Sony MDS-501 - Manual (Page 5)

What is the MiniDisc?
How MiniDiscs work How the MiniDisc got so smal
MiniDiscs (MD) come in two types: premastered
(prerecorded) and recordable (blank). Premastered ME)s,
recorded at music studios, can be played back almost
endlessly. However, they can't be recorded on or over like
cassette tapes. To record, you use a "recordable MD".
Premastered MDs
Premastered MDs are recorded and played like regular CDs.
A laser beam focuses on the pits in the surface of the MD and
reflects the data back to the lens in the recorder. The recorder
then decodes the signals and plays them back as music.
Recordable MDs
Recordable MDs, which use magneto-optical (MO)
technology, can be recorded again and again. The laser
inside the recorder applies heat to the MD, demagnetizing
the magnetic layer of the MD. (See illustration below.) The
recorder then applies a magnetic field to the layer. This
magnetic field corresponds exactly to the audio signals
generated by the connected source. (The north and south
polarities equate to digital "1" and "0".) The demagnetized
MD adopts the polarity of the magnetic field, resulting in a
recorded MD.
■ Recording Mechanism
The 2.5-inch MiniDisc, encased in a plastic cartridge that
looks like a 3.5-inch diskette (see illustration below), uses a
new digital audio compression technology called ATRAC
(Adaptive TRansform Acoustic Coding). To store more
sound in less space, ATRAC extracts and encodes only those
frequency components actually audible to the human ear.
■ Parts Making Up a MiniDisc
Shutter
Head Drive Signal
h I I_________
iH
n_____ □____
Recording Head
•fna: l-t-
Magnetic Field
Cross-Sectional View of
Recorded Pattern / A
Laser Beam
Move direction New Old
N ( s ( N ( S ( j ^ ) s ( N ( S ( n
Recorded Pattern
How quick random access and the TOC
(Table Of Contents) systems work
Like CDs, MDs offer instantaneous random access to the
beginning of any music track. Premastered MDs are
recorded with location addresses corresponding to each
music selection. Recordable MDs are manufactured with a
"User TOC Area" to contain the order of the music. The TCXT
system is similar to the "directory management system" of
floppy disks. In other words, starting and ending addresses
for all music tracks recorded on the disc are stored in this
area. This lets you randomly access the beginning of any
track as soon as you enter the track number (AMS), as well
as label the location with a track name as you would a file on
a diskette.