What is "Hi-MD"?Introduced by Sony in January 2004, Hi-MD is a nearly complete revamping of the original Minidisc system. The most significant change is the introduction of Hi-MD media, which includes a new 1GB blank in the existing MD form-factor and a reformatting of existing MD media that doubles its capacity to 305MB. In addition, several important and long wished-for Minidisc capabilities have been incorporated into Hi-MD equipment.
What new capabilities does Hi-MD equipment provide vs. the existing Minidisc?
What is Hi-MD media?There are two Hi-MD media formats: a new 1GB magneto-optical medium based upon DWDD ("Domain Wall Displacement Detection") technology, and the original Minidisc magneto-optical medium (60', 74' and 80') reformatted to double its capacity. The Sony 1GB Hi-MD disk is the first commercial use of DWDD technology (as of January, 2004).
What is "Domain Wall Displacement Detection" (DWDD)?Domain Wall Displacement Detection is one of a class of optical readout methods called Magnetic Super Resolution ("MSR"). MSR techniques address the fact that Magneto-optical systems can write much finer than they can read; magnetic domains ("bits") can be recorded on the disk that are smaller than the laser spot*, such domains cannot be read back directly since the laser spot will illuminate several domains at once.
DWDD Conceptual Diagram|
In DWDD, the recording medium is actually a 3 layer sandwich consisting of (from top to bottom) the displacement (aka readout) layer, the switching layer, and the memory layer. When the switching layer is heated to its Curie temperature (which is below the Curie temperatures of the memory and readout layers), it allows a small magnetic domain in the memory layer to appear larger than it really is in the readout layer.
The Magnetic Super Resolution technique was first discovered by Sony, and Sony has a DWDD patent that references 4 Canon patents. See Canon's DWDD explanation for further information.
[*Magneto-optical systems like Minidisc that use Magnetic Field Modulation are able to record domains smaller than the laser spot because they actually create crescent shaped regions that are magnetized as the recording layer cools below its Curie temperature. The size of these regions is determined by the switching rate of the signal sent to the magnetic head. See Sony's pictoral description of MO systems].
Is this like DVD technology then?No, it's completely different. DVD is an optical format, with closer tracks (0.74μm vs. 1.6μm), smaller pits (0.40μm vs 0.83μm), higher numerical aperature (0.6 vs 0.45), and shorter wavelength laser (640nm vs. 780nm) than CD/MD (MD uses the same optical parameters as CD). Hi-MD on the other hand is Magneto-Optical, using a laser to read and a magnet and a laser to write. In fact, Sony managed to create the Hi-MD system while holding to the original Minidisc's optical parameters, bringing the benefit of backward compatability and allowing them to manufacture Hi-MD equipment without a substantial change in cost structure. This means however, that pre-recorded 1GB Hi-MDs [that used CD Pit/Land recording] are not possible.
How did Sony increase capacity on the existing Minidisc to 305MB?
|Sony diagram from Hi-MD announcement
Photo courtesy AV Watch
Several changes were responsible for the increase in capacity:
What audio encodings and capacities exist on Hi-MD media?On Hi-MD media, these audio encodings can be created:
|Encoding Mode||Recording capacity(1)||Created by ...|
|305MB Hi-MD |
|1GB Hi-MD Media||recording with |
|downloading from PC|
to Hi-MD equipment
|Linear PCM 1.4mbps||28m||1h 34m||O yes||X no|
|ATRAC3plus 256kbps "Hi-SP"||2h 20m||7h 55m||O yes||O yes|
|ATRAC3plus 64kbps "Hi-LP"||10h 10m||34h||O yes||O yes|
|ATRAC3plus 48kbps||13h 30m||45h||X no||O yes|
|ATRAC3 132kbps "LP2"||4h 50m||16h 30m||X no||O yes|
|ATRAC3 105kbps||6h 10m||20h 50m||X no||O yes|
|ATRAC3 66kbps "LP4"||9h 50m||32h 50m||X no||O yes|
|ATRAC 292kbps "SP"||Not supported on Hi-MD media|
Note: (1)As stated in Sony literature
Is Hi-MD equipment compatible with original MD recordings?All Hi-MD equipment will play original Minidisc recordings (this is a requirement of Sony's Hi-MD licensees).
Can Hi-MD equipment record in the original Minidisc format?It depends upon the Hi-MD equipment, but it appears that all Hi-MD equipment introduced so far will record in all Hi-MD (PCM, Hi-SP, Hi-LP) and original-MD (SP, LP2, LP4) modes. Recordings made in the original-MD modes are only possible on std-MD disks formatted in the original (160MB) mode.
