So I was watching the excellent Techmoan YouTube channel the other day and as he discussed various interesting but now-dead technologies it got me thinking of one that I actually had owned: MiniDisc.

What’s a MiniDisc?

If you happen to not know or remember the MiniDisc I’m not surprised. While it did have a bit of a splash in the early ’90s and then again in the early ’00s it was never quite as ubiquitous as the other technologies available at that time.

The MiniDisc was introduced to solve a brief problem in technological history as well as try and replace an existing, entrenched, format. The early ’90s was a time between when audio compact discs (CDs) had been introduced into the market and started taking over but before CD burners existed for you to make your own recordings. Almost everyone recognized the superior audio quality of the CD over vinyl records and audio cassettes but the lack of being able to record audio at home was a big deal in a time when it was still popular to record your favourite song off of the radio onto cassette tape. Additionally this was a time before CD anti-skip memory (or at least before it was commonplace) and so the thought of putting CD players into cars or in portable music players, while certainly possible, wasn’t exactly ideal unless you enjoyed listening to your music skip. And don’t even think about flash based MP3 players (MP3 wasn’t invented yet) or even the iPod (which wouldn’t be introduced until nearly a decade later).

Enter the MiniDisc

Sony introduced the MiniDisc format in late 1992 as a way to solve all of the problems of CDs while benefiting from its digital nature and at the same time attempted to replace the cassette tape (although interestingly MiniDisc sort of competed against their own Digital Audio Tape as well…). So what exactly is a MiniDisc and how does it work?

Basically a MiniDisc is like a miniature CD but one that is housed inside of a protective shell.

Sort of bears a resemblance to a floppy disc.

From a technological standpoint MiniDiscs originally came in two versions: pre-recorded and recordable. Pre-recorded albums would be pressed in a similar way to that of CDs and read back using a laser. The laser would read the pits and lands on the disc in the same way that a CD laser reads a CD.

Pre-recorded discs were read the same way as CDs. You could not record on these discs.

Recordable discs were far more interesting though. These MiniDiscs were magneto-optical discs that could be recorded onto by using the laser in a high power mode to heat up a spot on the disc until it reached the Curie temperature. Once it reached this point (at around 180C) the disc could then be modified by a magnetic field. Then using a magnetic writer on the opposite side of the disc from the laser the MiniDisc recorder would modify the magnetism of that spot. In this way the MiniDisc recorder could erase (using the laser) and then write (using the magnetic writer) many times over.

There was a time when you could buy regular albums right on MiniDisc.

When the disc is later read back at a lower, normal, laser power a special property of magnetism slightly bends the laser light and causes it to reflect differently depending on the direction of the magnetic pole. This can be detected and translated back into 1s and 0s just like pits and lands.

It was a complicated process but it actually worked really well!

Now obviously being a smaller disc meant that it wouldn’t be able to store the same amount of data as a normal CD. So Sony created one of the first mainstream audio compression algorithms called Adaptive Transform Acoustic Coding (ATRAC). The ATRAC codec actually predates the MP1, MP2 and MP3 codecs by about a year… so had history turned out a bit differently we may all be listening to ATRAC files and not MP3s these days. While CD audio is encoded using linear Pulse-code modulation (PCM) at 1,411.2 kbits/second, ATRAC audio is lossy encoded at 292 kbits/second allowing the same amount of audio to be stored on a MiniDisc as a CD. Initially the quality of this audio was mixed bag, but it steadily improved over time to the point where most people couldn’t tell the difference.

MiniDisc also solved the music skipping problem by reading the data from the disc at a higher rate than it actually needed to for playback. This created a buffer that would prevent disc skipping for at least 6 seconds (as required by the MiniDisc spec). This was also important for a different reason: because MiniDiscs were random read/random write mediums this meant that if you recorded a song onto a disc that already had some space used you couldn’t be guaranteed that it would record all of the data sequentially on the disc. For example there might be some free space at the beginning of the disc, then some space taken up by an existing song, then some more free space at the end. If the new song had to be recorded in both places then the buffer would be used to allow the laser time to seek to the new section on the disc without causing the music to pause or skip.

Anyone familiar with how the old Nintendo Entertainment System loaded games would have a pretty good idea of how quite a few MiniDisc players inserted discs.

Another neat feature of MiniDiscs was that it supported Title and Artist information. If you recorded your own song you could also add that information to the track which made creating custom mixes really easy. Some recorders even let you split and re-order tracks right on the device itself.

MDLP/NetMD

Almost a decade after first releasing MiniDisc, Sony would introduce an update to the players called NetMD. NetMD’s had a few big advantages over previous MiniDisc players. Firstly they came with the latest version of the original ATRAC codec so anything recorded in that format would sound as good as possible.

