Tascam MD-801R/P Mk II - Manual (Page 7)

TASCAM MD-801R/P Mk II
1–1
1 - Introduction
This manual covers the two models of the MD-801
Mk II product line: the MD-801R Mk II, which is
capable of recording and playing back on MiniDisc
media, and the MD-801P Mk II, which is for play-
back only of such media. Apart from the recording
and associated facilities provided on the MD-801R,
the functionality and specifications of the two units
are identical. For brevity, the unit will be referred to
as the “MD-801” in instances where there is no dif-
ference between the recording and playback models.
When a section of this manual describes a function
which is included as part of the MD-801R only, the
section will be marked as below:
3.12.2Laser pickup time
This indicates how long…
There are no features which are unique to the MD-
801P model.
1.1 About the MiniDisc format
This section provides some basic information regard-
ing the MiniDisc format. If more detailed informa-
tion is required, the reader is referred to one of the
many books on the subject. John Wilkinson,
The Art
of Digital Audio 2nd ed. Oxford: Focal Press, 1994 is
an excellent reference source, particularly Chapter
12, which deals with the use of optical discs in audio
applications.
The MiniDisc format (MD) is a convenient form of
digital audio media, using optical playback, similar
to CDs.
The format of the MD is substantially smaller than
that of the CD, and the disc itself is housed in a car-
tridge with a shutter, similar to that of a 3.5” floppy
disc drive. The disc platter should never be removed
from this cartridge.
Pre-recorded MDs, which are manufactured in the
same way as commercial CDs, using a stamper pro-
cess, are read using a laser beam to read the pits
stamped onto the disc.
Recordable MDs are also available, and the technol-
ogy used for recording on a recordable MD is
magento-optical, allowing the disc to be re-used
many times. Shutters on both sides of the disc allow
access to the disc surface by the recorder’s laser and
magnetic head.
There is a third kind of MD, the hybrid, which con-
tains pre-recorded pits at the center of the MD,
together with an area reserved for user recording.
Full explanations of the principles of magneto-opti-
cal recording may be found in a number of excellent
reference works, but briefly, during the recording
process, the disc is exposed to a strong laser beam
which heats the disc’s magnetic medium so that a
magnetic field can be applied to change the orienta-
tion of the magnetic particles. On cooling, this orien-
tation is permanently fixed, unless the disc is
reheated and re-recorded.
The MD format therefore provides the convenience
and durability of an optical disc format with the reus-
abilty characteristics of tape.
1.1.1 ATRAC compression
If a MiniDisc were to be recorded using exactly the
same techniques as a CD, the playback time would
be only 15 minutes of stereo playback.
However, using a technique known as ATRAC
(Adaptive TRansform Acoustic Coding), 74 minutes
of stereo audio at 44.1 kHz sampling frequency with
a 16-bit word length can be recorded on an MD.
ATRAC uses two important pyscho-acoustic princi-
ples to reduce the size of the recorded data: the
greater sensitivity of the human ear to mid-range sig-
nals, relative to bass and treble signals, and the
“masking” effect, whereby quieter signals are hidden
by louder ones.
The ATRAC used in the MD-801R/P Mk II is a very
recent version of this encoding scheme (4.5), result-
ing in an almost inaudible loss of signal quality.
1.1.2 Buffer memory
The ATRAC compression scheme has an additional
advantage, as a RAM buffer must be provided for the
compressed data, before it is decoded and sent to the
D/A converters.
On the MD-801R/P Mk II, this buffer memory holds
about 10 seconds’ worth of data. The advantage is
that, unlike a CD player, the MD-801R/P Mk II is not
vulnerable to mechanical shocks and vibration, etc.,
which can cause a CD player playback pickup to
jump and cause audible skipping.
1.1.3 Random access and U-TOC
The format of a recordable MD is much closer to that
of a computer disc than of conventional audio media.
The random access nature of the disc media allows a
logical “track” to be composed of sections of audio
data recorded at different points on the disc.
In the same way that a computer’s operating system
hides the details of the way that data is stored on the
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