What makes a CD Player Professional? (April 1984)

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by Leonard Feldman


above: The Denon DN-3000F Professional CD Player

When Denon America, Inc. announced that they were producing a "professional" Compact Disc player, those of us who had some experience testing and using CD players wondered what Denon could possibly incorporate into their CD player that would make it "professional" and particularly suited for use in broadcast and recording studios. After all, the 90-dB or more dynamic range offered by any CD player was a good deal more than even the best FM stereo radio stations could transmit using their existing transmitter and studio console equipment. The typical distortion figures of 0.005% or better were far lower than even the finest home FM tuner could boast. And, as for, programmability and easy access (a must for the radio DJ in the future CD era), many of the consumer-type CD players I had tested already exhibited sophisticated systems for such convenience features. What, then, would constitute a "professional" CD player? The answers soon became apparent when a representative of Denon drove up to the lab, hauled out a huge car ton, mounted it on a hand truck and wheeled it into my testing room. When the outer trappings were removed, I saw a 100-pound console measuring about 32 inches high, 16 1/2 inches wide and 22 inches deep. Taken aback by the size and weight of this "Compact" Disc player, I posed the big question to the Denon representative, "How does this CD player differ from all other CD players?" He explained that, ideally, such functions as slip-cueing, level metering, fade up, internal monitoring, balanced line out put, as well as protection features (which insure against inadvertent line feeds when they are not desired) should all be incorporated in a pro player. In other words, it should have the same access and cueing capabilities as a pro reel-to-reel deck. Denon's DN-3000F is just such a pro unit and, in fact, it incorporates several addition al features which arise from the CD disc format itself. They will be much appreciated by the studio engineer who, sooner or later, will have to start using CDs for background music in more complex productions, and for mix-downs as well as for dubbing.

The DN-3000F is, as I already mentioned, supplied as a stand-alone con sole, with controls and disc compartment located at convenient desk height. Discs are inserted into the player near its rear, via a top-loading mechanism whose door pops open when an eject button is depressed on the console.

Control Layout

"Running Address" and "Time" LED displays on a sloped section of the console are located near a pair of standard VU meters. Track number of the disc, index number (if encoded on a given disc to divide longer selections into smaller sections), and time (in minutes, seconds, and frames) are all displayed here. Three different time displays can be accessed, using a "Time Mode" button nearby. These are elapsed time of the track being played, amount of time remaining on the track being played, or absolute time from the beginning of the disc to the current position of the laser pickup. A second display, called "Order Address," is used in conjunction with a 10-key pad to provide elaborate random-access capabilities, including almost instant location of a given point in a disc, down to the very second and frame.

After punching in the desired track number, minute, second and frame, touching the "Locate" button brings the pickup to the desired location.

Touching the "Play" button then starts disc play, providing that the "Line Out" lever is in its "On" position.

Two more touch buttons near the numeric keypads are labeled "Slow-Fast" and "TOC." The "Slow-Fast" but ton is used in conjunction with a rotating "Search" dial, which is very much analogous to "slip-cueing" as done on a conventional turntable. The "Search" dial, which works very much like a cueing dial on a video console, allows you to move the pickup in frame-by-frame increments, quickly or slowly (depending upon which end of the "Slow-Fast" switch is touched). The pickup plays a single "frame" over and over again, allowing the operator to zero in on the precise cue location desired. The last button in this area of the panel, la belled "TOC," is a "Table of Contents" button which, when pressed several times in succession, causes the "Order Address" display to show first and last track numbers, total elapsed time, and starting time for each track.

Close to the front of the console desk, and handy to the operator's fingers, are a master output attenuator control, "Play" and "Pause" buttons, a "Monitor" on-off switch (which lights up when on), a separate level attenuator for the small built-in monitor speaker (which plays a "sum" program of L+ R), and a button labeled "Att(enuator) Start." This last-named pushbutton enables the operator to introduce start delays of from 0.1 to 0.3 seconds, or no delay at all. The operation of this function is somewhat similar to that found on professional turntables. The amount of delay for this function, as well as the length of play for the slip-cue function using the "Search" mode, is an internal adjustment normally per formed once during installation of the console player. "Standby" and "Line Out" lights above the VU meters tell the operator the status of the line out put signal. A cue light, just above the left-hand VU meter, lights when an external remote control is used with the player. Protection against possible operator error is built into the unit. For example, when the "Line Out" key is "On," the "Eject," "Locate," and "Search" controls have no effect if they are depressed or rotated.

XLR 3-pin connectors are located at the rear of the pedestal or stand which supports the player console. Cables connect to these connectors for balanced line outputs (separate left and right) and for a "Mix" input, which can be a signal from other equipment that can then be mixed with the CD signals and fed to the line output.

Measurements

Though the purpose of this investigation was not to treat the Denon DN 3000F as the subject of a full-length test report, I could not resist measuring the basic performance of this pro unit.

