(Original German Page)


Characteristics of the MiniDisc in the overview
System data of the MiniDisc
The disks
The technique
Buffer for branch bypass
Optional accesses
Signal format
MD scanner
ATRAC Datenkompression
Magnetooptic recording
Magnetic field modulation

Since 1970 Sony develops technologies for optical disk memories with the target, preference/advantage of the mode of operation without mechanical contact between carriers and recording read head with high memory density, long life span, to begin optional rapid access and low memory costs for recording and playback. The application steps were video disk, CD and CD ROM. 1988 the series by repeats recordable magnetooptic disk for the data storage completed, the MiniDisc (MD). The possibilities, which the MiniDisc within the area of the audiovisual media in the future opens, are hardly to be over-looked today.

Base of the digital storage medium is a disk-shaped carrier with substantially smaller dimensions than the CD, however with the same advantage of the rapid, optional access to any place of the recording, like that as it the users today from that CD is used. During playback and recording the utilization of the modern mechano optical or the magnetooptic technique and the effective audio data reduction leads too uerst compact dimensions of disk and device. The contactless, wear-free mode of operation ensures a high in connection with the digital audio technique, of the number of the playing or recordings independent..tone quality. During playback the effects of Sten or vibrations on the device electronically balanced and so the high quality of the digital technique with easier, comfortable and unproblematic handling achieved, like that as it for a trend-setting, portable system is indispensable.

Characteristics of the MiniDisc in the overview

System data of the MiniDisc

Spieldauer in min max. 74
Cartridge dimensions in mm 72 x 68 x 5
Disk data  
Diameter in mm 64
Thickness in mm 1,2
Diameter centering borehole in mm 11
Diameter intake area in mm 29
Diameter beginning of modulation in mm 32
Track upward gradient in m 1,6
Recording or scanning speed in m/s 1.2... 1,4
Audio data  
Channels 2 (monomono/mono)
Frequency range in cycles per second 5...,20,000
Dynamics in dB 105
Flutters not measurably
Signal format  
Sampling rate in kHz 44,1
Source quantization in bits 16
Compression system ATRAC
Modulation system EFM
Error correction system CIRC
Optical parameters  
Wavelength of the laser light in Nm 780
Diameter of the laser mark in m 0,9
Laser performance during recording in mW 5 (max.)
Recording system magnetic field modulation

The disks

The two remarks differ in special functional details. The dimensions are identical, s. fig. 3. The disk is centered like the CD in the central hole. An additionally brought in disk from magnetic material supports the mounting plate and stabilization of the disk in the Gert. Thus can be omitted pressure temples of " above ", how with D-SWITCHES far spreads, not least also due to ' the small diameter and the smaller mass to MD in the comparison to CD.
The execution designated for the selling to recorded music by disk manufacturers corresponds in structure and production technology that CD. A deletion or berschreiben this recording is impossible. The signals are mechanically casted in a pit structure in the surface of the disk exactly the same as with that CD during the production process and reflected for the optical selection. Thus the low-priced production is possible in large quantities in spraying technology for f 11. The allocation of the disk surface is illustrated in the fig. 4. The table of contents TOC is brought in with the production in the intake area. Track arrangement, pit, slab thickness and material correspond to that CD, s. fig. 5. The disk is constantly in a cartridge accommodated and so protected from damage. For the scanning the receipt is necessary only from a page. For it before seen slot is locked outside of the device.
The tapable MiniDisc operates in the magnetooptic procedure and makes from the magnetic field modulation use. The disks can practically arbitrarily often berschrieben to become.
This technology presented by Sony 1989 operate for the first time with a focused laser beam and a closely limited magnetic field, which affect the recording place of the rear side of the disk. Only this special arrangement is able to make a new recording. That protects the durability of a recording. The Grundkper of the disk squirted from polycarbonate trgt the groove structure with the time code (s. of optional ones access). Fr magneto the optical function ensures the layer structure shown in the fig. 6. The magnetically effective layer from rare demetallen (terbium of ferrites cobalt) is embedded in auxiliary layers, which protect a high Leistungsfhigkeit with small power demand and which ensure reflection of the laser light. This structure works satisfactorily for some years with MO memory in the computer engineering. The effective layer permitted on the one hand that describe (with a new on drawing nung) from more ber one million cycles without Oualitaetsminderung and protect on the other hand a good long-term stability. The MO recording requires the receipt to both pages of the disk, therefore verft this cartridge more ber reciprocal openings, which are locked by slidegate valves outside of the device again. The inscription surface precipitates thereby quite small.Bild 6

