RCI Minidisc Page
MDLP (``Long-Play'') Mode Topics
What is MDLP?
Minidisc Long Play. It's a new encoding method for audio on Minidisc that offers two
modes: one gives 160 minutes stereo ("LP2"), the second gives 320
minutes stereo ("LP4"). LP2 is stereo encoded (each channel is
independent), LP4 is joint-stereo (both channels are coded
simultaenously, see below).
What encoder is used for MDLP?
So called "ATRAC3", which is also used in the Sony MemoryStick
Walkmans, Vaio Music Clip and Network Walkman.
ATRAC3? Isn't that a step backwards? I thought modern Sony MD equipment was up to
ATRAC 4 or something.
Sony has chosen a confusing naming scheme for their variations of
ATRAC. All Minidisc equipment before the advent of MDLP used ATRAC1 of
some generation or another (note the lack of a space between
ATRAC and the number 1). We should really be calling the
ATRAC of the MZ-1 (Sony's very first MD machine) ATRAC1 version
1.0, for the MDS-501 (the first high-end MD deck) ATRAC1
version 2.0, etc. By this nomenclature, Sony's current MD decks
(ca. 2001) are using ATRAC1 version 4.5 and ATRAC1 Type
R. MDLP uses a new and incompatible encoding called ATRAC3
version 1.0, which we shorten to just ATRAC3 (note again the lack
of a space between ATRAC and the 3).
Oh that ATRAC3. Then what happened to ATRAC2?
It was renamed to ATRAC3! Seriously though, audio coders are evolving
computer programs with few natural dividing lines between them, though
perhaps it's fair to rename them when their stored formats become
incompatible. ATRAC2 (described briefly and in slightly more detail) differs
substantially from the original, existing ATRAC system, having twice
the transform window size (1024 samples [23.2ms], vs. 512 samples
[11.6ms]), encoding tone components separately from other spectra,
splitting the input signal into 4 bands instead of 3, and using
Huffman coding on the final bit stream to squeeze out redundancy.
ATRAC2 was apparently never incorporated into a product.
ATRAC3 (as described briefly by Sony's ATRAC3 information page and in more detail by
a TechnoWorld article (PDF)) appears
quite similar to ATRAC2 in structure. The only difference is that
ATRAC3 again uses the original ATRAC's QMF (Quadrature Mirror Filters)
for band splitting, whereas ATRAC2 used PQF (Polyphase Quadrature
Filters). Given the popularity of MP3, and the fact that
there was no existing ATRAC2 format to be incompatible with, it seems
plausible that marketing arguments, as much as anything else,
convinced Sony to rename their high compression codec
Can the new LP mode tracks be played back on old, non-MDLP hardware?
What happens when I try to play an LP track on old, non-MDLP hardware?
The track is played as silence. A 20 min. LP2 track is played as 10
min. silence. A 20 min. LP4 track is played as 10 min. silence
(because the MD unit thinks it's playing an SP mono track).
The non-LP machine's display of the track name is also likely to show
the characters "LP:" at the beginning of the title. These characters
are put there by MDLP recorders in their factory default setting (this
feature, called "LPstamp", can be disabled). MDLP machines will also
strip off the initial "LP:" (if LPstamp is enabled) when displaying LP
Will the new MDLP units play back old ("SP" mode) discs?
Will the new MDLP units record "old" (SP mode) tracks?
Can old non-MDLP units title MDLP tracks?
What bitrates are used?
Standard ATRAC ("SP") is 292kbps, LP2 is ~132kbps, LP4 is ~66kbps. The
LP mode bitrates are not simply 146kbps (292/2) and 73kbps (292/4) for
this reason: In LP2 and LP4 modes 20 bytes of dummy data per 212 byte
soundgroup are used to keep compatibility with SP mode, making them
appear as normal ATRAC soundgroups containing silence. This allows
LP2/4 tracks to play as silence on non-MDLP equipment. The intention
is that older MD units should not produce random digital noise when
playing LP tracks.
You mean that 10% of an MD's capacity is
wasted in LP mode due to lack of planning!?
Yes. Sony defined a 2 bit field in the original MD specification to
indicate non-standard track codings, allowing players to ignore
unknown track types (see the MDLP-mode bit in the fragment
headers). Unfortunately, non-MDLP units seem rather to ignore the
mode bits and will try to play the MDLP audio anyway.
Why aren't there LP monoaural modes that double the recording time?
