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Storage medium
TDK MiniDisc and AA-battery 200703.jpg
MiniDisc and AA battery for size comparison
Type Magneto-optical storage medium
capacity 60/74/80 min (audio)
size 72 mm × 68 mm × 5 mm
use Audio, data
developer Sony
idea 1991
Launch 1992
predecessor Compact Cassette , Digital Audio Tape
successor Hi-MD from July 2004
Sony MZ-1, the first MiniDisc recorder (1992)
Detailed view of the MiniDisc recorder Sony MZ-R30 from 1996
Pioneer MEH-P5500, MiniDisc car radio

The MiniDisc ( MD ) is a magneto-optical storage medium developed by Sony for the digital recording and playback of music and speech.

The MD was presented in May 1991, and sales of the corresponding playback and recording devices began in November 1992 with the Sony MZ-1. The MiniDisc was positioned as the successor to the Compact Cassette (CC) after the DAT cassette was unsuccessful in the private sector. In 1999 some Japanese suppliers offered MiniDisc players as a hi-fi system component. Because of its ease of use when cutting and recording, the MiniDisc also spread to the radio and recording studio. Data drives based on the MiniDisc as well as special data MiniDiscs could hardly establish themselves in Europe.

The range of playback and recording devices has declined sharply since the advent of MP3 players in 2003; in Europe only Sony brought out MD audio recorders . In Japan, on the other hand, the MiniDisc was as widespread as the CD in Germany. In 2004 Sony presented the revised MiniDisc HI-MD with 1 GB storage capacity. In July 2011 Sony announced, however, that from September of the same year, due to the falling demand, the production of portable MiniDisc devices would be discontinued; by March of the same year Sony had sold 22 million devices.


The MiniDisc consists of a plastic housing with an edge length of 72 mm × 68 mm and a thickness of 5 mm, similar to that of a 3.5-inch floppy disk , in which the actual disc with a 64 mm (2.5-inch) diameter is protected. The housing has one or two recesses closed by a slide, through which the disc is accessible. The slider is only opened by the recording or playback device in order to prevent dust from entering. The disc has a total thickness of 1.2 mm, most of which is taken up by the transparent polycarbonate carrier material. The data layer is located on the upper side of the disc like a CD , which is protected from environmental influences and mechanical damage by a cover layer. The data is stored digitally and read out from the underside of the MiniDisc without contact using an infrared laser . The distance between the data tracks is 1.5 or 1.6 µm, depending on the playing time of the MiniDisc. Both the writing and the reading process take place at a constant peripheral speed ( CLV ) of the MiniDisc of 1.2 to 1.4 m / s.

Audio mini disc

A spectral analysis of the uncompressed song The Power of Thy Sword shows a full bandwidth up to about 21 kHz, whereas the lower spectra of the respective files show a much lower bandwidth, which does not say much about the deterioration in sound quality. (MiniDisc frequency spectra from analog recording)

There are recordable audio MDs with a capacity of 60, 74 and 80 minutes, but the former are no longer produced. The music is saved in the compressed ATRAC format so that the data on a normal music CD (650 to 700 MB) fit on a MiniDisc (164 to 177 MB).

ATRAC uses, similar to AAC or MP3 , a psychoacoustic model to remove the parts of the music that can be perceived by the human ear but can no longer be processed by the brain, thus saving storage space.

The ATRAC codec has been continuously developed since the introduction of the MD in 1992. Standard ATRAC uses a data rate of 292 kbps. The MDLP format (ATRAC3) was subsequently introduced, with which 160 (LP2) or 320 (LP4) minutes of music can be stored on an 80-minute disc. In this case, the abbreviation LP stands for "Longplay". The music is compressed at 132 (LP2) or 66 kbps (LP4), which, however, causes a clearly audible deterioration in sound quality, especially in LP4 mode.

In contrast to the CD, the resolution of the data recorded on the MD is not fixed because, due to the structure of the ATRAC codec, no explicit bit depth is stored. Digital recordings of sources in 20 or 24 bit quality (or analog recordings using a 20 or 24 bit A / D converter) make recordings above the 16 bit standard possible. For playback above this standard, appropriately equipped playback devices are required (however, there is unlimited compatibility with devices that only have a 16-bit converter).

