I guess it's a matter of marketing-a witches' brew of guesswork and self deception
when last I studied it. Philips initially launched DCC in the home market and
touted its CD-quality sound. Sony launched MD in the portable market and
pushed convenience over sound, which was simply described as "approaching" CD
quality. Well, the Philips camp now has portable DCC players and, with the
MDS-501 deck, Sony catapults MD into the "high-fidelity home market." Having
lived with the MDS-501 for a while now, I must say that I'm impressed with
how simple and intuitive it is to operate and by the seemingly amazing things
it can do. When you get right down to it, some of these features are not
really that amazing to computer buffs, who have been "erasing" entire
files (read, "programs") with a single command for years. It is
novel, however, to have this facility right at your fingertips in a music
recorder. Until recently, not even professionals could instantly wipe a bad
take, move tracks around, or combine tracks at the press of a button! As
a storage medium, MiniDisc re ally does bridge the gap between the computer
and audio worlds.
Control Layout and Editing Functions
As the first Sony home product of a new format, the MDS-501 follows what appears to be Sony's standard philosophy, i.e., load the first product with features and functions and see which ones consumers actually use. For example, the MDS-501 has a built-in clock that automatically time- and date-stamps each recording as it is made.
(However, setting the MDS-501 for unattended recording or playback requires an accessory timer.) For private listening, there's a headphone jack at the lower left of the panel and, next to it, a level control dedicated solely to headphone operation.
Headphone output power is generous, the impedance should match most headsets reasonably well, and the independent level control makes the headphone jack useful rather than a mere afterthought.
The MDS-501 has both analog and digital inputs and outputs, the former via conventional gold-plated pin ("RCA") jacks, the latter exclusively via optical Toslink connectors. And needless to say, the MDS 501 includes SCMS to prevent more than one generation of digital-to-digital dubbing. (One might question the degree to which SCMS is needed on an MD deck, since multiple passes through the perceptual encoder/decoder will eventually "un mask" hidden noise components.) The MDS-501 accommodates only digital sources that use a 44.1-kHz sampling rate, i.e., CDs and prerecorded DATs. Digital broadcasts (which operate at 32 kHz) and DATs recorded at 32 or 48 kHz (the default rate) cannot be digitally dubbed onto the MDS-501; you must therefore use the analog inputs.
Control operation is intuitive. The disc slips into a slot, its presence indicated by an orange lamp. An "Eject" button lies be right of the slot. To its right, under the display, are play, pause, stop, and record buttons. Pressing "Rec" puts the ...
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SPECS
Frequency Response: 5 Hz to 20 kHz, ±0.5 dB.
Playback S/N: Greater than 98 dB.
Wow & Flutter: Below measurable limits.
Line Input Level: Nominal, 500 mV rms; minimum, 158 mV rms.
Line Input Impedance: More than 47 kilohms.
Rated Output: Line, 2 V rms into 50-kilohm load; headphone, 28 mW into 32-ohm load.
Dimensions: 17 in. W x 3 3/8 in. H x 14 in. D (43 cm x 8.5 cm x 35.5 cm).
Weight: 11 lbs., 7 oz. (5.2 kg).
Price: $999.95.
Company Address: Sony Dr., Park Ridge, N.J. 07656.
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AS A STORAGE MEDIUM, MINIDISC REALLY DOES BRIDGE THE GAP BETWEEN THE COMPUTER AND AUDIO WORLDS.
.... deck into record/pause mode; pressing the play or pause control then starts the recording. The track number goes up, with the new track number stored in a temporary table of contents (TOC), each time "Rec" is pressed. If you forget to hit "Rec" when you want to change track numbers, don't worry; the MDS-501 has extensive editing facilities, which I'll get to presently.
Analog recording level is set with a tightly clutched, dual-concentric control that lies at the upper far right, behind a hinged door. Recording level is displayed by a better-than-average LED meter whose range is-40 to 0 dB. An "Over" indicator warns when you've pushed matters too far. When dubbing a digital source, the original level is duplicated automatically, with no need for manual level adjustment.
The "Display" button, adjacent to the re mote sensor, toggles the display between the title of the current track and the remaining playing time of the disc. Above these buttons is a multifunction "AMS" dial that's used to cue to the beginning of specific tracks, set the clock, specify the playing order of programmed tracks, enter text data, and control the editing functions.