What happens if I try to play a Hi-MD formatted disk in a non-Hi-MD machine?A non-Hi-MD machine can read neither the 1GB Hi-MD media nor an original Minidisc reformatted in Hi-MD format. The result depends upon which of these two are used:
If I reformat an original Minidisc blank to Hi-MD format, can I later reformat it back to the original Minidisc format?Yes. Hi-MD formatting does not cause an irreversable change to the disk. Since a std-MD machine cannot read a Hi-MD reformatted disk (see above) you must first erase it (using "ERASE ALL"); it may them be used as a normal std-MD blank.
What happens if I try to record on a 1GB Hi-MD blank with a non-Hi-MD machine?The unit will report a read error and will not read/write on the Hi-MD disc.
What is the audio quality of ATRAC3plus?Updated: At Sony's Hi-MD annoucement they showed a chart depicting the relative standing of their ATRAC codecs. The diagonal lines indicate the audio quality equivalence of today's ATRAC3plus at 64kbps with the first version of ATRAC (ca. 1992) at 292kbps:
|Sony diagram from Hi-MD announcement
Photo courtesy AV Watch
The first generation ATRAC was a far cry from the quality of Type-R DSP for ATRAC introduced in 1998, and in fact it was probably similar in quality to MP3 at 128kbps. This view is supported by scientific listening experiments conducted on Sony's behalf by Intertek Testing Services (UK) and TESTFactory (Germany). Both reports showed a near equivalency of ATRAC3plus at 64kbps with MP3 at 128kbps:
|From ITS Test Report, showing near equivalency of
ATRAC3plus@64kbps and MP3@128kbps
If indeed ATRAC3plus at 64kbps is equivalent to MP3 at 128kbps this is good news for two reasons: 1) 1GB blanks will be able to hold 34 hours of audio equivalent to MP3@128k and 2) ATRAC3plus at 256kbps should be quite good, and quite likely better than original ATRAC at 292kbps.
Can I drag and drop ATRAC files between a Hi-MD system and a PC?No, SonicStage and SimpleBurner must be used to transfer audio between a PC and Minidisc.
How is audio uploading from Hi-MD to PC conducted?SonicStage (download) mediates all uploads from Minidisc to PC (or Macintosh, with Sony's MZ-M10 and MZ-M100 Hi-MD units). Conversion of uploaded audio to .wav format is done by SonicStage itself as of version 3.1. In prior versions audio may be converted to .wav file using Sony's Wave Conversion Tool (only for mic or line-in Hi-MD recordings) or using the MarcNet Hi-MD Renderer.
Hi-MD Flash website (Japanese) has this diagram (click to enlarge):
Will I be able to use Hi-MD to upload analog-source recordings made on existing ("std-MD") equipment?No. Sony has stated that only analog-source recordings created on Hi-MD equipment will be eligible for upload. (Discussion)
How fast will I be able to transfer music from my PC to an MD with SonicStage?Sony says that downloading can run at up to 100X realtime (assuming 48kbps audio content).
What are the technical specifications of the Hi-MD disks?Here are the specifications for the original Minidisc, its Hi-MD formatted version, the Hi-MD 1GB disk, and (for comparison) Sony's 650MB "MD-View" disk that was used in their Minidisc camcorder.
|Current MD format||Existing MD formatted into �Hi-MD�||Hi-MD 1GB Disc|| MD-View|
(from MD Discam)
|Magneto-Optical Recording Method||Magnetic Field Modulation||Magnetic Field Modulation||Domain Wall Displacement Detection||Magnetic Field Modulation on two layer medium (record layer and record assist layer)|
|Laser Wavelength (λ)||780nm||780nm||780nm||655nm|
|NA of Objective Lens||0.45||0.45||0.45||0.52|
|Thickness of Substrate||1.2mm||1.2mm||1.2mm||1.2mm (but with new substrate resin)|
|Tracking Format||Groove Recording||Groove Recording||Groove Recording||Groove Recording|
|Addressing||Wobbling Groove (ADIP)||Wobbling Groove (ADIP)||Wobbling Groove (ADIP)||Interlaced Wobbling Groove (ADIP with 1 address per track)|
|Data Detection||Bit by Bit||PRML||PRML||Bit by Bit|
|Shortest Mark Length||0.83μm||0.58μm||0.21μm|
|Data Transfer Rate||1.25Mbps @1.2m/s||4.37Mbps @2.4m/s||9.83Mbps @1.98m/s||9.4Mbps|
What websites have Hi-MD information?English:
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