Minidisc uses an audio compression codec called ATRAC (Adaptive TRansform Acoustic Coding) to fit more audio in less data space. Pressed minidiscs use traditional CD technology, but in a smaller size. Blank media uses Magneto Optical technology.

MiniDisc overview by Tadao Yoshida, October 1994: IEEE overview

ATRAC overview, October 1992: AES overview

Excellent French article covering ATRAC1 - ATRAC3

Up through 1997, Sony made improvements to the ATRAC codec used by minidisc each year, and each successive hardware generation records and plays sound more accurately.

Collectively the “standard play” ATRAC codecs are known as ATRAC1.

1998's improvement to ATRAC1 was marketed as Type-R and was available initially in stationary recording decks such as the MDS-JE630.

In 2000, Sony introduced ATRAC3, a new set of modes to enable MDLP. Most MDLP machines have Type-R, but not all Type-R machines are MDLP. Type-R's specific improvements to recording only apply to the SP and mono recording modes. 1) All NetMD machines, even portables, have Type-R or newer recording.

In 2002 Sony introduced a new set of improvements marketed as Type-S. Type-S itself is primarily an improvement to MDLP playback. All MDLP recordings should benefit from being played back on a Type-S machine. Type-S has no additional recording improvements, but all Type-S recorders include the Type-R recording and encoding improvements.

A Magneto-Optical Disc is an Optical Disc technology that allows data to be written to a disc by a magnet head once the disc has been heated up to its curie point, typically done by a laser. After this process the disc can be read by a laser in a similar way to most modern optical discs. This technology was used for the MiniDisc format and allowed MiniDiscs to be rewritable well before CD-RWs entered the market. It's worth noting that the Orange Book Standard for Compact Discs does have a standard for CD-MO, which would have been a rewritable Magneto-Optical CD, however the standard was never used in a commercial product. 2)

MDLP is a way of extending the amount of music that is stored on a single MiniDisc - on an 80 min disc in SP (standard play), you can store 160 minutes in LP2 and 320 minutes in LP4 (note that this is Joint Stereo, where left and right channels are smushed together - Ed: this statement is not correct, sum and difference encoding is used and that works best where the two channels contain a lot of similar material as is the case with much popular music)

Due to the way MDLP stores the music, an LP2 or LP4 encoded track will play back as silence on a machine that doesn't support MDLP.

A mix of SP, LP2 and LP4 may be recorded on the same disc. Note that if you're recording a lot of tunes in LP4, you may run out of characters while naming tracks (1785 characters total, max)

Announced in mid-2001 and first introduced on the Sony MZ-N1 portable recorder in December of the same year, NetMD is an extension to the Minidisc format that allows direct transfers of compressed, ATRAC audio from a PC to Minidisc via USB interface. Audio transfers can be conducted at rates considerably faster than real time (up to 64x for LP4 audio on certain units).

When NetMD was first introduced, it included a frustrating “Check In/Out” system via the OpenMG and SonicStage software, which prevented you sending the same song to more than 3 MiniDiscs until a Check-In had wiped the track from one of those three discs. This has since been abandoned, likely due to the fact that you can't bring data from a standard NetMD back to a PC without re-recording it (Hi-MD can do this).

In 2004, Sony introduced Hi-MD, which could play all of the existing minidisc formats and introduced the ATRAC3plus codecs for higher quality and more flexibility. Hi-MD also introduced a new disc format oriented around a typical FAT filesystem, and the machines can play and record Linear PCM. Hi-MD added a new 1GB disc type, and can format an existing 60/74/80-minute minidisc to the Hi-MD format, which gets more space on the disc. Later generation Hi-MD recorders can also play MP3 files, however all of the files must be uploaded using Sony's software or modern transfer software.

The Hi-MD recording modes for Hi-MD-formatted discs are:

  • Linear PCM 1411 kbps
  • ATRAC3plus Hi-SP 256kbps
  • ATRAC3plus Hi-LP 64kbps
  • ATRAC3plus 48kbps
  • ATRAC3 132kbps “LP2”
  • ATRAC3 105kbps
  • ATRAC3 66kbps “LP4”

The known MDLP recorders without Type-R are primarily portables: MZ-R500, MZ-R700, MZ-R900, and variants such as the MZ-G750.
Upgrading and repairing PCs By Scott Mueller, page 739: “The Orange Book comes in three parts: Part I describes a format called CD-MO (magneto-optical), which was to be a rewritable format but was withdrawn before any products really came to market”
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