The size of an MD is 7 cm (width) x 6.75 cm (height) x 0.5 cm (depth). The disc inside is 64 mm in diameter.

It depends upon who is listening, but in any case this difference is very tiny. MD utilizes a compression algorithm (see FAQ No. 3 on ATRAC) which discards some bits from the data stream. The bits that are discarded are meant to be those that represent sound that your ears could not detect in the reproduced music. A small double-blind test made by the ABX Company indicates that people do not find a difference between ATRAC-processed music and its original. However, they can readily spot the difference when a special test signal is used for the comparison.

ATRAC (Adaptive Transform Acoustic Coding) divides the 16 bit 44.1 KHz digital signal into 52 sub-bands in the frequency domain. The sub-bands in the low frequencies are finer than the ones in the high frequency range. A psycho-acoustic transfer function that takes advantage of the masking effect and the absolute hearing threshold of man then removes enough information to reduce the data stream to 1/5th of the original size.

There are two sources which could affect the quality of the recording. One is the chain of components that brings the sound to the MD's input. If you go analogue- to-analogue, you introduce the CD's D/A Converter and the MD's A/D Converter chips, each with its own artifacts. However, if you can bring the digital data stream directly to the MD via a digital connection; then the only source of differences would be the ATRAC compression algorithm.

Coming to the second point, the ATRAC encoder then removes information from the audio signal in order to store it on the MD (5:1 compression). However, as described in FAQ No. 2, the audible difference is negligible.

Digital recording provides the most convenience when recording from CD's. No recording levels need to be set, track marks are copied from the CD perfectly, and analogue to digital conversion artifacts are completely avoided.

Rarely. A read-ahead buffer stores a few seconds of the audio material in memory during playback. The ATRAC decoder takes the data from the buffer, rather than directly from the medium. Thus, if the mechanism mistracks because of shock or vibration, the data continues to flow from memory while the MD machine recovers. If no more data remains available (when the disturbance lasts a long time), the audio material gets interrupted. Also note that the read-ahead buffer exists on every MD machine as part of the MD format.

Physically, a pre-recorded MD is just like a CD, using the same material and same production method, only the data contents are different. Unlike recordable MD's, pre-recorded MD's do not have the magneto-optical coating layers or the lubricating layers. They are made of the same plastic-aluminum structure as CD's. There is absolutely no way to record or erase anything on pre-recorded MD's.

In terms of their physical characteristics, pre-recorded MD's are manufactured exactly like CD's and are also read exactly like CD's. Blank MD's are similar but a pre-groove replaces the pits and valleys and an MO coating replaces the aluminum one. When recording, the MD machine focuses a laser on the pre-groove and heats the MO coating to the Curie point while a magnetic field aligns the metal particles (the direction depends on the data, 0 or 1). During playback, the MD machine focuses the laser on the pre-groove again, but at lower power, and registers changes in polarization (the Faraday effect).

In terms of audio quality, pre-recorded MD's are in theory no different from recordable MD's, although, as always, audio quality depends upon which version of ATRAC the discs are encoded with.

Yes. The MD format stores data like hard-disk or floppy-disk drives in computers. The TOC contains a list of starting/ending positions and names for each track, like the directory in computers. Tracks can be erased, divided, combined, moved and named like the files on a computer's hard disc. For example, after recording eleven 5-minute tracks on a 60-minute MD, 55 minutes are used up and 5 minutes remain. If the user decides to erase track 8, the TOC is updated, and now 50 minutes are used by 10 tracks and 10 minutes remain. If the user now decides to make a 7 minute recording, no problem. After pressing the record button, the MD recorder seeks the next 'empty' spot on the medium (according to the TOC) and starts.

The resulting track consists of 2 separate chunks of audio material, 5 minutes where track 8 used to be, and the last 2 minutes at the end of the MD. During playback of the 7 minute track, the read-ahead buffer keeps the audio material seamless while the mechanism jumps between the first chunk of the track and the second one.

A blank MD can handle up to approximately 1 million recordings.

Once written to the disk, data are safe from the magnetic fields and heat found in normal environments. Data stored with magneto optical technology are expected to be safely stored for more than thirty years without loss or degradation.

There is a limit of of 255 tracks as defined in the MD format. There is also an upper limit for the title and track names of 1700 characters in total.

If your machine does not have an UNDO function, there is one safe alternative: The MD unit only writes the TOC to the disc when the disc is being ejected. When you do edits, it is actually only changing pointers in memory, which are then all written at once to the disc when it's ejected. Now, whenever you do any editing, you should periodically eject and re-insert the disc (just to write the edits to disc). This way, if you make an edit mistake, you will not lose ALL of your edits.

For the MZ-R30 portable, this alternative will work:

The MZ-R30 writes to the TOC area after you clicked the Stop button or, if batteries are in use, after disconnecting the AC power adapter. After deleting anything, the R30 begins playing the succeeding piece automatically. As long as the R30 is playing, the TOC area is not altered. To Undo a delete, remove all power sources while the R30 is playing; the TOC area will be the same as before the deletion took place. But note: If you use the AC power adapter, you must first remove all batteries before disconnecting the power adapter, otherwise the TOC area will be written to immediately after disconnecting the power adaptor.