The MDS-501's editing facilities are both extensive, as I said above, and unfamiliar. All editing is accomplished with controls behind the front-panel door. The most important of these are two editing buttons, "Edit/No" and "Yes," which-of ten in conjunction with the other editing controls-are involved in virtually all edit operations.
Pressing the "Edit/No" pad cycles through all currently available options; when you get to the one you want, you press "Yes." Some of the options are "toggles," i.e., if you have Level Sync on and you want to turn it off, you press "Edit/No" until "Level Sync ON" appears in the display and then press "Yes" to toggle it off. Whether Level Sync is on or off, pressing the "Rec" but ton will raise the track number.
If you press "Edit/No" while in the record/pause mode, "Level Sync ?" will appear in the display.
If you then press "Yes" twice, the display indicates "Level Sync ON," and a new track number is record ed each time the input level drops below a specific level (-80 dB when digitally dubbing a CD) for 2 seconds or more. (During recording, pressing "Edit/No" displays "Name in ?"; a second tap is needed to advance to the "Level Sync ?" option.) You can erase, divide, combine, and move tracks after they've been recorded. To erase a track, advance to it with the "AMS" knob, press "Edit/No" consecutively until "Erase?" appears in the display, and then press "Yes." When the track has been deleted and the TOC updated, the display indicates "Complete." You can erase an entire disc by tapping "Edit/No" until "All Erase ?" appears and then pressing "Yes" twice. You can even erase portions of a track by dividing the track into segments (each of which will be individually numbered), erasing the segment you want to remove, and combining the remainder. (Just like a 31/2-inch floppy, an MD can be protected from erasure by sliding a tab on its shell.) To divide a track, pause the disc at the appropriate point, press "Edit/No" until "Divide ?" appears in the display, and then press "Yes." "Rehearsal" flashes in the display, and the starting point of the new track plays back repeatedly with a "Position ok?" legend. If it's okay, press "Yes"; the display will show "Complete." If the dividing point is inappropriate, press "Edit/No" and adjust the "AMS" dial to get to the de sired point. In this mode, "AMS" has 256 steps, covering the range from -7.68 to +7.62 seconds in 60-mS increments.
Fig. 1-Record/play frequency response.
Fig. 2-Record/play THD + N vs. frequency.
Fig. 3-Record/play THD + N vs. record level.
Combining tracks is similar to dividing them. Turn the "AMS" knob until the track you wish to append is shown in the display, press "Edit/No" until "Combine ?" appears, press "Yes" to enter the "Rehearsal" mode, and-if all is as desired-press "Yes" in response to "Track ok?" Although only consecutive tracks can be combined, you can move tracks so that the ones you wish to combine become consecutive. Select the track you wish to move with the "AMS" knob, press "Edit/No" until "Move ?" is displayed, press "Yes," adjust the "AMS" knob to specify the new track position, and press "Yes" (or the "AMS" knob).
Once you get the hang of the "Edit/No" and "Yes" buttons, the display guides you through each procedure; the system is easy to use and remarkably flexible. The flexibility comes from MD's random-access recording, essentially similar to that of a computer hard or floppy disk. When you "erase," "move," or "combine" tracks, no data is actually erased, moved, or combined. Instead, the table of contents is ...
Fig. 4-Deviation from record/play linearity.
Fig. 5-Record/play channel separation.
Fig. 6-Fade-to-noise test (dither applied)
Fig. 7-Spectrum analysis of test-tone and "no-signal" tracks.
... changed to indicate where the data lies on the disc and which portions of the disc are available for overwriting because they have been "erased." Bear in mind, however, that all edits exist only in a temporary TOC until you stop the deck and eject the disc.
That action records the TOC on the disc. If you switch off power before doing so, the edits are lost. You're limited to 255 track marks on any one disc, but it should be enough to keep you busy! The remaining controls behind the front-panel door are "Play Mode" (which selects among normal, "Shuffle," and "Pro gram" play), forward and reverse search, "Repeat" play, "Timer" (for unattended recording or playback), and "In put" (to choose between the analog inputs and the digital inputs for recording).
The remote control provides direct access to any track via 25 numeric keys and a ">25" button that permits access to higher numbered tracks. (Press ">25" followed by number-by-number en try of the track you wish.) "Date/Recorded" and "Date/Present" buttons display the recording date of the selection or the current time and date. "Repeat" replicates the function of the corresponding panel button. With the remote's "A-B" button, you can also mark the start and end points of a segment you wish to repeat. A button for auto spacing inserts 3-second blank spaces between tracks during play (helpful when making a tape dub of an MD for use in a tape player that searches for blank spaces) and, when pressed twice, automatically pauses after each track. A music scan feature plays the beginning of each track, in succession.