Secondly it allowed you to connect your MiniDisc player to your PC via USB and transfer any music you had stored on your PC, or ripped straight from CDs, to your MiniDiscs at rates far faster than normal playback speed. While the software required to connect your MiniDisc recorder to your PC was universally loathed this still represented a big leap for the format and brought it in line with the emerging MP3 players of the day.

Finally, and perhaps most importantly, it introduced MDLP (MiniDisc Long Play) which were two new audio codecs that let you store even more music on a disc.

I don’t recall exactly but I think this is the NetMD player model I had. I have no idea where it ended up.

MDLP came in two different modes: LP2 and LP4. In LP2 mode the audio would be recorded using a bitrate of 132 kbits/second, less than half of the original ATRAC codec’s 292 kbits/second and with only a minor decrease in audio quality. This allowed you to store up to 160 minutes on a standard 80 minute disc. In LP4 mode the audio would be recorded at a mere 66 kbits/second which, while coming with a significant decrease in audio quality, meant you could store up to 320 minutes of music on the same 80 minute disc. Unfortunately these modes were not compatible with existing MiniDisc players.

Hi-MD

In 2004 Sony introduced the final, and by far largest, upgrade to the MiniDisc format in the form of Hi-MD. Hi-MD was both a new format and a new series of compatible MiniDisc players. All Hi-MD players were backwards compatible with existing discs but they also introduced a new Hi-MD disc format that was not playable in older hardware. These new discs offered 1GiB of storage capacity meaning they could hold a significantly larger amount of music than previous MiniDiscs. Hi-MD recorders also had the really neat ability to re-format older 80-miniute discs into a new Hi-MD format which would then hold 308MiB of data (about an 81% increase in storage). Even better these newly formatted discs would then benefit from all of the other new Hi-MD features as well.

1GB Hi-MD disc

Hi-MD introduced a number of new music encoding features. For the first time ever MiniDisc could now record music in linear PCM, the exact same way a normal CD is encoded, which meant that the audio quality would be identical to that of the CD source. It also introduced a new way to lossy encode music in the form of the ATRAC3plus codec suite. This mainly featured the new Hi-SP and Hi-LP recording modes which encoded the music at 256 kbits/second and 64 kbits/second respectively. Hi-LP, while using slightly less data than LP4 actually had much better audio quality as it used more modern algorithms to encode the music.

MiniDiscs had evolved from only being able to hold 80 minutes of music with the first ATRAC codec, to holding a maximum of 320 minutes using MDLP’s LP4 to finally being able to hold 610 minutes of music using the Hi-MD format and Hi-LP codec. That’s a huge amount of growth on the same disc. Using a 1GiB Hi-MD disc allowed a whopping 2,040 minutes of music in Hi-LP mode!

Hi-MD also introduced the ability to transfer perfect digital copies of recordings made on your MiniDisc recorder back to your PC, something that people had wanted to do since the introduction of NetMD. However this did come with some limitations: recordings had to have been created on a MiniDisc player (so you couldn’t transfer music files your friend put on their MiniDisc from their PC back to your PC) and even then only analog sourced recordings were allowed to be transferred (no digital/optical audio recordings).

Beyond music Hi-MD formatted discs could also be used to store arbitrary data as well making them sort of like portable hard drives when plugged into computers. Mind you the read/write speeds for data were not very good so I’m not sure if anyone actually used this beyond a few small files here and there.

Swan song

Unfortunately for MiniDisc the newer, cheaper and more fully featured hard drive and flash based MP3 players had begun to dominate the market and would eventually cause Sony to pull the plug on the MiniDisc format in late 2011. Even then MiniDisc continued to live on, for a short while, in the form of a high-end portable recording format that could be used by journalists or radio stations, before eventually being replaced there as well.

This is the Hi-MD player model I own. It still works fine to this day.

To me MiniDisc was always an interesting format. I owned both an NetMD player and later a Hi-MD player and loved them both for their crazy long battery life and small form factor. While I never really did too much with recording audio portably, I can attest that it worked great in the few times that I did actually try it. Even though I’ve since moved on from MiniDisc I’m still amazed by the amount of technology that went into such a little device.

For more on the MiniDisc, its technology and history I would recommend heading over to the excellent MiniDisc Community Portal where you can find lots of great detailed information.

Update April 10, 2016 – As James pointed out below the NetMD update alone did not allow for transfers from a MiniDisc player to a PC. This functionality was actually introduced as part of the Hi-MD upgrade.