Information on MDs Minidiscs | JVC RM-RXUV9RMD manual

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■Information on MDs (Minidiscs)

This is a new digital audio disc format: it has a diameter of 64 mm and enables up to 80 minutes of playback and recording.

The cartridge

The diameter of the disc itself is 64 mm, smaller than a CD single. The disc sits inside a 68 ✕ 72 mm cartridge, which also being pocket size, makes minidiscs extremely handy for carrying and storage. Since the disc is protected by the cartridge, dust and dirt cannot eas- ily get into it. And thanks to a shutter which is closed at all times except during use, there is no need to worry about scratches or fin- ger marks, making the handling of minidiscs very simple.

Cartridge

Disc

Shutter

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.”

SOUND

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.

(dB)

Sharp	+20
	0

È
	-20
Sensitivity
of our ears	-40
Ç
	-60
Dull

	20	50	100	500	1k	5k	10k	15k
								(Hz)
	Low Sound range \ High

Sound range and sensitivity of our ears

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.

Optical pickup

STOP

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 re- corded, 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.

UTOC

Contents

1. Track A: Page 9 Track details 2. Track B: Page 6

3. Track C: Page 10