All operating-mode controls (play, pause, stop, record, and search) are available on the re mote; a pair of buttons with the standard skip marking duplicates the action of the front panel's "AMS" knob. The remote also has "CD-Sync." and "CD Player" but tons, which work with Sony CD players. The three "CD-Sync." but tons ("Standby," "Start," and "Stop") facilitate dubbing from the player. The "CD Player" pause and skip buttons temporarily stop and start playback and find desired tracks.
The MiniDisc format supports alphanumeric titling of the disc and each program.
With prerecorded MDs, the album title pops up when the disc is loaded, and titles change with each track. A "Scroll" button on the remote moves the display through titles longer than the display's 12-character maximum and then redisplays the initial 12 characters.
You can label your own recordings, but the procedure is not very convenient. You enter the data during playback, letter by letter, using either the "AMS" dial on the front panel or buttons on the remote. As long as you don't care to use certain special characters available only via "AMS," the latter approach is definitely preferable. On the remote, the three "Play Mode" buttons, the two "Date" buttons, the "Repeat" and "A-B" buttons, the 25 numeric keys, and the ">25" pad individually access each letter of the alphabet and a few common punctuation marks.
THE EXTENSIVE EDITING FACILITIES LET YOU DIVIDE, COMBINE, AND EVEN MOVE TRACKS AFTER RECORDING.
If you do use the "AMS" dial to label a track, access the "Name in ?" function with "Edit/No," press "Yes," and start punching in letters. By using the search buttons, you can move a flashing cursor under any in correct character and then either enter the correct one or press "Edit/No" to erase it.
When you've finished (which you must do before the end of the track), press "Yes." Again, you must stop and eject the MD to record any titling on the disc. (Whenever you've made a temporary change in the table of contents, a "TOC" indication appears in the display to remind you not to turn off power until you've stopped and ejected the disc.) You have two setup options before recording. These determine whether new recordings will be appended to those al ready on the disc or whether the disc will be erased entirely and recorded from the beginning. Here's the only place where I found Sony's nomenclature slightly con fusing. The "append" mode is designated "All REC OFF" and is the factory-default setting. The "erasing" mode is designated "All REC ON" and must be selected before inserting the MiniDisc using (you guessed it) the "Edit/No" and "Yes" buttons.
For dubbing from a digital source, the MDS-501 has a non-defeatable "Auto Cut" feature that stops recording if the level drops below-80 dB for 20 seconds. When this occurs, the display flashes "Auto Cut," and the last 18 seconds of "silence" are automatically "erased." This is probably a good feature in the real world, since you can copy a CD unattended and not waste space recording silence even if the CD runs out before the MiniDisc does. However, if you want to record "silence" (as I did for certain lab tests), the MDS-501 thwarts your attempts. You can get around this by pausing the recording before the 20 seconds are up, restarting it, and "combining" the tracks afterward. I got lots of practice at that!
Measurements
The only test MiniDisc that I know of is Sony's MD Audio Test I for Signal Performance (TGYS 1). This disc was made by converting the master tape of Sony's Test CD Type 3 (YEDS-7) to MiniDisc, with the input levels reduced by 0.05 dB. While a good disc in its day, the YEDS-7 has been pretty much supplanted by the CBS CD-1, which is the EIA-recommended test CD and has a number of useful tests that are available on no other disc. I ran the MDS 501 through its paces using the TGYS 1 and then made a digital copy of the CBS CD-1 onto MD. I used this disc for my dig ital record/play data. Finally, I made recordings from the analog inputs to an other MD for my analog record/play data.
Frankly, I flipped out when I found that, within the limits of experimental error, the digital dub of the CD-1 matched the performance data of the professionally encoded TGYS 1 in frequency response, distortion, and A-weighted signal-to-noise ratio! Even in quantization noise and dynamic range, the digitally dubbed disc was no more than 1 dB worse than the profession ally encoded TGYS 1.
