Manufacturer's Specifications
Frequency Response: 5 Hz to 20 kHz +0.5.- 1.0 dB.
Dynamic Range: Greater than 90 dB.
S/N: Greater than 90 dB.
THD: Less than 0.01%.
Separation: Greater than 80 dB at 1 kHz
Output Level: Fixed, 2.0 V rms: vari able, 0 to 2.0 V rms
Number of Programmable Se lections: 15.
Average Access Time: 3 Sec.
Power Requirements: 120 V a.c.. 60 Hz, 49 watts.
Dimensions: 16.9 in. W x 3 in. H x 12.6 in. D (43 cm x 7.5 cm x 32 cm).
Weight: 11 lbs. (5 kg).
Price: $599.
Company Address: 222 Hartrey Ave . Evanston, Ill. 60202.
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One of the questions am asked most often when I give a talk about digital audio is, "How long will the laser diode of a CD player last?" There's no single answer, since not all laser pickups are of equal quality. It is of some significance, therefore, that Shure now offers a five-year warranty for laser replacement. They state that the laser diode used in the D6000, their latest CD player, will last for a minimum of 8,000 hours.
Fig. 1-Frequency response, left (top) and right channels.
Fig. 2-THD vs. frequency at maximum recorded level (0 dB).
Fig. 3-Spectrum analysis of reproduced 20-kHz test signal.
The D6000 certainly has plenty of features to boast about as well. Full 16-bit processing with two-times oversampling is combined with an effective digital filtering system that provides more than 80 dB of out-of-band attenuation. Gentle post-D/A analog filters are employed above 30 kHz in order to preserve phase integrity and tonal balance within the audio range. As is true of most higher quality, late-generation CD players, the D6000 uses a three-beam laser pickup.
which is said to do a better job of compensating for vibrations and disc imperfections. To ensure against future obsolescence, the designers of this unit have included a digital subcode output terminal so that when the long-awaited peripheral "black boxes" for graphics finally arrive, you'll be able to connect one to the D6000 and to your video screen.
As for user convenience features, the D6000 comes with a 19-function wireless remote control which has a 10-key layout for selecting and programming tracks. Up to 15 tracks can be programmed, in any order. You can even use the remote to control output levels to the variable output terminals or to the headphone jack. The front-panel controls as well as buttons on the remote let you perform an audible search at two speeds, in either direction, to find a desired point on a disc. You can also skip ahead or backwards from track to track, and quickly access any of up to 99 tracks by 3 using the number keys on the remote control. There are four repeat-play modes: Repeat of an entire disc, a track, a sequence of tracks, or a track segment. For those who simply want to play a disc from start to finish, there's automatic one-touch load and play. You simply load the disc and touch the "Play" button; the tray closes automatically. In short, Shure's D6000 incorporates just about every convenience feature you would want. The only feature that I found lacking was direct access to specific index points on a disc (when such index points exist). The multi-function digital display does indicate which index point within a given track is being played, however.
Control Layout
The "Power switch and disc tray are at the left end of the D6000's front panel. The "Open/Close" button to the right of the tray can be used during loading and unloading, but insertion and playing of a disc once the tray is opened can also be done by pressing the "Play/Pause" button. A multi purpose display area to the right of the "Open/Close" button provides a wide variety of indications including track and index numbers during playback, elapsed time from the beginning of the current track, repeat-play mode, memory cue (used during programming), and the number of the programmed selection. Additional indications illuminate to show that a disc has been loaded, that a disc is being played, or that the player is in the pause mode. Below the "Open/Close" button is a "Stop/Clear" button, and to the right of this key are buttons for forward and reverse scan, forward and reverse track skip, and "Play/Pause." By combining play and pause functions in one button and stop and program-clear functions in another, Shure has avoided the "busy" look common to some high-end, high-performance CD players.
Three small buttons arranged one above the other near the right end of the panel handle repeat programming functions and memorization of up to 15 track selections. At the extreme right end, a small rotary control adjusts level at the variable output terminals as well as at the headphone output jack located below the control.
Pushbuttons on the remote control duplicate all of the front-panel functions except power on/off, even including opening and closing of the disc tray. I'm not quite sure what practical purpose is served by being able to open and close the disc tray from the comfort of your easy chair, since you would have to get up to load a disc anyway (unless you are a basketball star or, better still, a Frisbee champ), but I guess this feature does no real harm either. On the other hand, being able to adjust volume from a distance is a very worthwhile feature. I have noticed that there are rather substantial differences in average level among CDs in my collection. Some recording engineers push maximum re cord levels right up to the highest bit available, while others seem to prefer to remain a bit (or a few bits) below that maximum allowable level.
Fig. 4-S N analysis, both unweighted (A) and A-weighted (B).
Fig. 5-Separation vs. frequency.
The rear panel of the D6000 is equipped with the fixed and variable pairs of output jacks mentioned earlier, and with a multiple-pin connector identified as the subcode output terminal. Concerning this extra connector, the owner's manual simply states that it is "for future use of video image subcodes, i.e., video signals recorded on the Compact Disc along with audio signals." No mention is made of the fact that to view such future graphics you'll need some sort of an add-on box, but that, of course, is the case.