Bild 3: Abmessungen der MD
Bild 4
Bild 5

The technique

The circuit diagram of a MiniDisc of recorder (fig. 7) shows a large bereinstimmung with the structure of a D-PLAYERS. The adjustment of the data to the optical channel, which can be stored, ernimmt the modulation system EFM (Eight to of Fourteen modulation). It tunes CD just like the error correction system CIRC (CROSS Interleave Reed Solomon code) with that erein. Additional modules are brckungsschalturig the data compression, the Sprungber and the magnetic recording heading. Digital ones and outputs operate like lich with 16 bits at 44.1 kHz sampling rate. The system data are to be inferred from the board.

Bild 7: Blockschaltbild

Buffer to the Sprungberbrkung

With the practical An.wendung of trans portable optical memory has itself branching the scanner than sequence of Erschtterungen or Sten, which affect from auen the playing Gert, when much strend herausge places. By Einfgen of a semiconductor memory into the signal path it succeeded to reduce the effects of such Strun towards crucial (Shock Resistant MEMORY /. Fr the function of this buffer is helpful the Datenkom pression on approximately 1/5 the origin data, available in the system, by the ATRAC module. The selection of the information - each sector trgt its own address -, cherten on the disk in sectors gebndelt gespei, takes place with a Signalflu from 1,4 Mbit/s. Due to the data reduction however only a continuous Signalflu of approximately 0.3 Mbit/s is necessary. This means, since the selection points more normally effected in Schben. These data flieen into a buffer, fig. 8. A semiconductor buffer with a Speicherkapazitt of 1 Mbit knows the signals f about 3 s spei chern, with 4 Mbit is 10 s berbrck bar. Fig. 9 clarifies in another representation and gives a comparison to CD, with which that betrgt signal flu constantly 1.4 Mbit/s. Lt the optical scanner as consequence of one of auen pltzlichen Erschtterung its correct position kenden on the Gert einwir, then remains without Einflu on the signal more cher given from the Spei, however the memory empties thereby. After Abklin towards the Strung looks up the scanner the last correct position well-known with the help of the address and fllt the memory with the max. signal flow of 1,4 Mbit/s without Unterbre chung, in most Fllen after 1 s of the buffers is again so there gefllt already and reading in in intervals is again taken up (fig. 10).

Bild 8

Bild 9

Bild 10

Optional accesses

F the system MiniDisc is the optional access of special importance, because he help not only to a high convenient operation, but is functionally necessary also in connection with the beforehand described Sprungberbrkung. Only playback MDs of industrieller production carry a passing through time code and a table of contents (TOC, Table OF Con tent) like the CD. That protects the rapid and direct access. The f the recording " Leer" Discs intended (Recordable MiniDisc) contain injected grooves f the Frung of the recording playback laser (Pre Groove) with the production of the carrier. The spiral formed by the groove are erlagert additional deflections (some tenth micrometers) in seitenschrift, fig. 11. They form a time code with a Auflung of 13,3 ms in coded form. Thus is the optional access independently of the actual recording secured. The special system is called ADIP (ADDRESS in Pre Groove). For comfortable handling area of the track a field f contents a directory UTOC (user Table OF CONTENTS), which can be arranged from the user, is contained of the recorded disk in the initially, which structures on the time code. As is shown in the fig. 12, modifications in the table of contents are parallel realizable to modifications of the stored information in a simple manner by editing.
The even Bedienungsmlichkeiten, which offers the optional access with short access times, is mlich only with a berrungslos scanned scheibenfmigen carrier.

