MiniDisc
The Mini Disc ( MD) is a system developed by the company Sony magneto- optical storage medium for digital recording and playback of music and language.
The MD was presented in May 1991, the sale of appropriate playback and recording devices began in November 1992 with the Sony MZ -1. The MiniDisc was the successor to the compact cassette positioned (CC ), but should actually the DAT cassette replace in the private sector after their success had failed in this segment. Due to the simple handling when cutting and recovering the MiniDisc also spread in the radio and recording studio. Data drives based on the MiniDisc, and special data minidisc could hardly prevail in Europe.
The range of playback and recording devices went since the advent of the MP3 player since 2003 sharply; in Europe did not only Sony itself out MD audio recorder. In Japan, however, the MiniDisc was similarly prevalent as the CD in Germany. In July 2011, Sony agrees announced that from September of the same year due to the declining demand the production of portable MiniDisc devices will set.
- 4.1 NetMD
- 4.2 Data - MiniDisc
Construction
The mini disc consists of a plastic housing with 72 × 68 mm edge length and 5 mm in thickness, similar to a 3.5 -inch floppy disk is housed protected in which the actual disc with 64 mm (2.5 inches) in diameter. The housing has one or two recesses closed by a slide, through which the disc is accessible. The slide is open until the recording or reproducing apparatus to prevent the ingress of dust. The disc has a total thickness of 1.2 mm, which is taken for the most part from the transparent polycarbonate substrate. On the upper side of the disc is located as in a CD, the data layer is protected by a cover layer from environmental influences and mechanical damage. The data is digitally stored and read without contact from the bottom of the mini disc by an infrared laser. The distance between the data tracks is in this case, depending on the playing time of the MiniDisc, 1.5 or 1.6 microns. Both the write and the read operation is carried out with a constant peripheral velocity (CLV ) of the mini- disc of 1.2 to 1.4 m / s
Audio MiniDisc
There are recordable audio discs with 60, 74 and 80 minutes capacity, of which the former but no longer produced. The music is stored in compressed ATRAC format, so that the data of a normal music CD ( 650 to 700 MB ) to a Mini Disc ( 164-177 MB) fit.
ATRAC uses, like AAC or MP3, a psychoacoustic model in order to remove although perceptible by the human ear, but no longer processed by the brain shares the music and thus save space.
The ATRAC codec was since the introduction of MD in 1992, constantly evolving. ATRAC standard uses a data rate of 292 kbps. Subsequently then the MDLP format ( ATRAC3 ) was introduced, with the to a 80 - minute disc 160 (LP2 ) or 320 ( LP4 ) fit minutes of music. The abbreviation LP stands in this case for " Long Play ". The music with 132 (LP2 ) or 66 kbps ( LP4 ) is compressed, but what causes a clearly audible deterioration in sound quality especially in LP4 mode.
MiniDisc types
There are two types of mini- discs, which basically differ in the type of data storage:
Ready -recorded mini discs
As with the CD there are also finished in the MD recorded media ( pre-recorded mini discs, pre -mastered Mini Discs). You will look like a finished recorded CD pressed machine and have this as a textured surface with " pits " and "lands ". The read-out process is also based on such a CD, that an erasure of the infrared laser light takes place at the transition points of the pits and lands by shift by a half wavelength. Finished recorded MiniDiscs are also referred to as "High Reflective Type", the laser operates in the reading operation with a power of about 0.4 mW.
Rewritable MiniDisc
The recordable MD ( Mini Disc Recordable ) contains below the reflection layer, a magnetizable layer of a terbium - iron -cobalt alloy with a relatively low Curie temperature of about 185 ° C. This layer is exposed to a temperature above the Curie point of a magnetic field, the magnetization is maintained even after cooling. In the readout process, the laser light must be on the way to the reflection layer of the MD and back through the magnetized layer. The magneto-optical Kerr effect causes a change in the polarization of the laser light depending on the magnetization direction, which is made available a special optics with Wollaston prism for signal acquisition. Rewritable MiniDiscs are also referred to as "Low Reflective Type", the laser operates in the reading operation with a power of about 0.8 mW.
Coding, write protection
Since different optical reading process are necessary for both mini disc types, the type of MD is coded mechanically via a housing bore and is read by a switch from winamp end device.
A further bore in the housing serves as an indicator as to whether the mini disc can be described, and is also sensed by a switch. In the case of re-writable discs, they can be opened and closed by a slide and serves as a protection against accidental overwriting an existing recording in ready -recorded MDs it is always open.
Devices
For audio mini discs both stationary MiniDisc decks and portable MiniDisc Walkman are available (with or without recording function ).
The MiniDisc decks were the first audio devices have a built-in buffer ( with stationary players generally six seconds in older portable devices 10 and in today's portable devices over 200 seconds), which enabled the flawless play from vibration or shock. This buffer was necessary because this system stores in sectors that do not necessarily have to be consecutive, such as after deleting a title. The audio data at a higher speed than the actual tone reproduction is required, is read into the memory before it is read out at normal speed (depending on the data rate) for the digital - analog conversion again. When the buffer is full, driving motor and lasers can be temporarily stopped. You must return to work only when the memory is almost read. This technique enables to save energy, which increases the reproduction time in portable devices.
The buffer can also be used for recording. By a " Time Machine Recording " feature can be the starting time of recording the contents of the buffer memory vorverschieben, that is, the recording also includes the final seconds before pressing the recording button.
