Frequently Asked Questions |
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| ATRAC 1 | ATRAC 2 | ATRAC 3 | ATRAC 3.5 | |
|---|---|---|---|---|
| Introduction | 1993 (Too early due to DCC) | 1994 | 1995 | Current |
| Threshold | 15KHz | 18KHz | 18KHz | 18KHz |
| Noise | Big! | Much lower than ATRAC 1 | Dynamic filter: no noise in breaks | ==DAT |
| Sound | metallic | close to DAT | no difference to DAT in "blind listening test" | ~=DAT |
| Sparkling Noise | hearable | not much better | only hearable in very silent passages | gone |
| ATRAC 1 recorder MDS-101 | ATRAC 2 recorder MDS-501 | ATRAC 3 recorder MDS-303 | ATRAC 3.5 recorder MDS-JA3ES | |
|---|---|---|---|---|
| ATRAC 1 Player | (see table above) | 15KHz! Less noise | 15KHz! Less noise | 15KHz! Less noise, "sparkling noise" gone |
| ATRAC 2 Player | 15KHz threshold! Less noise, still metallic sound | (see table above) | No difference from ATRAC 2 recorder | No "sparkling noise", a bit less noise (as when recorded with 2.0) |
| ATRAC 3 Player | No big difference from above | No difference from ATRAC 2 player | (see table above) | No "sparkling noise", a bit less noise (as when recorded with 3.0) |
| ATRAC 3.5 Player | No big difference from above | "sparkling noise" still not better, but less noise than above | low level "sparkling noise" remains, a bit less noise than above | (see table above) |
In general, all ATRAC versions are fully compatible with each other. However, if you play or record something with 1.0 the result will be rather poor no matter from which version the source came from or goes to. If you take a higher version the result is generally be good enough, when you use ATRAC 3.5 for either playing or recording it gets even a bit better. For portables and car-players with 3.0, the weakest link is the A/D converter.The practical result: buy a 3.5 or better for 'home use', record there, and you get better quality in your 3.0 portable or car-player.
| ATRAC 1 to ATRAC 1 | After 5 generations unacceptable, after 20 generations awful. |
| ATRAC 2 to ATRAC 2 | After 5 generations no hearable difference, after 20 generations tiny distortion. |
| ATRAC 3 to ATRAC 3 | Not much better than with ATRAC 2. |
| ATRAC 3.5 to ATRAC 3.5 | Slightly better than ATRAC 3, relating to noise. |
There is not much information about this other than what Sony says in their brochures and what appears in occasional magazine articles (thanks primarily to Japanese MJ and German Stereo magazines for their detailed reporting). Since ATRAC's transform window size (11.6ms) and signal processing structure are fixed, the improvements come primarily through improvements to the signal processing step's mathematical accuracy and refinements to the bit allocation process. In brief:
| ATRAC 1 | 16x16 bit multiplication |
| ATRAC 2 and 3 | 16x24 bit multiplication |
| ATRAC 3.5 | Block Floating type calculation to improve performance on smallsignals (see: Japanese MJ Magazine MDS-JA3ES review) |
| ATRAC 4 | 24x24 bit multiplication, frequency response still 19kHz (see: on ATRAC 4) |
| ATRAC 4.5 | Adaptive High Band Control, frequency response pushed to 20kHz,noise lowered 3dB through higher computation accuracy (see: MDS-JA50ES review) |
| ATRAC using Type-R DSP | Faster DSP allows two pass bit allocation algorithm that looks forredundancy and makes better use of available bits, providing further improvements to high frequency performance. (see: using Type-R DSP) |
A short paper by DJ Greaves goes into further detail about S/PDIF, and has some comments about why jitter is not a problem even in equipment without buffers. Another paper by Tomi Engdahl goes into great detail about S/PDIF, even giving schematics for AES/EBU <-> S/PDIF conversion. Finally, Digtial Domain has written a very comprehensive paper on jitter in digital audio systems.