Bild 11
Bild 12

Signal format

A modern and flexible signal format, which is very similar to the standard CD ROM, mode 2, uses the MD. The data won with the help of the data compression system ATRAC are geschtt with the help of the data security system CfRC before errors and adapted with the modulation system EFM to the special conditions of the optical channel. Both indexing steps worked satisfactorily with that CD.
In the format CD ROM, mode 2, from 98 following each other D-FRAMEWORKS (Frames) sectors are formed, for s. fig. 13. Each sector verft it sync signals in the heading (header) and a complete address. The equivalent play time amounts to 13.3 ms, with altogether 2352 byte contents is to 2332 byte f data to the Verfung. Spreading (Interleaving) in the IRC CODER that CD amounts to 14.5 ms (according to 108 frameworks) and is thus longer than a D-SECTOR f1 ]. With the education of the Bdel (cluster) the MD for the adjustment of the length additionally to the 32 data sectors four further sectors are eingeft. A sector f Subcodedaten (2332 byte) and the three further, than links (link second gate) defined, begun with the tapable MD f data security CIRC. In the interest of sufficient spreading a parity block is recorded forwards and a further after the actual data. F this nesting is used during the recording the RAM, which serves f the Sprungunterdrkung during playback as buffer. The recording of a only playback MD takes place with a continuous signal flow, which already contains the IRC DATA, and which are to four additional sectors f Subcodedaten to the Verfung.
The ATRAC Coder compresses the audio data on 1/5 of their ursprunglichen volume. It supplies the subsequent treatment to f with sucked. Groups of sounds with 424 byte, ever 212 of the left and of the right channel. Altogether eleven of such groups of sounds are drawn in two following each other sectors on. s. Fig. 14. Each sector covers thereby 5 x 424 + 1 x 212 = 2332 data bytes. 32 sectors data and 4 addition sectors form a Bdel. Such Bdel forms the smallest recording unit of the tapable MiniDisc.

Bild 13
Bild 14

MD scanner

The different type of the signal storage of both disk types of the MD requires a special, on the different request at fit optical scanner. A normal optical scanner f CD fails to a MO recording with the scanning. With the help of a polarizing beam splitter detecting the different polarization directions succeeds to a MO recording with the scanning. According to fig. 15 reflects on the surface (country) a CD focused laser beam (about 0.5 mW) with nonexistence of a pit such as light, while in the pit the quantity of light is clearly reduced (for instance on 25 %). this difference f the signal production used, whereby the actual information in the ergaengen between country and pit is stored (EFM modulation, transition = 1; no transition = 0 [ 1)1). The signals, which supply the two optical recipients with the scanning of a recording, are added, s. fig. 16. During the scanning of a magnetooptic disk, recordingable MD, is thus used appearance the called Kerr effect out, with which a polarized light beam under the influence of different directions of magnetization at point of focus is turned with reflection into its polarization direction (some degrees), s. fig. 17. As consequence the relation of the quantities of light as a function of the direction of rotation, which meet in both photo detectors, shifts.Bild 16

Bild 15
Bild 17

ATRAC Datenkompression

The MiniDisc can store only about 1/5 of the data due to the smaller dimensions CD. By the application particularly of the f high Wiedergabequalitt developed data compression system ATRAC is mlich storage of 74 min play time, with a quality, which does not differ practically hbar from that CD playback.
ATRAC been based on the utilization of scientifically secured psychoakustischer bases of the human Gehs and bertraegt only the audio signals, those of the ear for the correct perception of the respective sound signal to be also actually benigt [ 2 ].

Small Amplitudenauflung frt to Ouantisierungsrau. One ensures ever nevertheless daf, since this Quantisierungsgerusch remains unhbar, then the playback quality corresponds to that that CD therefore is a primary task with ATRAC to minimize the Hbarkeit of this noise by being hidden Ouantisierungsrau in frequency ranges, in which high signal levels occurs. The maximum of ear sensitivity is situated in the frequency area by 4 kHz, with other frequencies is partly substantially more insensitive the ear. A..tone, which is assumed with max. sensitivity even, is unhbar with same intensity, but other frequency. Basically two width unit of same intensity, but different frequency are unequally loud felt. A quiet sound can become unhbar with presence of a loud. This effect is defined as covering (masking) and is the more pronouncedly, the more near the width unit in its frequency together to be situated and the more grer their intensity difference is.
Within a temporally limited block ATRAC analyzes the music signal and determines the sensitivity of each frequency range. Sensitive areas are recorded very exactly with small quantization noise. Areas with smaller sensitivity are recorded fewer exactly, associated quantization noises remain unhbar, s.Bild to 18.

