WHAT'S COMING UP?
IN a little more than the three decades since U.S. Army Signal Corpsman John Mullin "captured" three German Magnetophon recorders, the tape industry has gone from birth to a vigorous maturity, and it's worth pausing this month to try to see just what is (or may be) coming up on the tape horizon.
Six years ago this month the editors of STEREO REVIEW asked me to design--on paper--my "Dream Machine," and it has been a source of great satisfaction to me ever since to watch one after another of its features (of ten much improved upon) progress from the studio or drawing board into the world's listening rooms.
Cassettes have now, of course, come to dominate all but the high end of the tape market (in terms of both dollars and frequency response), but their position is about to be at tacked on two fronts. "Microcassettes," smaller than matchboxes and running at only 15/16 ips, have been developed, and before long you may be able to put all of Mozart's symphonies into the glove compartment of your car-along with the machine to play them on. (The micro-cassette should not be confused with another miniature cassette dictation system, the minicassette, which has a variable-speed drive system that makes it un suitable for music recording or reproduction.) From the opposite direction, a number of manufacturers have concluded that the cassette format, with its rigid licensing restrictions, has been developed about as far as it is economical to do so, and they have decided, further, that its performance simply is not going to satisfy the critical home listener/recordist. Historically, 7 1/2-ips open-reel tape has been the choice for serious music recording, and attempts to sell 3 3/4 ips as "just as good for half the tape price" simply failed. But per haps in bypassing the 3 3/4-ips speed entirely, the downward speed shift of the cassette for mat did go just a bit too far.
Such, at least, is the thinking behind the new elcaset format, announced some time ago and shortly to be introduced (if promises are kept) in actuality. Twice the speed and a wider track width will give the elcaset--it is still only about the size of a paperback book significant advantages in frequency response and signal-to-noise ratio over its smaller cousin. No less important, though the convenience of no-threading operation is retained, is the fact that in the elcaset system the tape leaves the shell entirely, so the advantages of an open-reel deck (stable and precise tape drive and guidance) will be retained. And, of course, three-head operation will be the norm, not the exception.
Poor open reel! The elcaset, if successful, will knock out the little that is left of its attractiveness in the "under $1,000" market. But, for absolutely state-of-the-art professional and semiprofessional applications, open reel, has been, is, and will continue to be supreme, and the continuing attention paid to its development will, as in the past, be the primary (though by no means exclusive) source of the fundamental improvements that find their way into home tape systems.
LOOKING at the state of the reel-to-reel art today, one of the immediately obvious areas of development is in the design of tape-drive mechanisms that will more nearly do what a transport (in its "play" mode) is supposed to: move the tape across the heads at an accurate, unvarying rate. The central point in the system, of course, is the rotating capstan, and in older designs it was driven through a series of rotating rubber wheels pressed against the shaft of an induction motor whose speed varied somewhat with the voltage of the a.c. line. That rather crude system gave way to the belt-driven capstan run by a motor synchronized to the 60-Hz frequency of the power line. And now that, in turn, is about to give way to the capstan directly driven by a d.c. motor whose relatively slow rotation is synchronized, through a phase-locked servo-control, to an ultra-stable quartz-crystal oscillator. The improvement this system affords in long-term speed accuracy is of little consequence to the home user, though it is vital to, for example, the broadcaster. But the very considerable improvement in short-term speed accuracy (elimination of wow and flutter) is an enormous benefit to recordists.
Tape-motion aberrations do not all arise from the capstan's rotation, however. What happens at the supply reel (and, to some ex tent, the take-up reel as well) also affects the motion of the tape against the heads. In recent years, many recorders, both open-reel and cassette, have adopted a "dual-capstan" sys tem that isolates the portion of the tape passing across the heads from the action of the supply reel as well as the take-up reel. That's a step in the right direction, but it sets up two rotating capstan and pressure-roller systems, each of which can introduce wow and flutter of its own.
The next step, used in 3M's Mincom professional recorders (and appropriated into my "Dream Machine"), has now been taken, with a variation or so, by one major manufacturer of nonprofessional recorders. This involves feeding the tape between the pinch-roller and a very large-diameter capstan, down past two heads, then around another large-diameter idler, back up past two more heads, and finally squeezing it with a second pinch-roller against the opposite side of the same large-diameter capstan. This single-capstan, isolated-tape-loop system is an example I expect other manufacturers will follow in time.
With either type of closed-loop system, single or dual capstan, the isolation from the sup ply and take-up reels that is provided by the pinch-roller action is never complete, how ever. And with conventional reel motors, the supply and take-up tensions vary directly with the amount of tape on each reel-a ratio of about 3:1, and in opposite directions from each other as well. Servo-control can, how ever, be extended to the reel motors them selves so that they, too, provide a constant tension regardless of the size of the tape pack.
This is standard professional procedure, and it is now coming into increasing use in top quality consumer equipment.
Once servo-control is applied to the reel motors, however, another possibility-actualized in the new professional Ampex ATR-100 series-is opened up. That is to eliminate the capstan puck rollers (themselves a source of wow) entirely, so that the large-diameter capstan doesn't drive the tape at all, but merely governs (via servo-control) its pace. This re quires that the reel-motor servo system be perfectly balanced-but with enough electronic sophistication it can be. I've used it, and it works magnificently-another example for top-end open reel (or elcaset) decks eventually to follow. The new Omega open-reel machine from Uher is the obvious forerunner of this trend in consumer equipment.
REVOLUTIONARY new developments in tape oxides could appear quite soon-but they won't. Research is well on into pure metallic (non-oxide) particles that could be used to bring about a 12-dB improvement in the signal-to-noise ratio, but no one yet wants to push it. Why? For one thing, the material, when exposed to air, "self-combusts" like something out of Mission Impossible. That isn't the real problem, however, for within the binder it would be completely stable. The real problem is what confronts all tape "improvements": compatibility with existing record ers. The metal-particle tapes would require far more bias than today's machines can sup ply-enough, indeed, that today's heads would become obsolete as well. Any time you "improve" a tape-adding to its high-fre quency performance or increasing its overall output-machines that worked perfectly well with the "old" tape have, at the least, to be readjusted or even (as with the metallic particles) redesigned. It'll come, but not yet. In the meantime, chrome may become a casualty to improved ferric oxides, which will themselves continue to evolve slowly.
And, on the far, far horizon, the day of digital recording is coming; I'll talk about that more fully in another column.
Also see:
TAPE QUESTIONS and ANSWERS--Advice on readers' technical problems
TAPE RECORDING--A professional shares his tips on how to do it right, JOHN WORAM