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By P Jalvinger 970403 Last update 2000-01-11  This is the printable version. Get the normal version. It will take a few seconds.
To view the page correctly you should have the Verdana font installed. Rightclick, save as, go to the FONTS directory and save. Before you start
Welcome to my webpage about the MiniDisc. Before you start I have to tell you how the links are working in the text. You find a word, let's say
Curie and wanna have more information, just click on it. When you are done, just klick back (the one that
belong to the word) and just like that, you are back at the same place where you came from, piece of cake don't you think! Enjoy...
The MiniDisc (MD) is the latest sound media created by Sony. It uses a small disc protected in a
cartridge (72* 68* 5 mm) which is
digital recordable up to a million times. A MiniDisc has a playtime of 74 min (148 min mono) with almost the same quality as a CD. With the 4th generation MD's (ATRAC 4.0)
you can't tell the difference. I have a Sony MDS-JE500 myself, so belive me when I say that I have tested the machine as much as possible.
If you are tired of some tracks, simply delete them with a few button pushes and record new ones, placing them in any order you like.
It sounds to good to be true, but it is really that simple to use the editor.
The creation of the MiniDisc system began in 1986, it was developed to meet the increasing demand for a portable recordable
high-quality digital audio media. This required the refinment of several technologies. Formats have been used simultaneously, exploiting the strengths of each
medium. Since the introduction of the compact disc, the "dual-format" has, for the most part, consisted of the CD and the analog cassette tape. CD provides superior
audio reproduction, while cassette is recordable. As a portable medium, neither is ideal. MD was introduced as the next step in this evolution. MD combines the strengths
of both CD and cassette into a single format. Designed to be durable, reliable and virtually unaffected by external magnetic fields, it retains its high quality despite repeated recording and playback.
A single MD holds the same amount of music at the same sampling frequency as a CD (74 min and 44,1 kHz) but does so in 1/5 as many bits by using
a compressing method Sony calls
ATRAC (Adaptive TRansform Acoustic Coding). ATRAC is a form of data reduction technique that attempts to encode only the information audible
to the human perceptual system. The input signal is divided into three subbands
which are then transformed into the frequency domain using a variable block length. Transform coefficients are grouped into nonuniform bands to reflect the
human auditory system, and then quantized on the basis of dynamic sensitivity and masking characteristics.
ATRAC is also the basis of Sony's SDDS cinema digital audio system.
back
Masking occurs when one sound is rendered inaudible by another. Simultaneous masking occurs when the two sounds occur
at the same time, such as when a conversation (the masked signal) is rendered inaudible by a passing train (the masker). Backward masking occurs when the
masked signal ends before the masker begins, forward masking occurs when the masked signal begins after the masker ended. Masking becomes stronger
as the two sounds get closer together in both time and frequency. For example, simultaneous masking is stronger than either forward or backward masking
because the sounds occur at the same time. Masking experiments are generally performed by using a narrow band of white noise at the masking signal, and
measuring the just-audible level of pure tone at various times and frequencies.
back
Critical bands arose from the idea that the ear analyzes the audible frequency range using a set of subbands. The frequencies within a critical band are
similar in terms of the ear's perception, and are processed separately from other critical bands. Critical bands arose naturally from experiments in
human hearing and can also be derived from the distribution of sensory cells in the innerear. The sensitivity of the ear varies with frequency, critical bands are
much narrower at lower than at higher frequencies. The ear is most sensitive to frequencies in the neighbourhood of 4 kHz. Soundpressurelevels
which are just detectable at 4 kHz are not detectable at other frequencies. In general, two tones of equal power but different frequency will not sound equally loud.
Recordable MiniDiscs use a variation on conventional magneto- optical methods that Sony calls "Magnetic Field Modulation", in which
data is recorded using a semiconductor laser at high power together with a magnetic head. As the disc sweeps past the laser, a tiny area on the MD's
magnetic recording layer (Terbium, Iron and Cobolt) is heated to its
Curie temperature of 180°C while the
field of the magnetic head
is in contact with the other side of the disc switched back and forth to write a data pattern. When the area the head has magnetized moves away from the laserspot
, it cools below the Curie point to become "cast" in a string of N and S magnetized regions on the disc, spaced 30 millionths of a centimeter
apart, and corresponding to the stream of bits being recorded. Playback is accomplished using the same laser at a lower power, taking advantage of the
Kerr effect, in which the polarization angle of the reflected laser light is affected by whether it was reflected from an N or S magnetized region. The MD
optics detect these polarization differences to reconstruct the recorded bit stream.
The biggest problem in using optical discs in portable applications has been that of skipping due to shock or vibration. With MD, this is dramatically minimized
by using a semiconductor memory. The memory acts as a buffer, holding digital data equivalent to about three seconds of playing time before it's sent for
conversion into analog signals for playback. If the player is exposed to shock or sudden movement, jarring the pickup from its position on the disc, the
memory, which is unaffected by shock or movement, will continue to output digital data to maintain playback. Since the pickup's position is constantly monitored, it
can quickly continue tracking. Efficient operation of the shock-resistant memory is enabled using digital data compression. The pickup reads data from
the disc at the rate of 1.4 Mbit/second, but playback requires a rate of only 0.3 Mbit/second because the ATRAC system uses only about 1/5th of the
amount of data normally required. If the pickup loses its position, and the flow of data into memory is interrupted, data continues to flow from the
memory at a rate of 0.3 Mbit/second, enabling playback to continue from 3 to 10 seconds (vary from player to player, new players have up to 40 seconds of shockmemory). When the pickup resumes its position, it reads data from the
disc at 1.4 Mbit/second, replenishing the memory's data in less than a second.
back
A system developed to limit digital dubbing to first generation copies only. Digital dubbing from a digital copy is not possible.
However it's possible to make an analogue dubbing of the digital MD, and with that analogue MD you can make a new digital dubbing and so on.
But how does the system knows what generation it is and if it's a digital recording, well here's how it works.
Major specifications
ANALOGUE DIGITAL
ADIP - ADdress In Pre-groove
ATRAC - Adaptive TRansform Acoustic Coding
CIRC - Cross Interleave Reed-Solomon Code
Cluster
CLV - Constant Linear Velocity
Curie Temperature
EFM - Eight to Fourteen Modulation
Lead-in Area
Link Sector
Magnetic Field Modulation
Masking Effect
MDCT - Modified Discrete Cosine Transform
Pre-groove
Program Area
Sampling Frequency
Sampling Rate Converter
SCMS - Serial Copy Management System
TOC - Table Of Contents
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