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Two types of minidisc
There are two types of minidisc, “recordable MDs” and “playback-
only MDs.” The playback method for each is the same: a laser irra-
diates the disc and the signal is read from the beam which comes
back. However, the recording method for each type is different.
Playback-only MD
This is the type used for commercially-available pre-recorded MDs,
on which recording cannot be done. Like a CD, data is recorded
based on the presence or absence of small indentations called pits.
A disc recorded with this format is called an “optical disc.”
Recordable MDs
These are the so-called “blank” MDs you can use to make your own
recordings. Data is recorded by magnetism, which is easily proc-
essed, so that recording can be done again and again. By using a la-
ser to heat the disc, the magnetism is erased and the magnetic head
records the new data. Discs with this type of recording method are
called magneto-optical (MO) discs.
ATRAC (Adaptive Transform Acous-
tic Coding)
Within recordings, there are sounds which cannot be readily heard.
For example, as the volume decreases, high-pitched sounds and
low-pitched sounds become difficult to hear. also, if a quiet sound
comes at the same time as or just after a loud sound, it will not be
heard. With minidiscs, data is compressed using a technology called
ATRAC (Adaptive Transform Acoustic Coding) which selectively
chooses sounds based on human sense of hearing characteristics.
With this technology, the recorded data is about one-fifth the vol-
ume of the original data, allowing it to fit on a compact minidisc.
Sound skip guard memory
With the minidisc, the data of the track being played can be tempo-
rarily stored up using a function called “sound skip guard memory”.
Even when data cannot be collected properly from the disc due to
shaking or vibrations, information is stored in the “sound skip guard
memory”, so that there is no break in the sound which is actually de-
livered.
SOUND
0
+20
-20
-40
-60
(dB)
20 50 100 500 1k
5k 15k10k
(Hz)
Low
|
Sound range
\
High
Sound range and sensitivity of our ears
Sharp
»
Sensitivity
of our ears
«
Dull
STOP
Optical pickup
Sound jump
guard menory
During normal play When vibration has occurred
UTOC (User Table Of Contents)
In a minidisc, apart from the recorded tracks, there is the “UTOC”. In this area, information such as the position where each track is recorded,
the track divisions, and track order are listed. When music search is done, the UTOC is consulted, and the tracks are quickly found and played
back. When editing is done, only the UTOC is changed, so there is no need to re-record the tracks.
■■
MD Messages
Messsage Meaning Action
BLANK DISC
A disc has been inserted with nothing
recorded on it.
Except when making a new recording,
replace the disc with one which has been
recorded on.
UTOC
Track details
Contents
1. Track A: Page 9
2. Track B: Page 6
3. Track C: Page 10
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RD-MD5(B)-e.fm Page 23 Wednesday, December 2, 1998 11:40 AM