The Tables Have Turned!

A Revolution in turntables may be an easy pun, but it aptly describes what is happening (and what is about to happen) in a major area of home entertainment. The innovation, which is still waiting in the wings but threatens to come onstage at its own cue, is digital sound. Why the fuss? According to Sony, which has been working on digital-audio-disc systems since 1976 and whose latest version--the model DAD-1X--is shown here, digital audio represents such an advance in the quality of recorded and reproduced sound over existing analog sound that its development is tantamount to bringing present-day audio "out of the Stone Age."

Digital sound (also called pulse-code modulated sound, or PCM) is credited with banishing all the forms of distortion inherent in analog sound. Wow and flutter become ghosts of the past finally laid to rest. Dynamic range is increased to 95 dB or more as against the 50 to 60 dB of the best analog discs. Frequency response is ruler flat across the audio range up to 20,000 Hz within a mere +0.25 dB variation. (For all you nontechnical buffs, that's terrific.)

That kind of performance from a disc recording involves, as you might expect, a radically new kind of record and player to handle it. Basically, the system is a spin-off of video-disc technology, and so a few companies other than Sony also have prototypes or at least working models that are let out tentatively from the labs for a peek by the press and audio trade. The Sony model, like many others, uses a laser beam to scan the digitally pulsed signal on the specially coated disc. There is no physical contact between the record and a tracking stylus. That factor alone does away with record wear, tracking distortion, stylus wear, stereo-channel lopsidedness and other deviltries, not the least of which is the static charge that attracts dust.

As a final fillip, the Sony system, which runs at a speed of 450 rpm, can pack up to two and a half hours of playing time on the one-sided disc, enough for many a full opera or a hefty rock concert, depending on your musical tastes.

Before rushing out to queue up at your local hi-fi dealer, be advised that none of the impending systems is currently in stock. Nor is any likely to be available for some time. Estimates as to just when vary from five to ten years.

The reason for the delay is not that technology or production know-how is lacking but that the records themselves are. The PCM trend is still essentially a hardware-inspired thrust, based largely on the audio possibilities inherent in a digitally encoded video disc. In that regard, it is unlike two earlier major changes in record playing--the long-playing or microgroove disc in the late Forties and the stereo disc about ten years later.

Both of those upheavals started in the recording industry itself; and, in each instance, it was a matter of hardware's following the new software, or new equipment's being developed to play the new kind of records. The digital disc, or at least the audio digital disc, has not been announced as a new home-program format by any recording company. It is, in a sense, being thrust on the recording companies--and at a time when they are attempting to cope with a slew of problems, from the rising cost of vinyl to shaky sales.

As for digital sound as such, the record companies are just getting into it by using digital tape recorders for making master tapes, which then are used for cutting and processing conventional analog discs. And even here, there are reports that the exact digital tape system to use can become a source of violent internal controversy among top recording executives, producers and performers.

In the meantime, today's turntable remains a viable product, and the sheer number of new models--not to mention the improvements and refinements associated with them--seems ample testimony to the continued durability of records as we know them. There have been changes within that format, but they are evolutionary, not revolutionary.

Record-buying and record-playing habits seem to be somewhat related to what has happened to turntables (and their working partners, tonearms and cartridges) in the past few years. What has happened, of course, is the rise of the single-play turntable and the decline of the platter-plopping automatic model. One reason for its success is the indisputable logic contained in the argument: Why pay for automation that you don't use?

One of the first of the Seventies' examples of the "economy manual" was the Pioneer PL-12AC, a two-speed model (33-1/3 and 45 rpm; the 78-rpm speed was summarily dropped as of no further interest to the current market) that sold in 1972 for a mere $100. A year later, hi-fi enthusiasts were attracted to a unit that had an even more intense appeal in aficionado terms. That model was the Technics SL-1100A, also a two-speed manual but costing (with mounting base) $350. That price got you no automation, but it did get you state-of-the-art performance. It also--in common with other Technics turntables that soon began proliferating--reintroduced to Seventies hi-fi fans the phrase direct drive, which, together with other buzz words such as quartz locked and radial tracking, have become the new jargon for today's turntables.

Direct drive suggests, of course, indirect drive, which is actually how most turntables operated and how many still do. The indirect-drive turntable uses a high-speed motor whose normal speed--usually about 1800 rpm--must be reduced to the 33-1/3 or 45 rpm required by most records. The speed reduction, and the coupling of the energy to the rotating platter, can be handled by an idler wheel or a belt. Because idlers tend to develop flats, and because they do not isolate the platter as effectively as belts, the belt-drive system became the preferred choice for hi-fi applications.

A direct-drive turntable uses a motor that rotates at the same speed as the platter, and coupling is literally direct, since the center spindle over which you place the record is an extension of the motor shaft. By definition, the slower a motor turns, the lower in frequency will be its rumble, which is all to the good. However, the control of such a motor--especially for the critical job of rotating a record--requires some fancy new technology, such as servo control or the even fancier one known as quartz locked in which a quartz crystal serves to "monitor" the speed and initiate any needed correction instantaneously (not unlike the quartz control used in watches). Generally speaking, the cost of a quartz-locked-control turntable will be higher than that of a servo-controlled unit, which, in turn, will be more costly than a belt-drive unit. To be sure, design features other than the drive system (such as the weight of the platter and the type of arm used) contribute to the varying costs, but the over-all pattern is illustrated by these examples.