Bild 18

The frequency and time partitioning applied by ATRAC show fig. 19. The unequal width of the frequency bands is remarkable. This allocation is based on a further psychoakustischen effect, the groups of frequencies (Critical of tape), which with the human go were determined. The width of these groups increases with rising frequency, it amounts to e.g. with 100 cycles per second B=160Hz; with 1000 cycles per second B=160 cycles per second and with 10,000 cycles per second B = 2,500 cycles per second. The groups of frequencies are thus, like also fig. 18 show, in the lower frequency range substantially more closely together than with heren frequencies. The transfer of this allocation into the system ATRAC helps to achieve a high accuracy also with small transfer capacity.
Music signals constantly change, and the ear adapts its sensitivity the rate of these modifications. In lively passages e.g. ear sensitivity changes rapidly, in carried sections against it slowly. Therefore analyzes. ATRAC constantly in short time periods the input signal and adapts signal processing to the ear behavior. In lively passages Zeitblke are formed by 1,45 or 2,9 ms, in carried as far as 11.6 ms. Longer Zeitblke the ermlichen application of narrow frequency bands and results in high Frequenzauflung with high reproducible..tone quality (fig. 20). This signal-dependent Flexibilitt is a Schlsel f high effectiveness of the since tenkompression with simultaneous minimization of quantization noise. This unequal time and allocation of frequency are implemented with ATRAC by the combination of filters and Transfarmationsprozessen, s. fig. 20. The input signal is divided in three Bnder: low 0... 5.5 kHz, means 5.5... 11 kHz, highly 11... 22 kHz and with a modified discrete cosine transformation (MDCT) continues to process. Before it determined, whether the signal modification takes place rapidly or slowly, and accordingly the Zeitblke will become selected.
If the signal is divided into spectral regions, the MDCT values are divided according to the 52 unequal groups of frequencies. In these groups the bit rate reduction takes place in agreement to the masking and sensitivity conditions of each group. A special algorithm serves the avoidance of unnig high bit values. Thus the data item length will become kept small, at the same time however hbare modifications of the music avoided.
With the Rkwandlung of the signals in the decoder first the MDCT Frequenzwerte is erfrt into current values by inverse MDCT function. Schlielich are combined the three section tapes, in order to receive a normal digital 16-bit-Audiosignal. The real data stream betrgt 256 Kbit/s f the channelchannel channel.
The Komplexitt and the high level of these technological Lung become clear in the fact, since entire ATRAC signal processing is implemented already with Systemeinfrung in only one LSI.
Bild 20

Magnetooptic recording

MO technologies are already for some time in application. Specific demands f the application with the MiniDisc existed regarding the practically unlimited number of recording processes on a carrier and particularly in the implementation more easily and compact devices with low power requirement. Magnetooptic procedures record opto thermally magnetically. As storage media magnetic, amorphous Dnschichten from rare-earth metals (Godolinium, terbium, dysprosium) or alloys with these materials serves, evaporated on plastic carriers. A focused laser beam warms up after passing through of the transparent, optically effective carrier layer the magnetic layer tlich to the curie temperature of the respective material. Produces appropriate exterior magnetic field for the modulation which can be recorded at this. Place a domain with this direction of magnetization. After power-off of the magnetic field off or Abklen of the warmed up place of the layer on the environment parameters this is preserved, fig. 21. With application of the MO technique in the computer engineering the laser is controlled by the signals which can be recorded, the magnetic field fits continuously. These recordings are lchbar by the production of a continuous, uniform magnetization, either in their own run or by attachment of a second laser and magnet - similar as during the magnetic recording - before the recording heading.

Bild 21

Magnetic field modulation

F the development of the MD, with which the signals in the same format as with are to be stored that CD, were given three targets: Mlichkeit of the overwriting, memory density and track rate such as CD, address formatting already during the disk production.
The address formatting is gelt, as the Frungsrille is provided with deflections, which he implements the entire disk surface an absolute address with 13,3 ms Auflung (s. fig. 11).