It should also be emphasized that the ATRAC format, in contrast to some other lossy formats currently used on mobile playback devices such as AAC and MP3, was able to handle gapless playback without detours .

MiniDisc types

There are two types of MiniDiscs, which fundamentally differ in the type of data storage:

Completely recorded MiniDiscs

As with the CD , the MD also comes with pre-recorded media (pre-recorded MiniDiscs, pre-mastered MiniDiscs). They are machine-pressed like a pre-recorded CD and, like this one, have a structured surface with "pits" and "lands". As with a CD, the readout process is based on the fact that the infrared laser light is extinguished at the transition between pits and lands by shifting it by half a wavelength. Pre-recorded MiniDiscs are also referred to as “High Reflective Type”; the laser works with a power of around 0.4 mW during the reading process  .

Rewritable MiniDisc

The recordable MD (recordable MiniDisc) contains a magnetizable layer made of an iron-terbium-cobalt alloy with a relatively low Curie temperature of about 185 ° C below the reflective layer . If this layer is exposed to a magnetic field at a temperature above the Curie point, the magnetization is retained even after cooling. During the readout process, the laser light must pass through the magnetized layer on its way to the reflection layer of the MD and back. The magneto-optical Kerr effect causes a change in the polarization of the laser light depending on the direction of magnetization, which is made usable for signal generation via special optics with a Wollaston prism . Rewritable MiniDiscs are also known as "Low Reflective Type", the laser works with a power of around 0.8 mW during the reading process.

TDK 80-Min-MD with opened protective slide

Coding, write protection

Since different optical reading processes are required for both MiniDisc types, the MD type is mechanically coded via a housing bore and is read by the playing device using a switch.

Another hole in the housing serves as an indicator as to whether the MiniDisc can be written on and is also scanned by a switch. In the case of rewritable MDs, it can be opened and closed with a slide and thus serves as protection against inadvertent overwriting of an existing recording, with finished MDs it is always open.


Sharp MD-MT18 MiniDisc Recorder
MiniDisc deck Sony MDS-JE780 (2002-2005)

Both stationary MiniDisc decks and portable MiniDisc Walkman (with or without a recording function) were available for audio MiniDiscs . There were also many other types of devices with built-in minidisc drives, for example car radios , radio recorders or compact systems .

The MiniDisc devices were the first audio devices to have a built-in buffer (usually six seconds on stationary playback devices, around 10 seconds on older portable devices and over 200 seconds on today's portable devices), which enabled error-free playback in the event of vibrations or bumps. This buffer was necessary because this system stores in sectors that do not necessarily have to follow one another, for example after a title has been deleted. The audio data are read into the memory at a higher speed than required for the actual sound reproduction before they are read out again at normal speed (depending on the data rate ) for the digital-to-analog conversion . When the buffer memory is full, the drive motor and laser can be stopped temporarily. You don't have to go back to work until the memory is almost full. This technology enables energy savings, which extends the playback time of portable devices.

The buffer memory can also be used for recording. The function known as “Time Machine Recording” allows the start time of the recording to be advanced by the contents of the buffer memory, which means that the recording also includes the last few seconds before the record button was pressed.


Sony MZ-RH1, the last (Hi) MD Walkman built by Sony

Since 2001 it has been possible to record onto MiniDiscs directly from the PC via USB (NetMD). However, several restrictions had to be observed:

  1. Audio data transferred to an MD cannot be transferred to another PC.
  2. Recordings made via the microphone input cannot be transferred to the computer via USB. The product description, as well as the manual for the NetMD models, did not clearly point to this fact, which resulted in massive complaints. Sony responded by providing a file conversion tool for the successor models with the designation Hi-MD , with which it is possible, under the conditions set by Sony, to record analogue recordings of Hi-MD (but not of conventional MDs) to be copied to the computer via a USB cable and converted into WAV files there. The program does not work with the NetMD models.
  3. The transmission quality is limited to a maximum of 132  kbps , i.e. corresponds to LP2. You can also transfer music in SP mode to maintain compatibility with older MD devices. However, the quality remains at the level of 132 kbps.
  4. Only MP3, WMA and WAV files can be transferred to MD, and only within specified bit rates and frequencies. It is also possible to transfer audio CDs.
  5. The original files are not transferred, but instead a lossy conversion into the ATRAC3 format takes place.
  6. Transfer software is required which converts the audio files to ATRAC and transfers the data to the MD. The user can choose between different programs. The most common are OpenMG Jukebox, SonicStage, and NetMD Simple Burner. There is also a plug-in for RealPlayer .
  7. An MD that was recorded via NetMD can no longer be edited or deleted on non-NetMD capable devices. The reason is that otherwise the transfer rights also stored on this MD, which are transferred back when the MD is deleted on the PC, would be lost and you could unintentionally lose the NetMD transfer rights step by step. This lock was still useful when a maximum of three transfers per piece of music were allowed by the Sony software. This restriction has now been removed. However, there is also the option of buying music online from Sony's own “Music Store”. Files downloaded there are usually restricted in their transfer rights again.

In 2006, Sony launched the MZ-RH1, the last portable MD device on the market. With this model it finally became possible to copy conventional MDs to the PC via USB with practically no restrictions (the only exception: titles transferred via NetMD). The transfer of pre-recorded MDs as well as recordings via the digital input - regardless of any SCMS copy protection (see below) - was not restricted in any way with this model. The use of an MZ-RH1 is still the only way to copy MDs to another data carrier faster than in real time without loss.

Data MiniDisc

MDs have also been used for data storage, with a capacity of around 140MB. These discs, called MD data, differ in the color of the casing from the music MDs. There were drives for computers, cameras with MDs as storage media, scanners that save data on MDs, and more. Also, some multi-track recording devices such as the Yamaha MD4, MD8 and Tascam Portastudio 564 used MD data for storage.

Due to the high price of the drives, also due to the licensing behavior on the part of Sony, as well as sufficient availability of other similar data carriers ( Zip , LS120 , MO , later also CD-R ), this application was not able to establish itself.

Recording or storage method

Writable MiniDiscs use a magneto-optical process to store the data, like the MO disk . During the writing process, the laser on the underside of the MiniDisc works with increased power (approx. 7 mW) in order to selectively heat its magnetizable layer to a temperature above its Curie point . A guide track ( pregroove ) applied during the manufacture of the MiniDisc serves as a guide for the laser . The data is then modulated from the top of the MiniDisc by the changing field of a small electromagnet that rests resiliently on a writing arm on the rotating MiniDisc. After cooling, the magnetization of the individual fields is retained and is insensitive to external magnetic fields.

No erasing process is necessary before completely or partially rewriting an already recorded MiniDisc, as the data areas concerned are completely re-magnetized anyway. The data on a MiniDisc is organized into sectors in a similar way to a floppy disk , the assignment of the MiniDisc is stored in a table of contents (User Table of Contents, UTOC). In contrast to the audio CD, on which the data is stored sequentially on a spiral track, individual tracks on the MD can be deleted, combined, divided and moved. The UTOC is updated - depending on the recording device - either directly after the recording or editing process or before the MiniDisc is ejected from the recording device or after it is next switched on. In the latter case, the current UTOC data is temporarily stored in a battery-backed RAM of the recording device .

The magneto-optical process achieves a high level of security and longevity of the stored data, typically 30 years of data retention and more than a million write operations are specified. These numbers are significantly higher than those of the rewritable CD-RW , which works purely optically.

Serial Copy Management System (SCMS)

Audio MiniDisc devices have a copy protection mechanism , the Serial Copy Management System (SCMS). This process allows a one-time transfer of data carriers (CD, MD, DCC or DAT ) created using digital signals . Another copying to create a second generation of copies is only possible via an analog output.

However, SCMS only affects the consumer area. Studio equipment usually ignores SCMS restrictions. Until the introduction of the new copyright laws , which forbade any kind of circumvention of copy protection, devices were also offered that filtered the SCMS bit out of the digital data stream or set it to "00" (meaning: can be copied as often as required), so that Bypass SCMS. Due to the widespread use of PCs with digital audio inputs and outputs, however, SCMS is nowadays a very ineffective copy protection.

Since mid-2005, Sony has relaxed the restrictive copy protection for MD-to-MD copies for end users as well. Since SonicStage 3.2, the user can determine whether or not copy protection is set.