Yet another refinement on the quartz-locked direct-drive system is the quartz-locked double servo system, which has both a frequency generator and a circuit known as the phase locked loop (PLL). The PLL is designed to enhance speed accuracy by freeing the turntable from small speed drifts caused by changes in temperature, load or voltage. In the new Yamaha YP-D71, for example, the PLL feature is incorporated by means of an integrated circuit.

Despite the increasing popularity of direct drive, a healthy quota of belt-drive turntables continues to be manufactured and enjoyed by a vast number of hi-fi listeners. But the newest versions are belt drive with a difference. For example, in the Philips AF-977, the motor is coupled to the platter via a belt, but a tachometer monitors the speed and signals any needed corrections through a PLL circuit. Philips calls this system Direct Control. In the new belt-drive Visonik VT-5300, the motor is servo controlled with the help of an internal frequency generator. Again, speed is constantly monitored and any needed adjustments are immediately made.

The obvious concern with speed control (by whatever means) has less to do with the actual absolute speed as such than with those small, nagging short-term speed variations known as wow and flutter. Those slow and rapid, respectively, speed variations can distort the musical sound by introducing wavering pitch or birdies into it. No less disagreeable, and potentially more harmful, since it can introduce heavy distortion and overload into a stereo system, is the low-pitched noise known as rumble. While the direct-drive system starts out with potentially low rumble, this virtue is hardly its exclusive accomplishment. Properly made belt-drive systems have inherently low rumble, too. It is, in the last analysis, a matter of how well any operating principle is applied and worked out in terms of the parts used and how cannily they have been assembled.

The moral is not to let any buzz word con you into buying a product that cannot document its own performance in terms of hard specifications. A typically fine spec for wow and flutter (the two disorders are usually combined into one measurement) would be a weighted root mean square (WRMS) of about .03 percent, and the lower that number, the better. A good rumble figure would (concluded on page 286)Turned Tables(continued from page 136) be --60 dB weighted or a number more negative than that; say, --65 dB. Sometimes, rumble is expressed as a turntable's signal-to-noise ratio, in which case it becomes a positive number; this time, the higher the number, the better (e.g., 75 dB is quieter than 70 dB). Note that all specs must be derived from the same measurement system to offer meaningful comparisons.

One very important feature of a turntable that is not given by the numbers, but that can make a major difference in a turntable's suitability in certain systems, is the method by which its internal parts are suspended under the chassis top. That particular factor has become virtually critical with the continuing burgeoning of the so-called superdiscs (the direct-cut types, the digital-tape processed albums, the dbx-encoded releases and the records that are produced by several labels with more than the usual lavishing of tender loving care). Those records offer an enhanced dynamic range that can trigger acoustic feedback from turntables that never before suffered from that noise. Sometimes, placing special feet under the turntable can help, but the real cure lies in the machine's internal suspension. It must not be too stiff. That doesn't really say a hell of a lot, but it's something to ask about when you're contemplating spending a few hundred bucks on a new turntable on which you hope to play any new record that comes along.

A closely related feature is the tone-arm and the cartridge fitted in it. The key concept here is low mass and its concomitant benefit in reducing the resonance between the arm and the cartridge. In general, the arm supplied as an integral part of a given turntable can be counted on to represent an optimum mating with that turntable, at least from the standpoint of the product's designer. But note that what looks good to, say, Pioneer or Technics--both of which favor the bent, or "S-shaped," arm--does not get the nod from Thorens, which uses a straight arm with a slightly offset head. How's a body to know? I don't believe you can tell merely from the arm's shape. If you get to that kind of critical crossroads in your decision about which unit to buy, you would do best to listen to both fitted with the same cartridge playing the same record.

Two recent trends in tonearms are worth mentioning. One is the integrated arm and cartridge, those two elements being designed for each other in a mutually exclusive relationship. The Danish firm of Bang & Olufsen has long espoused that approach; more recently, it has surfaced in the Dual ULM (for ultralow mass) series in which a new tonearm is mated with an Ortofon-made pickup designed especially for it.

The other news in arms is the sudden increase in the number of true radial arms. Instead of pivoting from one end, these arms move the cartridge across the record in a straight line, the same radius with which a record is cut. Known also as tangential tracking, this system is credited with eliminating the small angular error that must perforce occur with a conventional pivoted arm. Whether or not you can hear the difference may be a moot point. Less debatable, however, is the fact that a radial arm does away with the need for antiskating compensation, since the skating problem arises in the first place as a direct consequence of an arm's being pivoted. A well-designed radial arm probably also will permit you to use a given cartridge at its lowest possible vertical tracking force, which could prove (over some years, anyway) to help extend the longevity of your records. Among the companies recently offering radial arms are Phase Linear, Technics, Aiwa and Revox.

Having bestowed most of its recent technology on the single-play turntable, a portion of the industry is embellishing that product with a new kind of automation. Optonica, for example, has announced a turntable with a built-in microprocessor that can be programmed to play not only individual bands of a record but also portions of bands. A digital readout system also tells you what has been programmed and what part of the action is going on. Digital readout of speed also is featured on several brands, as well as very smooth cuing controls for setting the stylus onto the record and lifting it off at the press of a button.

Fillips like those do nothing to help the sound of your records, but they can make playing them perhaps a little more intriguing than in the past. With or without them, it seems fairly certain that on today's turntables, your records never had it so good. In fact, they may sound so great that you may find yourself asking: Who needs digital sound, anyway?

"Superdiscs offer an enhanced dynamic range that can trigger acoustic feedback from turntables."