The overwriting is a basic condition f the continuous recording already beforehand a disk recorded by audio signals in real time on. The application of the laser modulation, how it is used in optical memory of the computers, is not f the MD suitably, because the Lchen and recording take place here separately. Therefore f the recordable MiniDisc the magnetic field modulation was developed.

With the magnetic field modulation the laser is constantly switched on, and the magnetic field is modulated f the recording (fig. 22). The overwriting of available recordings through renouncement of a separate Lchvorgang permits. This technique stzt itself with the MD on a high-stable layer from terbium of ferrites cobalt, which a magnetization modification permits with comparatively low field strengths of 6,4 kA/m (80 Oe), so far was for instance the three-way value necessary. The complex request of the recording carrier are achieved among other things by the imbedding of the magnetic layer into a multi-layer system (fig. 6). The low field strength ermlicht a small solenoid actuator with small power requirement and practically immediate Flurichtungswechsel (approximately in 100 lv) when commutating the direction of magnetization.

Bild 22
Signal pit of the herkmlichen CD produced by an ionized argon laser with 460 Nm wavelength and focusing it a lens with WELL = 0,9. That results in a diameter of the light spot of 0,4 GM. F the system MD was only a diode laser with 780 Nm to the Verfung. Focuses it a lens with WELL = 0.45 arises a light spot diameter of 0,9 m. thereby appeared achieving memory density that CD first unmlich.

With experiments with D-RECORDING by means of conventional laser modulation (rate of 1.2 m/s) up to 200 faulted Datenblke per second were determined, a value the even still the request of the D-STANDARD corresponds. With application the number went to the magnetic field modulation on 20 per second zurk, fig. 23. Magnetic field modulation is thus not only f the erschreiben suitably, it results in also very error-poor recordings. The differences bezlich the error behavior between the laser and the magnetic field modulation find their assertion in the pit forms left really in the track. With the magnetic field modulation the diode laser produces constantly a performance of approximately 4.5 mW, and during focusing on the magnetic layer this achieves the curie temperature (about 180 c1. After leaving the light spot the temperature drops. When repeating this process with presence of a magnetic field with two different orientation directions dependent on orientation either 0 or 1 is recorded. Thus develop in the fig. 24 of pit shown. If the magnetic field can be switched sufficiently rapidly, then it is mlich, areas with a length of 0,3 pm also with a laser with 780 Nm wavelength, focuses it a lens with WELL = 0.45 to produce. Thus the demand is after one with that CD ereinstimmenden memory density erflt! Characteristically f the magnetic field modulation is in polarity switching (of + after -) begrdete the high symmetry of the pit structure. In contrast to it the laser modulation results in very asymmetrical structures.

Bild 23
The magnetic field can be oriented here only in a direction, with the allocation a 1 = laser lighting and 0 with switched off laser (unaufgezeichneter area), s. fig. 24. With laser modulation. e.g. the second half of a pit is always thicker, because the temperature rises. By controlling of the laser performance a balance would be mlich. On the other hand a different laser performance influences the at the beginning or terminator point of a pit. Thus distortions develop and erhte asymmetry. Simultaneously time error (jitter) occurs. That is particularly critical, because by the application of the EFM the length forms a tracing the basis of the data bearing for that of pit or that.
The magnetic field modulation does not permit fluctuations of the laser performance up to 20 %. the laser beam during the recording with magnetic field modulation only to f the heating up of the layer ensures there, is also a tilt between disk and scanning unit critical. Despite the described advantages the application in the computer engineering fails to the magnetic field modulation because of that lichen there high linear speed to more ber 10 m/s and the high frequencies (some 10 mc/s), with which the magnetic field are over polarized mte. In contrast to it with the MD necessary frequency is to be implemented heading constructions suitable by 720 kHz easily with:
Magnetic field modulation permitted only the one-sided data recording on the disk, f consumer's application is however no disadvantage, because a bilateral Ausfrung wde to more than the double cost.
Bild 24

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