NetMD
Since 2001 there is the opportunity to set up mini discs directly from your PC via USB ( NetMD ). This context I have to note several limitations:
Data - MiniDisc
MDs were also used for data storage, the capacity is approximately 140 MB. This MD -Data -mentioned discs differ in the color of the case of the music -MDs. There were drives for computers, cameras with MDs as a storage medium, scanners, which store data on MD, and others. Likewise, some multitrack recording devices such as Yamaha MD4 and MD8 MD -Data used for storage.
Due to the high price of the drives, also due to the licensing behavior on the part of Sony, as well as adequate availability of other similar media ( Zip, LS120, MO, and later CD -R ), this application but could not prevail.
Recording or storage method
Recordable Mini Discs use to store the data, a magneto - optical method as in the MO disk. During the writing operation, the laser operates at the bottom of the mini disc with increased output (for example 7 mW ) to selectively heat the magnetizable layer to a temperature above its Curie point. As a guide for the laser used is a applied in the production of MiniDisc guide track ( pre-groove ). Be from the top of the mini disc by the alternating field, then a small electromagnet which rests resiliently on a recording arm for rotating the minidisc, the modulated data. After cooling, the magnetization of each field is retained and is insensitive to external magnetic fields.
Before re full or partial describing a pre-recorded MiniDisc no deletion is necessary because the affected data areas are already completely re- magnetized. The data on a MiniDisc are organized similar to a floppy disk into sectors that the assignment of the MiniDisc is stored in a table of contents (User Table of Contents, TOC ). In contrast to the audio CD on which the data is stored sequentially on a spiral track, thus, individual tracks on the MD deleted, merged, will be divided and moved. Updating the TOC happens, depending on the recording device, either directly after the recording or editing, or just prior to ejection of the mini disc from the recorder or after the next power-up. In the latter case, the current - TOC data is temporarily stored in a battery-buffered RAM of the recording device.
Through the magneto- optical method, a high safety and durability of the stored data is achieved, it will be typically 30 years of data retention and more than one million write operations specified. These figures are significantly higher than those of the rewritable CD - RW, the purely optically.
Serial Copy Management System ( SCMS )
Audio MiniDisc devices feature a copy protection mechanism, the Serial Copy Management System ( SCMS ). This method allows a unique dubbing created using digital signals data carriers ( CD, MD, DAT or DCC ). Another Copy to create a second generation copy is only possible via an analog output.
However, SCMS only affects the consumer sector. Studio equipment usually ignored SCMS restrictions. Until the introduction of new copyright laws that prohibit any form of circumvention of copy protection, also devices offered, the out -filtered the SCMS bit of the digital data stream or it to "00" put ( meaning: as often copied ), so the SCMS to get around. Due to the high penetration of personal computers with digital audio inputs and outputs SCMS is however nowadays a very ineffective copy protection.
Since mid-2005, Sony has loosened the restrictive copy protection for MD -to -MD- copies for the end user. The user can since SonicStage 3.2 determine whether the copy is set or not.
The copies of copy- protected CDs to MD is prevented corresponding data on your CD by most recent CD copy protection mechanisms by " illegal", not the CD specification in the Red Book. The Sony 's copy protection Key2Audio however, makes the SCMS advantage. It causes by a set copy bit that the original CD is already considered by the SCMS as a copy and therefore can not be digitally copied.
Pros and Cons
The advantages of MiniDisc are their robustness and immunity to dirt. ( Move tracks, delete tracks, separate tracks, merge tracks, portion-wise deletion, text editing for titles, etc. ) The easy editability directly to the recording devices allow only a few other recording media. Also to mention is also the virtually unlimited Wiederbespielbarkeit ( about 1,000,000 times), the opposite DAT quick song access and 1:1 recording capability.
Portable MiniDisc devices provide extremely long battery life ( up to 135 hours). It is also noteworthy that the ATRAC format as opposed to some other currently popular on mobile players lossy formats like AAC and MP3 without detours gapless playback controls. There are various software players can simulate this for the MP3 format only.
A disadvantage is the lossy compression of the audio data. Thus, the MiniDisc for studio purposes is less suitable. The disadvantage of lossy compression was partially eliminated with the new Hi- MD, as thus the 1:1 uncompressed recording in PCM is possible. Another drawback consists in the MD compared to the DAT standard lower sampling frequency ( 44.1 kHz, compared to 48 kHz), when recording of analog sources. The resolution of the recorded on the MD data is not set in contrast to CD, because no explicit bit depth is saved because of the structure of the ATRAC codec. Through digital recordings of sources in 20 - or 24 - bit quality (or analog recording using a 20 - or 24 - bit-compatible A / D converter ) recordings via the 16 -bit standard are possible. However, players are properly equipped for playing above this standard requires ( most decks from various manufacturers as well as portable devices from Sharp or D / A converters with this ability.)
A serious disadvantage compared with DAT is that, in most older recording devices after power failure, accidental disconnection from the network or forced mechanical to early eject the disc in portable devices before the TOC (User Table of Contents) is selected, the entire recording will be lost with newer, this information is usually kept by battery in storage until they can be written at the earliest opportunity to the disc. This problem has MiniDisc albeit together with CD, CompactFlash and hard disk recorders. Exceptions to this are some professional MiniDisc recording devices and the devices from the NetMD generation who pass the preliminary, revised "pre- TOC " in the device memory before or during recording, so that the recording is preserved in each case. The website also circulate instructions to recover lost audio data ( TOC cloning). In the German minidiscforum.de a thread offering to the user the free data recovery from recordings by TOC Cloning exist.