In terms of lab measurements, the unit performed about as well as a consumer or home-type CD player, which was no great surprise. Frequency response was virtually flat from 20 Hz to 20 kHz, with a slight rise of around 0.7 dB showing up at the high end before response dropped off sharply above 20 kHz.

Harmonic distortion at maximum re cording level (0 dB in terms of the digital recording, +4 dBm on the out put meters of the unit) was 0.004% at 1 kHz, rising to around 0.018% at the treble end of the spectrum, and 0.006% at bass frequencies. As is true of all digital disc players, at lower levels, distortion rises. At -24 dB levels, it measured 0.04% at mid-frequencies and around 0.06% at the ends of the spectrum. Linearity was accurate to within 0.5 dB from 0 dB down to below -80 dB, while unweighted signal-to noise ratio (band-limited to 20 kHz) was 93 dB below maximum output levels. SMPTE-IM distortion measured a low 0.01% at maximum output, in creasing to 0.08% relative to a- 20 dB IM test signal.

Square waves and unit pulses, contained in the special Philips test disc that I now use to test all CD players, looked just about the same as they did when I tested all the home players that utilize sharp "brick-wall" analog low pass filters following D/A conversion.

There was the usual ringing at a super-audible frequency apparent in the re produced 1-kHz square wave, as well as the usual overshoot in both polarity directions for the unit-pulse waveform.

As for phase error, I calculated a time delay of about 25 ┬ÁS introduced by the low-pass filters, or about one-half cycle of a 20-kHz signal.

As for the Denon DN-3000F's ability in the area of error correction, I used another test disc supplied by Philips which contains the defects likely to exist on a typical, improperly cared for disc. The defects consist of a wedge, which widens from track to track of the musical selections contained beneath it, a series of opaque black dots of increasing diameter, and, near the outer rim of the test disc, a semi-opaque smudge. The wedge is meant to represent a severe scratch on the surface of a disc, the dots to simulate dust specks (of varying size), while the "smudge" approximates a fingerprint on the surface of a disc.

The Denon DN-3000F was able to "track" the wedge until its width had increased to 600 microns. This is not particularly outstanding, since I have tested consumer-type players which can successfully play through that wedge at its widest point of 900 microns. The player did much better with the simulated dust particles, coasting right through the largest of them with out so much as a millisecond's worth of sound muting or mistracking. It wasn't at all bothered by the fingerprint simulation either. This suggests that professional users of this type of player should exercise the same care with respect to the surfaces of Compact Discs as they do (or should) with conventional LPs. They should be handled by their outer edges, and care should be taken not to allow their surfaces to become scratched. Given such care, the life of a Compact Disc will be as long as its promoters are claiming for it. Without this care, discs can mis-track, just as surely as poorly treated LP records can.

Use and Listening Tests

What makes the Denon DN-3000F unique is its superb solutions to problems that will face the professional studio engineer when he or she begins to use CDs in the course of normal broadcasting and mixing activities.

The very unit I tested, incidentally, was shipped from my lab to FM radio station WNCN, where it replaces an earlier consumer-oriented player made by Denon as well. In my own auditioning of the DN-3000F, I was especially de lighted by one feature of the unit which wasn't even described in the temporary owner's manual. When you insert a disc into the player's turntable area and close the door, the disc is automatically scanned so that track count, time counts, etc. all are stored in its computer memory. So far, that's not unlike some consumer players I've worked with. But the DN-3000F, in stead of coming to rest at the 00:00 starting point of the first track, actually cues up at the instant the music starts.

Thus, if the music on track 1 starts 1 second and 3 frames past the actual start of track 1, that's where the laser pickup will focus. Then, when you shift the "Line Out" lever to "On," music starts instantly-with absolutely no waiting. That, and the other remarkable cueing and random access features of this player, make it worthy of the designation "professional"-a term that Denon never uses lightly.

Another important aspect of the player's performance, which is difficult to measure in quantitative terms, is its ability to withstand physical shock and vibration. Unlike some consumer CD players which I've tested, that mistrack even if their cabinets are tapped lightly with a finger tip, the Denon DN-3000F continued to track flawlessly even when I pounded my fist on the con sole's surface, right near the "turntable" itself. Such refined and stable tracking capabilities must involve mechanics and servo mechanisms that are far costlier than those used in home CD players. The special random access and display features also add to the final cost of the unit, as do the real VU meters (not found on any home players), balanced line outputs, and all the other features which distinguish this player from consumer versions.

Clearly, radio station WNCN in New York must have thought that the difference in features and performance was worth the extra $7,500 or so, or they wouldn't have traded their consumer player for this expensive model.

(adapted from Audio magazine, April 1984)

Also see:

CD Packaging-- A Boxing Free-for-All (Feb. 1992)

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