fi in order to record. This inconvenience contrasted the earlier common use of cassette player/recorders as a more or less standard part of an ordinary hi-fi set-up, even before the break-through of portable cassette tape players. Pre-recorded MDs disappeared from the market rather suddenly in the late 1990s.

MiniDisc technology was faced with new competition from the recordable compact disc (CD-R) when it became more affordable to consumers in 1995. Initially, Sony believed that it would take a decade for CD-R prices to become affordable (starting at about $12 per blank CD-R disk in 1994). But the prices fell very quickly, to the point where CD-R blanks sank below $1.00 by the end of the 1990s, compared to more than $2.00 for similar 80-minute MiniDisc blanks.

The biggest competition for MiniDisc came from the emergence of MP3 players. With the Diamond Rio player in 1998 (eclipsed by the iPod in 2001), the mass market began to eschew physical media in favor of file-based systems, rendering cassette- and disc-based formats obsolete by the end of the 2000s.^{[citation needed]}

By 2007, because of the waning popularity of the format and the increasing popularity of solid-state MP3 players, Sony was producing only one model, the Hi-MD MZ-RH1 (also available as the MZ-M200 in North America packaged with a Sony microphone and limited Macintosh software support).^[3]

The introduction of the MZ-RH1 allowed users to freely move uncompressed digital recordings back and forth from the MiniDisc to a computer without the copyright protection limitations previously imposed upon the NetMD series. This allowed the MiniDisc to better compete with HD recorders and MP3 players. However, even pro users like broadcasters and news reporters had already abandoned MiniDisc in favor of solid-state recorders, due to their long recording times, open digital content sharing, high-quality digital recording capabilities and reliable, lightweight design.

On July 7, 2011, Sony announced that it would no longer ship MiniDisc Walkman products as of September 2011.^[4]

MD Data

MD Data, a version for storing computer data, was announced by Sony in 1993 but never gained significant ground. Its media were incompatible with standard audio MiniDiscs, which has been cited as one of the main reasons behind the format's failure.^{[citation needed]}

MD Data could not write to audio-MDs, only the considerably more expensive data blanks. In 1997, MD-Data2 blanks were introduced, which held 650 MB of data. They were only implemented in Sony's short-lived MD-based camcorder as well as a small number of MultiTrack Recorders; Sony's MDM-X4, Tascam's 564 (which could also record using standard MD-Audio discs, albeit only 2 tracks), and Yamaha's MD-8, MD-4, & MD4S.

The Hi-MD format, introduced in 2004, marked a return to the data storage arena with its 1 GB discs and ability to act as a USB drive. Hi-MD units allow the recording and playback of audio and data on the same disc, and are compatible (both audio and data) with standard MiniDisc media. (An 80 minute Minidisc blank can be formatted to store 305MB of data)

Design

Physical characteristics

Memorex Mini-Disc Minidisc in cartridge (left), exposed minidisc (right) and protective cartridge holder (rear) Sony MiniDisc Recorder

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 premastered. 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 polarisation 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 were 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.

MiniDiscs use a mastering process and optical playback system that is very similar to CDs. The recorded signal of the premastered pits and of the recordable MD are also very similar. 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

Comparison of several forms of disk storage showing tracks (not-to-scale); green denotes start and red denotes end.
* Some CD-R(W) and DVD-R(W)/DVD+R(W) recorders operate in ZCLV, CAA or CAV modes.

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 SonicStage 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 defragmenting 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

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 is 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 bitrates; 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 lossy 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

MiniDisc Recorder MDS-81, normally used in recording or broadcast radio studios.

Detail view of the MZ-R30 MiniDisc recorder of Sony (1996)

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.

Format extensions

MDLP

In 2000, Sony announced MDLP (MiniDisc Long Play), which added new recording modes based on a new codec called ATRAC3. In addition to the standard, high-quality mode, now called SP, MDLP adds LP2 mode, which allows twice as much recording time (160 minutes on an 80 minute disc) of good-quality stereo sound, and LP4, which allows four times more recording time (320 minutes on an 80 minute disc) of medium-quality stereo sound.

The bitrate of the standard SP mode is 292 kbit/s, and it uses separate stereo coding with discrete left and right channels. LP2 mode uses a bitrate of 132 kbit/s and also uses separate stereo coding. The last mode, LP4 has a bitrate of 66 kbit/s and uses joint stereo coding. The sound quality is noticeably poorer than the first two modes, but is sufficient for many users.

Tracks recorded in LP2 or LP4 mode play back as silence on non-MDLP players.

NetMD

NetMD recorders allow music files to be transferred from a computer to a recorder (but not in the other direction) over a USB connection. In LP4 mode, speeds of up to 32× real-time are possible and three Sony NetMD recorders (MZ-N10, MZ-N910, and MZ-N920) are capable of speeds up to 64× real-time. NetMD recorders all support MDLP.

NetMD is a proprietary protocol, and it is currently impossible to use it without proprietary software, such as SonicStage. Thus, it cannot be used under non-Windows machines. A free *nix based implementation, libnetmd, is being developed, but it cannot be used to upload music (as of December 2005^[update]).

Hi-MD

Main article: Hi-MD

Hi-MD is the further development of the MiniDisc-format. It was introduced in 2004. Hi-MD media will not play on non Hi-MD equipment, including NetMD players.

Recording modes

Modes marked in green are available for recordings made on the player, while those marked in red are only available for music downloaded from a PC. Capacities are official Sony figures; real world figures are usually slightly higher. Second generation Hi-MD players also support MP3 compression natively, in a multitude of bitrates. Recently, 352 kbit/s and 192 kbit/s ATRAC3plus have also been made available for 1st and 2nd generation Hi-MDs.

Name	Bitrate (kbit/s)	Codec	Availability and capacity (min)
			Standard player	MDLP player	Hi-MD player
			80 minute disc			80 minute disc (HiMD formatted)	1 GB Hi-MD disc
Stereo SP	292	ATRAC	80	80	80	n/a	n/a
Mono SP	146	ATRAC	160	160	160	n/a	n/a
LP2	132	ATRAC3	n/a	160	160	290	990
-	105	ATRAC3	n/a	127	127	370	1250
LP4	66	ATRAC3	n/a	320	320	590	1970
-	48	ATRAC3plus	n/a	n/a	n/a	810	2700
Hi-LP	64	ATRAC3plus	n/a	n/a	n/a	610	2040
Hi-SP	256	ATRAC3plus	n/a	n/a	n/a	140	475
PCM	1411.2	Linear PCM	n/a	n/a	n/a	28	94

See also

• Digital Audio Tape (DAT)
• Fidelipac
• Universal Media Disc (UMD)

References

1. ^ Sony history Retrieved 19 September 2009
2. ^ Music On The Move: MiniDisc
3. ^ Sony MZ-RH1 User Manual
4. ^ Sony To Wind Up MiniDisc Walkman Shipments

External links

• MiniDisc Community Portal
• MiniDisc.org FAQ
• MiniDisc Forum by Sony Insider
• Audio T-Board
• Linux and Sony MiniDisc players
• The Difference between Type-R and Type-S