Sony MZ-B50 User Manual download pdf (Page 41)

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What is an MD?

How MiniDisc works

MiniDisc (MD) comes in two types:

premastered (prerecorded) and recordable

(blank). Premastered MDs, 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

must 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 information 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. 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.

How the MiniDisc got so small

The 2.5-inch MiniDisc, encased in a plastic

cartridge that looks like a 3.5-inch diskette

(see illustration on the left column), 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.

Quick Random Access

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 TOC (Table of Contents) 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.

User TOC Area

Music Data

Contains the order and start/end

points of the music.

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 135 136

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