Minidisc FAQ: Minidisc Specific Topics

  1. Do MDs skip during playback? Why not?

    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.

    Modern Sony portables (MZ-R900/700/500 and later) have an improvement to their skip resistance called "G-Protection", Sony describes it as follows:

    For the first time in MiniDisc players/recorders, Sony offers Skip-Free* G-Protection technology. Now you can jog with it, blade with it, board with it and enjoy other favorite activities while listening to uninterrupted, skip-free music. The G-Protection technology recovers laser position 10 times faster than previous designs! So it can withstand the impact of actual jogging: 8G impacts at 3 times per second.

    1. Quicker Focus Recovery...after a shock
      The laser pick-up adjusts its focal point quickly enough to react to bumps.

    2. Faster Track Recovery...returns to the right spot
      When bumped, fine access returns the laser pick-up quickly back to its original position so the data can continue to be read without interruption.

    3. High Speed Rotation...refills the memory faster
      Disc can rotate faster to read out the data much quicker.

    *Eliminates or reduces skipping during many active uses.

  2. Does the size of the music buffer vary from player to player?

    Yes. Modern MD machines (ca. 1997/98 and later) feature a 40-second read-ahead buffer (MDLP machines store 80 seconds in LP2 mode and 160 seconds in LP4 mode), but earlier machines only offered 10, and some of the first offered only 3 seconds of memory, such as the first production run of Sony MZ-1 portable MD recorders and the Aiwa AMD-100.

  3. Does MD have any special editing features for recording?

    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 [or just ``swapped'' on some early models] and named like the files in computers. For example, after recording 11 5-minute tracks on a 60-minute MD, 55 minutes are used and 5 minutes remain. If the user decides to erase track #8, the TOC gets 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 rec. button, the MD recorder seeks the next "empty" spot on the medium (according to the TOC) and starts. The resulting track consists of two separate segments of audio material: five minutes at the end of the MD and two minutes out of the space where track #8 used to be. 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... Now try that on any sequential medium (DAT, DCC, analog cassette)!

  4. What is Scale Factor Edit?

    Sony introduced Scale Factor Edit in 1999 (the first machine was the DHC-MD575 bookshelf system). Scale factor edit is a function that changes the volume level of previously recorded audio by adjusting all the scale factors in each soundgroup. Users can adjust a whole track's level, or taper the beginning and ending of tracks. This can be used conveniently, for example, to equalize the volume of tracks recorded at different levels or to soften abrupt changes in level at track boundaries. The Scale Factor Edit function modifies audio data on the disc in a completely backward compatible way, any SF editing will be revealed in subsequent playback on all MD equipment.

    The MJ Magazine MDS-JA3ES article provides a good basis for understanding how this feature works. ATRAC (and other transform audio coders) store audio in the frequency domain. The samples are stored as floating point numbers, with an exponent and a mantissa. The so-called Scale Factor is the exponent, which is stored in 6 bits, giving 64 (2^6) possible values and yielding final sample values in the range of -120dB to +6dB. Each Scale Factor step is 2dB. During an SF Edit operation, each soundgroup is read in from disc, the Scale Factors within it are incremented or decremented by a certain amount, and it is written out again. It's a much cheaper operation computationally than decoding to the full waveform, scaling it, and then recoding it.

    Scale Factor Edit does have a limitation: If you use Scale Factor Edit to decrease volume to the point that some Scale Factors in the signal become zero, the information in those samples is lost and cannot be restored by a subsequent Scale Factor Edit operation to increase volume. Likewise, if Scale Factor Edit is used to increase volume beyond the point at which some Scale Factors in the signal attain the maximum possible Scale Factor value, previously distinct Scale Factor values will begin to "max out" at the highest value and the signal's fidelity and dynamic range will decrease unrecoverably. Due to this limitation, SF edit operations that taper track endpoints to or from zero volume cannot be reversed.

  5. What is "Group Mode"?

    Introduced on the Panasonic SJ-MR220 recorder, group mode allows tracks to be placed in distinct groups ("folders") on a Minidisc. This is quite helpful when several albums are stored on a single Minidisc since each album can be placed in its own group and treated [when group mode is enabled] as if it were the only set of tracks on the Minidisc. Up to 99 groups can be created, and tracks can be moved between groups (a track cannot be placed in more than one group however). When an MD with grouped tracks is played on equipment without group mode support, the group information is ignored and all tracks are accessible. All the track grouping information is stored in a specially formatted disc title; see Brian Youn's group mode description in his MZ-R909 review for further information.

  6. What happens if I bump my player when I'm recording?

    Many users have reported problems if the MD recorder experiences shock and vibration while recording. Apparently the read-ahead buffer also works for recording, but strong disturbances could cause the laser to erase other spots on the MD, like the TOC or existing tracks, thus damaging previous recordings. To remain on the safe side, the MD recorder should not be subjected to shock or vibration while recording.