Sony, in the process of developing ATRAC, unknowingly employed techniques that were covered in prior Dolby patents. Sony made a licensing agreement with Dolby to avoid (or as the result of) a legal challenge from them. Dolby doesn't own all of ATRAC, just some part(s) of it.Nu het antwoord:
"I have done extensive testing with this, and have yet to find a single instance where the MD encoding/decoding affected the Pro-Logic encoding in any way. In every test I did, the surround steering information remained intact, and the result sounded precisely like the original." ~ Scott MacLean (scottm@netbound.com)
Kortom: onder normale omstandigheden wordt Dolby ProLogic Surround geluid perfect opgeslagen en weergegeven.
Physically, a pre-recorded MD is just like CD, using the same optical parameters, material, and production methods. Only the data contents are different (compressed ATRAC audio vs. 16 bit linear PCM audio). Unlike recordable MD, pre-recorded MDs do not have the magneto-optical coating layers or the lubricating layers. They are made with the same plastic-aluminum structure as CDs, so there is no way to record or erase anything on them. Prerecorded MD's are also read exactly like CD's (the player focuses a laser on pits and valleys within a transparent polycarbonate substrate backed by a coating of aluminum thus reflecting or dispersing the beam).Recordable MD's are similar, but a pre-groove replaces the pits and valleys and an MO coating replaces the aluminum one. When recording, a laser is focused from one side of the disc onto the pre-groove and heats a spot on the MO recording layer to its Curie point while a magnetic field from a head in contact with the other side of the disc aligns magnetic dipoles within (read magnetizes) the heated spot on the MO layer (the N/S orientation corresponding to 0s and 1s in the data). During playback the MD machine focuses the laser on the pre-groove again, but at lower power, and the data is read back by measuring changes in polarization of light reflected from the previously magnetized regions (the Faraday effect).
In order to playback both pre-recorded and recordable media, all MD units have a dual function optical assembly which can, depending upon the disc type, detect changes in either reflectivity or polarization.
In terms of audio quality, pre-recorded MDs are in theory no different than recordable MDs, although, as always, audio quality depends upon which version of ATRAC the discs are encoded with. Some users have noticed certain pre-recorded MDs that sound worse than a homemade copy of the same CD with a modern MD recorder. It's likely that the ATRAC encoders used for prerecorded MDs are improved over time just as they are in the consumer units.
Finally, recordable MDs have an extra hole in their case, which is sensed by a microswitch within the MD unit that connects to the REFLECT pin of the microprocessor. It tells the MD player's microprocessor whether signal reflectivity is high (for pre-recorded) or low (for recordable).
Lay-out:On recordable MDs, 32 out of 36 sectors in every cluster (the smallest recordable unit) are used for storing audio data. Of the remaining 4 sectors, 3 are needed to accomodate the start up and run out of the error correction code, as stated in the MiniDisc IEEE paper: ``Because of the long interleaved ACIRC error correction code, three sectors must be used as "linking sectors." If the user changes or adds new data to the MD disc, two or three sectors for every start and end position of the new data need to be recorded.''. In other words, some space is wasted to accomodate re-recordability. On pre-recorded MDs, however, the data is fixed during mastering as one continuous stream, so these 3 extra sectors can be devoted to sub-data (but there is no documenation as to what this extra sub-data space could be used for). The Sony DADC MD handbook says that the maximum duration of a pre-recorded MD is 78:16.
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.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.
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 (scottm@netbound.com)
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.The MDS-503 (and up) has an "undo" function for just this purpose.
No, there is a read-only label track on each MD that distinguishes an MD Audio and MD Data disc, MD equipment looks at this label to determine what kind of disc it is accessing. An MD audio disc inserted in an MD Data drive shows up as having 1k in disc, 0k available. The ATRAC encoded music information is not accessible. An MD Data drive user has written some information about the MD Data drive and cross compatability.
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