The copying of copy-protected CDs to MD is prevented by most current CD copy protection mechanisms through "illegal" data on the respective CD that does not comply with the CD specification in the Red Book . Sony's own copy protection Key2Audio, however, makes use of the SCMS. With a set copy bit, it ensures that the SCMS already regards the original CD as a copy and therefore cannot be digitally copied.

Advantages and disadvantages

The minidisc spread on the market at a time when the CD in the form of prerecorded sound carriers had already found its way into most households, but private sound recordings were still primarily made on analog compact cassettes . At that time it represented a comparatively inexpensive and user-friendly way of making low-loss digital sound recordings. This is particularly true of the portable MD recorders, which up until the 2000s were the only ones and, above all, the smallest , alongside DAT recorders , which were mainly used in the professional sector, and the DCC recorders that were only produced for a few years portable digital audio recorder. The advantages of the MiniDisc compared to magnetic tape-based formats were the quick and convenient access to individual titles, the robustness and insensitivity to dirt as well as the ease of editing (moving, deleting, separating, merging, section-by-section deletion, text editing for titles, etc.) directly on the recording devices . Also to be mentioned is the practically unlimited replayability (according to the manufacturer about 1,000,000 times) and the high long-term durability due to the magneto-optical functional principle.

One disadvantage is the lossy compression of the audio data. This makes the MiniDisc less suitable for studio use. In the first ATRAC version, the loss of quality due to compression was still clearly audible, but the codec has been continuously improved and has been acoustically transparent since version 3.5 (released in 1996) at the latest . The disadvantage of lossy compression was partially eliminated with the new Hi-MD , as it also made uncompressed 1: 1 recording in PCM possible.

A serious disadvantage compared to DAT was that with most older recording devices after a power failure, accidental disconnection from the mains or forced mechanical ejection of the disc too early on portable devices before the UTOC (User Table of Contents) was saved, the entire recording was lost. in newer devices this information was usually stored in the memory by battery until it could be written to the disc at the next opportunity. MiniDisc has this problem in common with CD, CompactFlash and hard disk recorders. Exceptions to this are some professional MiniDisc recording devices and devices from the NetMD generation , which store the temporary, changed “Pre-UTOC” in the device memory before or during the recording, so that the recording is retained in any case. Instructions are also circulating on the Internet to restore lost audio data (TOC cloning). In the German there is a thread in which users offer free data recovery from recordings through TOC cloning.

See also

Web links

Commons : MiniDisc  - collection of pictures, videos and audio files

Individual evidence

  1. test, Stiftung Warentest 11/1999, seven minidisc recorders for 500 to 800 marks as well as a noble CD recorder ... in the test , accessed on May 29, 2020.
  2. Sony MZ-1
  3. ^ The Sony MiniDisc. Retrieved July 30, 2010 .
  4. ↑ In the meantime: Sony launched the last MiniDisc player (February 2, 2013) , accessed on May 29, 2020.
  5. "Sony To Wind Up MiniDisc Walkman Shipments", July 7, 2011 ( Memento of July 11, 2011 in the Internet Archive )
  6. a b FAQ - Basic knowledge about the MD (accessed on July 30, 2010) ( Memento from March 26, 2010 in the Internet Archive )
  7. FAQ - What is ATRAC / The development of ATRAC (accessed on July 30, 2010) ( Memento from March 25, 2010 in the Internet Archive )
  8. [1] FAQ: MDLP ("Long-Play") mode (accessed on July 30, 2010)
  9. [2] FAQ: Disc topics (accessed on July 30, 2010)
  10. [3] MiniDisc Technology (accessed July 30, 2010)
  11. 2020, Sony MDS-JE780 , accessed May 29, 2020.
  12. [4] FAQ: Minidisc Specific Topics (accessed on July 30, 2010)
  13. [5] FAQ: NetMD Topics (accessed July 30, 2010)
  14. [6] FAQ: Disc topics (accessed on July 30, 2010)
  15. Jerry D. Gibson, Toby Berger, Tom Lookabaugh, David Lindbergh: Digital Compression for Multimedia: Principles and Standards , 1998, p. 287
  16. [7] - Description of saving MD recordings (TOC cloning) (accessed on July 30, 2010)