34-
GB
User TOC Area
Music Data
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 above), 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.
Shock-Resistant Memory
One major drawback of optical read
systems is that they can skip or mute
when subjected to vibration. The MD
system resolves this problem by using a
buffer memory that stores audio data.
Contains the order and start/end
points of the music.
