What is MDLP?Minidisc "Long Play". Introduced in September 2000 on the Sony MDS-JB940 deck, it is 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 simultaneously, 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, and of 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.
Though ATRAC2 was never incorporated into an exported Sony product, the Sony PlanetMG FAQ states "a second format, called ATRAC Data, is used by Sony in a digital music distribution system offered via the SkyPerfecTV satellite service in Japan". This "ATRAC Data" is most likely ATRAC2, however Sony's MDS-DL1 and SkyPerfectTV press release makes no mention of "ATRAC Data", and certainly any audio stored on a Minidisc would have to conform to existing ATRAC standards for Minidisc.
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 ATRAC3.
What is ATRAC3plus?ATRAC3plus is a new audio codec from Sony that differs substantially from ATRAC3 (ATRAC4 would in fact have been a better name). Though not used in the original Minidisc, ATRAC3plus is used in Hi-MD and Sony's solid-state and CD walkman products. It uses a transform window 4 times bigger than ATRAC3 (4096 samples, or 92ms) and splits the input into 16 sub-bands prior to the FFT (MDCT) and subsequent bit allocation processing.
Sony has measured ATRAC3plus fidelity at 64kbps and found its audio quality equivalent to 128kbps MP3 (mech. trans.) Sony's current PC software produces ATRAC3plus output at user selectable bitrates of 132, 105, 66, 64 and 48 kbps. AV Watch Japan has done a bit of ATRAC3plus signal analysis and comparison with ATRAC3 (mech. trans.) ATRAC3plus is described briefly on Sony's ATRAC3 site (local copy).
Can the new LP mode tracks be played back on old, non-MDLP hardware?No.
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 track names.
Will the new MDLP units play back old ("SP" mode) discs?Yes.
Will the new MDLP units record "old" (SP mode) tracks?Yes.
Can old non-MDLP units title MDLP tracks?Yes.
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 monaural 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?Sony has not given channel separation specs for LP4 mode, 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 browser entry.
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.
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 various bitrates.
|Sample: "Sichia" (de Lucia) track 4, 2:00-2:35|
CD: Passion Grace and Fire (McLaughlin, Di Meola, de Lucia)
|Original CD audio||6MB|
|ATRAC3 @ 132kbps||580KB|
|ATRAC3 @ 105kbps||460KB|
|ATRAC3 @ 66kbps||290KB|
|MP3 Stereo @ 56kbps/24khz||245KB|
|MP3 Stereo @ 56kbps/22khz||246KB|
|MP3 Stereo @ 56kbps/16khz||244KB|
What about the ATRAC3 that Real Networks Supports?Sony and Real Networks negotiated a deal in which Real adopted ATRAC3 for their RealAudio8 wideband audio coder. The freely downloadable RealSystem Producer Basic (available for Linux, Mac and PC) can encode ATRAC3 audio at 352, 264, 176, 132, 105, 96, 64, 44, 32 and 20kbps. The 146kbps ATRAC3 rate is apparently only available with the $200 RealSystem Producer Plus package.
Getting the PC version of RealProducer to encode at these rates is a bit tricky, since the PC GUI is neither convenient nor obvious. Here are the steps:
It initially displays a "New Session" dialog box, asking for the name of the .wav file you wish to convert, and the name of the target ".rm" file you wish to create; browse to these or fill them in.
Here, the bitrate is selected in an indirect fashion through the "Target Audience" checkbox. This checkbox is intended for you to specify the sort of network bandwidth your audience will have. What it does is select ATRAC3 bitrate of the file you will encode.
This leads you to the Target Audience Settings dialog:
in which you can set your preferred ATRAC3 bitrate for each of the possible network speeds. However, with the "basic" version of the program, you are not allowed to change anything in this dialog box. It is only useful for selecting different target audiences and then seeing what ATRAC3 bitrate each corresponds to. When encoding Stereo Music, the correspondences are as follows (we include here the "Sichia" clip mentioned above, encoded at each bitrate for comparison):
|512K DSL/Cable Modem||352Kbps Stereo Music||[email protected]|
|384K DSL/Cable Modem||264Kbps Stereo Music||[email protected]|
|256K DSL/Cable Modem||132Kbps Stereo Music||[email protected]|
|Corporate LAN||105Kbps Stereo Music||[email protected]|
|Dual ISDN||44Kbps Stereo Music||[email protected]|
|Single ISDN||20Kbps Stereo Music||[email protected]|
|56K Modem||20Kbps Stereo Music||[email protected]|
Where can I learn more about ATRAC3?Have a look at these links
(ATRAC3 Block Diagram)
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|
|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|
Are there translations of the MDLP section of the FAQ?Yes, there is a full translation of the MDLP FAQ in Japanese.
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