ATRAC3 in LP4 mode encodes audio in "joint-stereo" mode, encoding
the left and right channels in one step (i.e. jointly) and
exploiting the similarity between channels to increase
compression. Because of this, the capacity increase when encoding a
mono signal is not 2:1, but somewhat less. This, and the added
complexity of a fractional increase in capacity, apparently
disuaded Sony from providing a mono LP4 mode. ATRAC3 in LP2 mode on
the other hand could be used to offer double playing time
mono, but Sony's current machines do not offer it.
If LP4 mode's left and right channels are coded jointly, then what kind of channel separation does it have?
Unknown, but coding two completely unrelated signals on the left and
right channels will not give spectacular results.
How high quality is the LP mode audio?
LP2 mode is reportedly quite close to standard ATRAC. LP4 mode has noticeable
artifacts, but is still suitable for portable applications.
Brian Youn has assembled some user comments
on MDLP mode's quality. There are also comments in the Sony MZ-R900 equipment
Will an MDS-W1 move LP mode tracks?
The Sony MDS-W1
double MD deck will not move LP mode tracks properly. When the MDS-W1
moves LP2 and LP4 tracks to another disc it sets their SP bits on in
the UTOC track header, turning LP4 tracks into (silent) SP mono and
LP2 tracks into (silent) SP stereo. The track's audio data is copied
properly however, so with careful use of TOC cloning to restore the LP
bit in the track header, copied LP tracks will play correctly.
What MD equipment supports LP mode?
See T's MDLP Equipment Table.
How can I try out ATRAC3 and listen to some samples?
Windows users can
download this ATRAC3.zip file,
unpack it into a new folder, then right click on the
atrac3.inf file and choose "Install". This loads an ATRAC3
codec (.acm file) into the system so that .wav files containing
ATRAC3 audio can be played (and recorded!) with your normal system tools (Sound Recorder,
Windows Media Player 7, Winamp, Goldwave [encode ATRAC3 in Goldwave by selecting
"File->Save As->Save as type: 'Wave', File Attributes: 'ATRAC3'"]). PlanetMG, a website that offers ATRAC3 and Windows
Media audio files for download, also lets you download an ATRAC3 plugin for the Windows Media Player. RealPlayer's "RealAudio 8" supports Sony's ATRAC3 format as well.
After loading you can listen to the following audio snippet of
"Sichia". The example was intentionally chosen from difficult
material, in order to highlight the audio quality differences at
- There are publicly available ATRAC3 files on the Web, however
Sony is now using a custom format instead of WAV format;
the header is incompatible with WAV so those files cannot be directly played
with standard sound tools. However, the data is the same, all that's needed
to make one work with the other is to replace one header with the other.
- This audio codec was assembled from publicly available bits
on the Web and hence may not represent the ATRAC3 codec Sony currently
supplies with their MDLP and MemoryStick audio devices. It is
supplied for educational purposes only, please address all questions
about commercial use and licensing of ATRAC3 to atrac3@Sony.co.jp.
Where can I learn more about ATRAC3?
Have a look at these links
What happens if MD hardware is made to play MD audio data in the wrong mode?
Using TOC cloning techniques, tracks recorded in one mode can have
their UTOC bits changed to allow them to masquerade as audio data of a
different mode (see the track mode
bit assignments in the UTOC). David Tamkin has kindly conducted
experiments that allowed him to produce this table:
|Mode of Recorded Audio Data ||Mode for Track Indicated in UTOC ||Result when played on MDLP unit ||Result when played on non-MDLP unit
|SP stereo ||SP stereo || SP stereo || SP stereo|
|SP mono || half-speed SP mono|| half-speed SP mono|
|LP2 || silent || SP stereo|
|LP4 || silent || half-speed SP mono|
|SP mono ||SP stereo || double-speed SP mono || double-speed SP mono|
|SP mono || SP mono || SP mono|
|LP2 || silent || double-speed SP mono|
|LP4 || silent || SP mono|
|LP2 || SP stereo || silent || silent|
| SP mono || silent || silent|
| LP2 || LP2 || silent|
| LP4 || nonstop squeal ||silent|
|LP4 || SP stereo || silent || silent|
|SP mono || silent || silent|
| LP2 || double-speed LP4 ||silent|
| LP4 || LP4 || silent|
Are there translations of the MDLP section of the FAQ?
Yes, there is a full translation of the MDLP FAQ in Japanese.
This file can be found at http://www.minidisc.org/minidisc_faq.html
As always, I would be much obliged for any updates and corrections
from Sony Engineering. -Eric
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