Minidisc

Sony MiniDisc MZ1 (1992), the first minidisc SONY player.

The MiniDisc, minidisc or MD, is a magneto-optical disc developed from 1992 to 2014 by the Japanese multinational Sony (and other manufacturers), smaller than the conventional CD and also less storage capacity (about 700 MB per CD compared to about 150 MB per Minidisc, although the latter was able to accommodate 1 GB per Hi-MD disc, when also the Parallel evolution of the CD led to a capacity of about 4.7 GB per DVD disc; that is, a ratio close to 5:1 has always been maintained in favor of CD/DVD in capacity and quality (due to compression ATRAC, conceptually similar to MP3). The Japanese company announced that it would stop the distribution of the device from March 2014, due to its low demand.

The Minidisc format was born primarily to replace old music cassettes and offer an editable digital recording medium.

It is a small (7 cm × 6.75 cm × 0.5 cm) magneto-optical, rewritable, magneto-optical storage disc initially designed to hold up to 80 minutes of digitized audio. The media predates the similar UMD encapsulated optical disc, known primarily for its use in the PlayStation Portable game console.

Minidisc technology was announced by Sony in 1992 and was introduced to the world market on that date. The format used for music is based on ATRAC/ATRAC3 compression, uses DRM, different bitrates, and direct sampling from a digital or analog signal. In Japan they became a substitute for cassette tapes, but not in the rest of the world. They became popular in the UK for three years (1999-2001), when music albums (also known as 'pre-recorded' minidiscs) were released.

The main advantage it offers is its reliability as a portable sound storage device.

MiniDiscs are smaller than CDs, with a diameter of 64 mm, but their data transfer speed is lower: 292 Kbit/s, compared to the 1.4 Mbit/s required by CD (here there is also an approximate ratio of 5:1 in favor of CD). It delivers a 16-bit resolution, using the standard 44.1 kHz sampling rate.

History

Several rewrapped minidisc with different durations (60 ~ 80 minutes), which have been updated over time.

The MiniDisc, along with the DCC from Matsushita and Philips, was designed to replace old cassette tapes as a recording system, but it was not as successful as expected. It did not gain a foothold in the US or European market, it only became really popular in Japan, where it came to capture more than 50% of the market for portable music players, although since about 2002 it has been gradually replaced by players based on in flash memory, or those based on a hard drive (such as iPod), mainly with the mp3 format as the main attraction.

Its discreet initial success was attributed to the small number of albums available for sale, because very few publishers and record companies accepted this new recording format (discs released on MD disappeared from the market at the end of 2001). The high cost of playback/recording equipment and the growing popularity of the mp3 format also had a lot to do with it.

Instead, the minidisc was widely used by musicians and live recording enthusiasts, due to the high quality of the format. It was also widely used by studios and radio stations, until around 2010, when they were progressively replaced by hard drives as a means of recording news and storing broadcasts.

Primarily responsible, Sony, perhaps made the mistake of the 1970s with the Betamax video system again, and took a long time to license MD technology to other manufacturers such as JVC, Sharp, Pioneer, Yamaha and Panasonic, to each produce their own minidisc systems.

Magneto-optical recording

The minidisc uses a digital sound recording system. Magneto-optical recording is a combined system that records magnetically, but reproduces optically.

Data is written to disk using what is known as phase change coating.

The surface of the disc, while under the influence of a magnetic field, is heated by the laser used during disc reading (with higher power in the case of recording). In this way, the heat generated causes the surface of the disk to reach a critical temperature known as the Curie point (about 180 °C). When the metal alloy that makes up the disc reaches this temperature, it modifies its own structure (state of crystallization). Taking advantage of this change in the state of crystallization, the magnetic flux aligns the crystals in opposite directions.

By cooling the disk rapidly, the induced magnetism remains. This is because by rapidly cooling, less light is reflected, and the material no longer recrystallizes properly, so it does not return to its original state.

Thus, the binary information is stored permanently. Manufacturers claim that it is possible to store data for 30 years without distortion or loss.

Like a compact disc, the minidisc stores music in tracks.

Digital playback and anti-skip

To reproduce the data, the laser simply lowers the power and reads it optically, just like a conventional CD drive.

During sound playback, the minidisc uses a buffer that allows it to read the stored data ahead of time. A buffer is a temporary storage memory for digital information, which allows it to be read while it is waiting to be processed. This buffer makes it possible to eliminate the "jumps" that occur when the equipment is subjected to strong vibrations. the player already has stored in memory what it should play, plays it back and gives the reader time to recover. The latest equipment incorporated a buffer of at least 40 seconds, which makes it very difficult for an interruption in the sound to occur, a circumstance highly appreciated among athletes who are fond of listening to music.