    MD drives certainly buffer during recording, otherwise MDs could not make recordings over discontiguous free blocks on the disc due to the dead time during interblock seeking. The bigger problem is, what happens when the recorder is jarred and the hot laser skids across already recorded material? One of the brochures for the professional MD units mentioned that they had a special circuit to cut the laser power when any shock occurred, thereby avoiding overwriting [much] already written material. On the normal consumer portables, you could probably lose some material when a shock occurs during recording. In any case, they're able to recover and get back on track.

  7. How flexible is the process where I put the titles of the tracks on the MD?

    The user-interface for title entry on many portable MD recorders is limited, requiring a button push to cycle past every letter. Most current home decks have a remote with a non-querty character input method. Notable exceptions are the Aiwa portable that uses the volume thumbwheel on the remote to select each character, and some modern MD decks (chiefly Sony) that allow titling with a separately available keyboard-like remote or even a standard PS/2 keyboard in some cases.

  8. Is there a limit to the length of the titles?

    The titling capacity in the Minidisc UTOC is as follows:
    1. There are 255 name blocks available, each one able to hold 7 characters, so the absolute maximum for all tracks combined is 255*7=1785 characters.
    2. The number of name blocks used by a track is: (title characters+6)/7 (rounding quotient down to nearest integer).
    3. The disc title is handled just like any other track title (the disc title is placed on track #0, which is actually the MD's free list).
    So, each track that has a title takes at least one of these blocks. This means that if you have 255 tracks, all must have titles of 7 characters or fewer, or some tracks must go without titles. It also means that MD does not have the capacity for a disc title plus 255 track titles, one track (or the disc) would have to have an empty title. In addition to these limits, certain units may not display or allow entry of long titles, for example Sony's MDX-U1 car player only displays the first 32 characters of a title.

  9. Is there anyway I can "undo" an edit operation if I delete the wrong track while editing?

    All modern (ca 1996 and later) MD decks have an "undo" function for just this purpose.

    Modern Sony MD decks also have a hidden super UNDO function. A user describes how to cancel a pending TOC update on modern Sony MD decks.

    If you have an older machine without an ``UNDO'' function, there are two approaches. If you've got an MDS-302, 303, S35, or S37, try this first:

    This machine doesn't have a specific undo function, but it can be made to forget about the edits in a simple manner, without having to open the unit. When you have deleted a track by accident for example, you just unplug the unit. Make sure that the unit isn't playing or recording before you unplug it (press the Stop button first). Now wait for about 30 secs for the power supply capacitors to discharge. Press the AMS knob, and while holding it, plug the unit back in. If you're lucky the recorder will enter in Test Mode (it always did this correctly in my case). Now you can simply press the Eject button to remove the minidisc without the new TOC being written to disc! The reason that you must enter Test Mode is because when you just plug the unit back in, it still remembers that the TOC isn't written yet. The moment you plug it back in the new TOC is written to the disc and you have lost the deleted track forever! After you have removed the disc press the Repeat button to leave Test Mode. You have to unplug the unit and plug it back in to enter the normal user mode.
    -Steven Scholte ([email protected])

    The following is a method that will work for all machines, but it requires more work:

    I'm sure everyone who has a Minidisc deck has done this. You're editing down a disc, splitting blank spots away from other tracks, then deleting the blank spots - and all of a sudden, your quick fingers just deleted the track, rather than the space. This is usually followed immediately with loud obscenities. :) I hear that some of the new units have an "undelete" feature, but my MDS-302 does not have one.

    I did this once (twice actually, within a half hour) while editing down a disc on which I had made a one-time live recording of a choral performance, that could not be re-recorded. Desparate, I remembered that the MD unit only wrote the TOC (Table of Contents) to the disc when the disc was ejected. When you do edits, it's actually only changing pointers in memory, which are then all written at once to the disc when it's ejected.

    With this in mind, I unplugged the unit while it was still turned on. I removed the case, and examined the drive mechanism. There is a large gear at the back, and I found that by turning it by hand, it worked the eject mechanism, and the disc was slowly ejected as I turned it. Once I had the disc in my hand, I plugged the unit back in.

    I figured it would be confused, so I took a blank MD, slid the write-protect tab open so that it wouldn't write to it, then plugged it into my recorder. Once it figured out that it had a new, fresh disc, I then ejected it and re-inserted the original disc with the live recording on it.

    As I had hoped, the disc had been restored, and all the edits I had made (including the one wiping out an entire track) had been forgotten.

    Now, whenever I do any editing, I periodically eject and re-insert the disc (just to write the edits to disc). This way, if I DO mess up and have to go through the manual eject sequence again, I won't lose ALL of my edits.
    -Scott MacLean ([email protected])

    The MDS-501 can me made to "forget" about editing simply by unplugging it. Even if you turn it back on and eject the same disc (without removing it the hard way) your edits will be lost.

    For the MZ-R30 portable, this will work:

    The MZ-R30 writes the TOC-Area after pressing 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 written. To Undo a delete, take away 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 and LIP-12 or LR6 AA in the supplied battery case, you must first remove all batteries before disconnecting the power adapter, otherwise the TOC-Area will be written right after disconnecting the power adaptor.

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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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