To be specific: The A-weighted S/N was 98.3 dB at 0-dB recording level for either playback of the TGYS 1 or record/play from the CD-1, the record/play dynamic range was 93.9 dB from the CD-1 versus 94.9 dB from the TGYS 1, and the figures for quantization noise were even closer (88.3 dB for record/play versus 89.1 dB for playback of the Sony test MD). Response and distortion data taken from the TGYS 1 were identical with those from the CD-1 dub, so I have not presented them.
You may ask, "What's so surprising about a perfect dub? Aren't digital dubs supposed to be perfect?" Well, perhaps so when recording from one 16-bit linear sys tem to another, e.g., from CD to DAT. But that's not the case with MD. When digital data enters the MDS-501, it is ATRAC-en coded using Sony's perceptual algorithm before recording. It's not at all apparent that the encoder in a consumer MiniDisc recorder would match the professional sys tem used to make the TGYS 1. I find it quite impressive that the MDS-501 en coder is as close to professional standards as it is! Equally impressive, if not more so, is the recording performance from the analog in puts. Frequency response (Fig. 1) is within ±0.05 dB from 21 Hz to 19.4 kHz for recording via the analog inputs compared with ±0.03 dB from 20 Hz to 20 kHz on the digital dub. I'm not sure what caused the rise to +0.18 dB at 20 Hz in the recording made from the analog inputs, but the droop to-0.64 dB at 20 kHz is undoubtedly due to the anti-aliasing filter.
Record/play THD + N at 0 dB versus frequency (Fig. 2) is negligibly worse from the analog inputs than from the digital.
ON MOST MATERIAL, YOU'LL DISCERN NO DIFFERENCE BETWEEN CD AND SECOND-GENERATION MD.
(Here and in other plots where the curves for the left and right channels were close to identical, I have omitted the right-channel curve for clarity.) It's interesting to note that the peaks in the analog distortion curve occur at frequencies where there was no digital data on the CD-1 I dubbed from. (The digital data points on the CD-1 disc occur at rather widely spaced intervals, and my test gear smooths the response curve between them; I make the analog sweep in much finer increments.) And THD + N versus level (Fig. 3) again is only a few dB worse on recordings made from the analog inputs than on those from the digital.
Linearity error (Fig. 4) is virtually identical (and negligible) whether the analog or digital inputs are used. (In the case of the analog inputs, the results include linearity error of the A/D converter.) Only in channel separation (Fig. 5) is the digital option measurably superior. And since we're speaking of separation in excess of 70 dB, even when using the analog inputs, it's hard to believe that the difference will be audible.
Only the CBS CD-1 disc provides a fade-to-noise track. The results (Fig. 6) testify to excellent low-level linearity in the MDS-501's D/A converter. The spectrum analyses (Fig. 7), which I measured using the Sony TGYS 1 disc (results were the same for the CD-1 copy), exhibit remark ably low hum contamination and good noise shaping.
Just to round out my tests: Record/play channel balance was perfect when recording from the digital inputs and was within ±0.045 dB with the analog inputs. Analog input sensitivity for 0-dB recording level was 0.594 V rms, and output at 0 dB was 2.1 V rms.
Use and Listening Tests
Failure to deliver adequate performance on the type of bench tests described above will preclude the possibility of good sound.
But getting high marks on these tests (which the MDS-501 certainly did!) does not guarantee good sound, especially when we're dealing with a system that uses perceptual encoding to economize on data rate. Ultimately, sound quality is established in the listening room.
So, the $64,000 question: Does the MDS-501 deliver CD-quality sound? Let me answer it this way: If you did not have a CD version of the same program to com pare with, and you did not know you were listening to a MiniDisc, I'm quite confident that you'd believe you were listening to a CD. The sound of this second-generation Sony MiniDisc recorder is that close to what we now consider the standard, i.e., the CD. Furthermore, I've heard many CDs that sound far worse than the commercial MD software I auditioned on the MDS-501. On most material, even if you did have a CD version of the same pro gram for comparison, I doubt very much whether you'd discern a difference.
But is the sound identical on all material under all circumstances? Not quite. I've accumulated a number of discs that are particularly hard on perceptual encoders.
Some of the signals were used by the Motion Picture Experts Group (MPEG) in evaluating audio compression systems, to separate the men from the boys. When I digitally transferred certain tracks to MD and made A/B comparisons, I could hear a difference. Although the test was not double-blind and thus is suspect, I convinced myself I could reliably tell the original from the copy-just barely, but different nonetheless.