Measurements
The advantages of digital filtering and two-times oversampling were apparent even from my measurements of audio frequency response. Since the output analog filter's cutoff point could now safely be moved up to 30 kHz, response was flat within ±0.4 dB to 20 kHz for both channels, as shown in Fig. 1. Harmonic distortion at maximum recorded level was just under 0.005%; more important, it remained at that low, low level over most of the audio range, as shown in Fig. 2. As usual, the dotted-line .extension shown in the region above 10 kHz in Fig. 2 does not represent harmonic distortion. Rather, it arises from the presence of a single inaudible "beat" above the audio band, as illustrated in Fig. 3. Unlike the results obtained with poorer quality CD players, this beat, occurring at around 24.1 kHz when a 20-kHz test signal is reproduced, is of relatively low amplitude. Nor is it accompanied by other in-band or out-of-band spurious outputs which have been commonly observed on CD players of lesser quality.
If I had followed the recommendations of the EIAJ and had employed a 20-kHz low-pass filter when making these distortion measurements, THD would have remained around 0.005% over the entire range of frequencies measured. It is my feeling (and that of the EIA committee which has been laboring to come up with a more meaningful CD measurement standard) that out-of-band spurious products should not be obscured by the addition of a low-pass filter in the signal-measurement path.
Figures 4A and 4B show the analyses of unweighted and A-weighted signal-to-noise ratios for the D6000. The un-weighted S/N measured a very high 97.7 dB (which is as high as the weighted figure I have obtained for many CD players), and the A-weighted S/N was an outstanding 102 dB below maximum recorded level. Dynamic range (the difference between maximum [zero] recorded level and the THD amplitude for a 1-kHz tone at-60 dB) was an equally superb 102 dB. Linearity was nearly perfect all the way from maximum recorded level (nominal 0 dB) to- 80 dB. De-emphasis, when activated by a disc which had been re corded with pre-emphasis (only a few discs make use of this additional noise-reduction technique), was accurate to within 0.3 dB over the entire audio frequency range. Since both the EIAJ and the proposed EIA CD measurement standards call for a test of wow and flutter, I went through the motions of trying to ascertain this parameter. If there was any flutter, it was too low for my test instruments to read.
SMPTE-IM distortion measured less than 0.01%; CCIF IM was even lower, with readings of 0.004% at maximum re corded level and 0.003% at-10 dB recorded level.
Fig. 6-Reproduction of a 1-kHz square wave.
Fig. 7-Single-pulse test.
Fig. 8-Interchannel phase comparison at 20 kHz. Absence of interchannel
phase error is indicated by 45° angle of Lissajous pattern on 'scope.
Stereo separation, plotted in Fig. 5 as a function of frequency, was close to 85 dB at mid-frequencies, decreasing to a still very high 71 dB at the treble end of the spectrum.
Maximum output level from the player was 2.50 V, and the difference in output between channels was only 0.03 V.
Short-term access time (the time it takes for the laser pickup to move from one track to the next) was no more than 1 S, and long-term access time (the time it takes to get from an inner track to an outer track) measured approximately 6 S.
A 1-kHz square wave, as reproduced by the D6000, is shown in the 'scope photo of Fig. 6. It is as close to perfect as I have seen from any CD player. The departure from a perfect "flat top" in the reproduced waveform is due almost entirely to the absence of higher order harmonics and not to any "ringing" or overshoot that might be present if steep analog low-pass filters had been used. The impulse signal shown in Fig. 7 further confirms the fact that excellent digital filters have been used in this player.
Figure 8 reflects my new method of measuring time delay or phase error between left and right channels. Instead of superimposing two 20-kHz sine-wave signals from the two output channels, I now apply the output of one channel to a 'scope's horizontal (X-axis) input and the output of the other channel to the vertical (Y-axis) input. If the signals from both channels are perfectly in phase, the screen should show a straight line tilted 45° from lower left to upper right-which, as you can see from Fig. 8, is exactly what it did show.
Use and Listening Tests
The D6000 zipped through my old defects disc without a single glitch or moment of mistracking. What's more, it operated flawlessly even when tilted at angles that were not recommended by the manufacturer. The unit was also very resistant to external shock and vibration. I had to tap its sides and top far harder than anyone is likely to do in actual use before any muting took place. When I finally did upset the player enough for it to mute, play resumed, after the momentary mute, very near the spot where it had been interrupted.
A more important test, of course, is how the D6000 sounded when reproducing some of my favorite CDs. In a word, it sounded great! There was none of the abrasive raspiness I've heard from low-priced players when playing the same discs. Bass reproduction was awesome and full-bodied.
Transients were reproduced without a trace of hangover.
Quiet passages of music did not suffer from the kind of distortion that I have heard from players that use inferior digital-to-analog converters whose linearity near the least significant bits left something to be desired.
It is to Shure Brothers' credit that, as a major phono cartridge manufacturer, they have had the foresight to move into the world of digital audio in anything but a perfunctory manner. Their D5000 CD player was a good first effort. The D6000 surpasses that earlier player in almost every way.
What the two units do have in common is the excellent and very logical front-panel layout that makes operation almost self-evident even if you fail to read the owner's manual.
What sets the D6000 apart from the earlier model (and from much of the low-cost competition) is its superb sound reproduction and its stable tracking mechanism.
With the addition of the D6000 to their line of "Ultra" products, and the continued success of their HTS5000 surround audio processor, Shure shows every indication of remaining a vital force in the world of digital audio-just as they have been for more than 60 years in the world of professional and home analog audio.
--Leonard Feldman
(Source: Audio magazine; Nov. 1982)
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