Minidisc FAQ: Hi-MD Topics

January 2004

  1. 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.

  2. What new capabilities does Hi-MD equipment provide vs. the existing Minidisc?

  3. 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).

  4. 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
    (Courtesy Canon)

    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].

  5. 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.

  6. 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:

    1. The way data bits are encoded into bits on the disk (the modulation system) was changed from EFM ("Eight to Fourteen Modulation", the Compact Disc's method) to the more efficient RLL1,7 (typical of hard drives).
    2. The readout electronics were changed from a simple peak detector to a more sophisticated Partial Response Maximum Likelihood ("PRML") system that essentially uses digital signal processing techniques to extract the disk data signal from inter-symbol noise, allowing bits to be packed closer together.
    3. The error correction system and "sector structure" were changed to increase data packing efficiency to 80% (Sony doesn't mention what these changes were however).
    Changes #1 and #2 brought a factor of 1.38x, #3 brought 1.48x, for a total of 2.04x.

  7. 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
    formatted Minidisc
    1GB Hi-MD Mediarecording with
    Hi-MD equipment
    downloading from PC
    to Hi-MD equipment
    Linear PCM 1.4mbps 28m 1h 34m O yesX no 
    ATRAC3plus 256kbps "Hi-SP" 2h 20m 7h 55m O yesO yes
    ATRAC3plus 64kbps "Hi-LP" 10h 10m 34h O yesO 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

    For calculating available Hi-MD capacity when using a mix of recording modes, Peter Ravn has made a Javascript-based Hi-MD space planning calculator.

  8. 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).

  9. 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.

  10. 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:
    1. If a 1GB Hi-MD is inserted, a std-MD unit will report a disc read-error.
    2. If std-MD media reformatted to Hi-MD is inserted, a std-MD unit will display "Hi-MD Disc" as the disk title. It will show two tracks, both tracks are named "Hi-MD Disc" with track-1 in mono, track-2 in LP4. Neither track will play (there is silence and the time counter doesn't show anything). The disk always shows no free space regardless of how much space is really available when used on a Hi-MD machine.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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):

  16. 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)

  17. 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).

  18. 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)
    Data Capacity 177MB 305MB 1.0GB 650MB
    Magneto-Optical Recording MethodMagnetic Field ModulationMagnetic Field Modulation Domain Wall Displacement DetectionMagnetic 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
    Diameter 64.8mm 64.8mm 64.8mm 64.8mm
    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 Modulation EFM 1-7RLL 1-7RLL 1-7RLL
    Data Detection Bit by Bit PRML PRML Bit by Bit
    Bit Length 0.59μm 0.44μm 0.16μm 0.34μm
    Shortest Mark Length 0.83μm 0.58μm 0.21μm
    Track Pitch 1.5μm 1.5μm 1.25μm 0.95μm
    Data Transfer Rate 1.25Mbps @1.2m/s 4.37Mbps @2.4m/s 9.83Mbps @1.98m/s 9.4Mbps

  19. What websites have Hi-MD information?

    English: Japanese: Dutch: French:


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As always, I would be much obliged for any updates and corrections from Sony Engineering. -Eric Woudenberg

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