The differences occurred in three areas: A slight suppression of low-level high-frequency content when the algorithm needed most of the available bitstream to handle strong bass and midrange content, a slight dulling of the attack of percussion instruments (piano, harpsichord, glockenspiel, etc.) probably caused by imperfect masking of "pre-echo," and a slight "post-echo" (noise puff) at the cessation of a sharp sound (such as claves struck in an acoustically dead environment). The second and third of these anomalies were most readily discernible on single instruments played one note at a time in a quiet environment, and were taken from a recording specifically made to evaluate perceptual encoders.
With regular music recordings, pre- and post-echoes seem to be reasonably well masked by the natural reverberance of the recording, although a slight thickening could be noted when listening to digital dubs of harpsichord and, less frequently, piano recordings.
I realized long ago not to trust my sonic memory, but it's difficult not to make some comparison with the past. I've heard Mini Disc in prototype form; I've heard first-generation players. They were adequate but sonically no match for CD. Obviously, things have changed with the Sony MDS 501. Call it second-generation, call it what you will, the MDS-501 sets a new standard for MD sound quality and is an absolute delight to use.
Edward J. Foster
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Portable Companion: Sony's MZ-E2
Sony sent an early sample of its second-generation portable player, the MZ-E2 ($549.95). Even with its rechargeable lithium-ion battery, it's amazingly small (3 inches deep, 3/4 inch thick, and 41/4 inches wide) and light (7.2 ounces). The lithium battery pro vides two-hour operation; it recharges in five hours (three hours for 80% charge) through the sup plied a.c. adaptor. It's also possible to operate the MZ-E2 from the adaptor and charge the battery simultaneously. The cell is removable, so you can switch to a fresh spare. A battery case (supplied), holding three AA cells, attaches to the back of the player; its cable plugs into the external power jack.
This battery case about doubles the thickness of the player. Alkaline batteries provide four-hour operation when used alone and 7 1/2-hour operation when used with the lithium cell.
Slide switches on the back of the player activate the Automatic Volume Limiter System (AVLS), to limit output to safe levels and choose either of two levels of bass boost (or none). A spring-loaded slide opens the disc slot. Nearby is a stereo mini-jack and a four-pin connector for the headset and remote controller. This controller, a small round pack with clothing clip, lies partway up the headphone cable.
You can control the MZ-E2 from built-in pads or from controls on the re mote. "Hold" controls on both player and remote lock the current operating Portable Companion: Sony's MZ-E2 mode. The buttons on the remote are small, but adequate if you're not thick-fingered. The controller carries two additional buttons not on the main unit.
One selects the play mode (normal, track or disc repeat, and random); the other cycles the LCD panel from indicating elapsed time on the current track, to a scrolling display of the track name, and to a scrolling display of the disc title. The track number appears in the first two cases; the total number of tracks on the disc comes up in the last case. The disc name and total number of tracks appear when a new disc is loaded. A battery condition indicator and play-mode symbols also appear in the display, as do indicators for volume changes. The display is reasonably legible for its size.
In the U.S., the MZ-E2 comes with an over-ear headset that I find infinitely more comfortable (and better sounding!) than the "button" earpieces supplied in Japan.
It also comes with a soft carrying pouch. The most interesting optional accessory is the CPM-MZE2K car mount kit, which (if I correctly interpret the manual) includes an umbilical cord, to power the unit from the cigarette lighter, and a connecting pack that couples the output of the MZ-E2 to the cassette heads of a car head unit. An external a.c. power adaptor and battery charger (ACP MZ60A) and additional lithium-ion batteries (LIP-10) also are available.
I didn't run bench tests on the MZ-E2, but I did give it a go around the block. Pretty impressive. Even in rough use, the deck didn't skip a beat.
(Presumably, the laser head mistracked on occasion but recovered before the 4-second buffer ran dry.) Sound quality was easily up to the best Walkman standard and was far and away superior to garden-variety portables. I didn't find the headset particularly comfortable (but neither was it uncomfortable), and I wasn't blown away by its deep bass response. There was enough upper bass to give the impression of a solid low end, however, and headphone comfort is inherently personal. I heartily approve of the AVLS concept, but I think Sony has been overly cautious. The sound level with AVLS on is just louder than good background-music level, and people who need AVLS protection the most are likely to turn it off!
E.J.F.
(Source: Audio magazine, Nov. 1994)
Also see:
Denon DMD-1000 MINIDISC RECORDER (Dec. 1998)
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