Differences from CDs and cassettes

Sharp MD-MS701H

MDs store data on a magneto-optical material. Unlike the old cassette tapes, the disk is a random access medium, the access time of which is much less than that of the previous ones. This allows them to be quickly edited on portable drives. Sound tracks can be easily cut, merged, reordered, or deleted (they are not instantly deleted, just marked as such). It can be recorded and erased thousands of times, according to the manufacturers. At the beginning of the disc, there is a table of contents (TOC), which stores the starting position of the tracks it contains, as well as other information such as their title and artist. The editing of the name of the artist or song should be done by hand (for portable players) or with the help of an external keyboard (for professional recorders). The number of characters that can be used for the text is limited to 1785 letters to be distributed among all the tracks.

Unlike tapes, a track can be fragmented throughout the disc, in fact, the first MiniDiscs allowed a minimum fragment of 4 seconds of audio. Chunks smaller than that size were still stored in a block, reducing the actual capacity of the device. The recorders take advantage of the blocks marked as erased to store the new audio tracks, but no means is provided to defragment the disks at the user level, since the operation would require two MDs (or enough RAM to store the entire contents of the disk)., as well as a processor capable of putting the fragments in order so that each track occupies only one on the disk. Disk fragmentation is the main reason the player has buffer memory, because while the player searches for the other chunk of the song, it has to play something in order not to cause playback to stop. The only problem that causes fragmentation is excessive seeking, thus reducing battery life.

Another advantage that MD has over other types of audio players (MP3, HDD, etc.), is that the audio is stored in consecutive bit “strips”, and the TOC is the one that stores the pointers to the bits. tracks, allowing them to be played without pausing between them.

At the end of a recording, when the “STOP” button is pressed, the device will continue recording the data it has in the buffers for a few seconds. Once this is done, it will move on to recording the TOC. It is recommended not to remove power from the appliance or shake it during this operation. It is recommended to keep the power connected to the device during the entire recording, as it significantly reduces battery life.

All devices are provided with an anti-copy protection known as Serial Copy Management System, which allows you to copy an unprotected disc or song as many times as you want, but the copies cannot be copied again, except if they are transferred to analog format.

There are also differences related to the musical experience that are based on the equalization of the channels that occupy the bass and treble frequencies more accurately than in most devices offered to the public. MD also incorporates some features that allow you to vary the playback speed to optimize the tempo or beat of your recordings.

ATRAC compression

Sony MZ-RH1 minidisc player, Hi-MD compatible

The minidisc, as a channel code (audio codec), uses the compression system ATRAC (Adaptive Transform Acoustic Coding). It is an encoding algorithm that offers a compression ratio of 1:4.83. That is, it manages to reduce the data load to 1/5 of what the original signal would need or what a CD would require.

ATRAC uses perceptual coding which is a lossy coding system. Perceptual encoding is based on human hearing capabilities. When we receive a large amount of sound stimuli, our ears only allow us to hear those with the highest intensity, the rest are masked and cannot be heard. For the same reason, the ATRAC eliminates the frequencies that the human ear cannot recognize, leaving only the audio frequencies (20 to 20,000 Hz).

Each of these three signals is analyzed and filtered independently, using the modified direct cosine transform MDTC, which gives rise to subgroups of between 20 and 16 subbands for each of the 3 frequency bands.

In the beginning, due to the high compression rate of the ATRAC, it was not used to work with audio at a professional level. ATRAC encoders have improved considerably over time since the first generation, and ATRAC versions are now (2005) available that produce audio signals that sound virtually identical to the original source.

MD Applications

MD 80 Memorex

As the data compression on the minidisc is considerable, it is not used as a master for professional audio, although it is used by journalists, since they offer better features than conventional recorders. It allows high-fidelity home recordings to be made, providing the user with advanced editing options.

In essence, the MiniDisc works like a floppy disk, so that when you erase or move tracks, the space available for recording remains constant, something impossible to achieve with sequential access media like old cassettes. A MiniDisc can be rewritten up to a million times without deterioration.

The minidisc market segment is currently (2016) in selective domestic consumption and in specific applications in radio stations.

MDLP

In 2000, Sony released a new generation of minidiscs equipped with a technology called MDLP (Minidisc Long Play). This allows up to 300 minutes of music to be stored on a common 74-minute disc, thanks to a new compression method known as ATRAC3, which has three recording modes:

1. SP, maximum quality, 292 kbit/s, standard with 74 minutes of recording, stereo.
2. LP2, high quality, in which 150 minutes can be stored, 132 kbit/s, stereo.
3. LP4, medium quality, where 300 minutes are reached, 66 kbit/s, stereo.

NetMD

In 2002 NetMD appeared, a format that allows downloading music from the computer to the minidisc at speeds of up to 64X, connected by means of a USB cable. All NetMD players also support the MDLP format. It can only be used with proprietary software under Windows (SonicStage), although there is also a free (Unix-like) version called libnetmd.

Hi-MD

Hi-MD minidisc manufactured by Sony

This new format was introduced in 2004. Hi-MD players and recorders use a new codec called ATRAC3plus, and have the ability to store any type of file on their discs, be it data or music. They work with three types of discs:

1. Conventional discs (standard MD): Hi-MD devices have the same functionalities as NetMD and MDLP when working with these disks, do not differ from the original MD devices.
2. Conventional discs (standard MD) formed to Hi-MD by an Hi-MD player: they have a 305 MB gross data capacity (RAW), unlike the 160 MB that conventional ones allowed.
3. Hi-MD discs: they only work in Hi-MD players and allow to store up to 1 GB of raw data. Although they have the same form and dimensions as conventional ones, they cannot be used on original MD devices.

The last two types of discs have the following characteristics:

• The new ATRAC3plus codec, whose bitrates can be 352, 256, 64 or 48 kbit/s, plus a PCM linear recording mode.
• Connected to a PC, they can store any file type, similar to a USB memory.
• NetMD cannot read Hi-MD disks (not even formatted).

In 2005, Sony announced a new model with the ability to take digital photos with a built-in camera, plus all the benefits of Hi-MD.

A 1 GB Hi-MD disc can store 1 hour and 34 minutes of music in PCM audio format, 8 hours in ATRAC3plus (256 kbit/s) and 34 hours (64 kbit/s) ATRAC3plus.

Recording modes

The modes marked in green can be performed from the MD player, and those indicated in red from a PC:

Data storage: MD Data

Although MDs were initially designed to store audio, Sony announced in 1993 a new version called MD Data for data storage, which never caught on. It was capable of storing up to 140MB, but access times were too long and write speeds slow compared to other media. The MD Data could not be used like a conventional MD, and it was much more expensive. Later Sony released the 650 MB capacity MD-Data2, which was used only by camcorders designed for MD.

In 2004, the aforementioned Hi-MD appeared, which allows you to store up to 1GB of data or audio.

Software

Sonic Stage

This is Sony's proprietary software used to control MD portable devices, when connected to a PC running Windows operating system. It is very similar to other programs such as Windows Media Player or Real Player, it uses the ATRAC OMG/OMA library to record on the PC, and it had a function to download songs from the Internet ("Connect" module, canceled in March 2008).

This program was designed to respect the copyright of the music that Sony sold, so the players in general did not allow you to "drag" songs directly to the PC, and the same thing happened from one player to another. Currently (2016) it is not so strict, especially since the introduction of version 4.3, since the program supports the MP3 format.

It also allows you to create a hierarchically structured database with the songs that the user has.

The main attraction of this program is the possibility of digitally downloading the audio stored in the minidiscs to the PC:

• If you want to flip the content of a NetMD or Hi-MD disk, it serves any player of such disks.
• If you want to download the music from a conventional CD (standard) or an album (pre-recorded), then you must use the Sony MZ-RH1 model.

Version 4.3 is the latest (as of 2016) for western languages, which officially supports Windows Vista (and earlier), but usually works fine on Windows 7 (32 bit). To operate SonicStage in Windows 7 (64 bit) or Vista (64 bit) a driver called "NetMD USB driver" must be downloaded, so that the minidisc connected to the USB port of the computer can be effectively recognized by the system. operational, and make data transfers.

Version 4.4 is available in Japanese only.

Libnetmd

It is an implementation of a freeware set of tools to be able to use NetMD recorders under operating systems that support POSIX (Linux, Net/Free/OpenBSD and MacOS X). The project also includes an application called "netmd" that uses this library. Currently allows:

• Rename and move tracks/groups/disco.
• Print the TOC of the disc.
• Create/board tracks/groups.
• Play, pause, advance, rewind and stop.