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By Herman Burstein
LOOKING BACK at the nearly 25 years that the tape recorder has belonged to the family of home entertainment devices, one can count numerous and wondrous advances. The tape machine one buys today in the range of about $300 to $1,000 is a remarkable instrument. But is it all one could ask for? Has the technology fully matured? Have all the features and conveniences been thought of? From here on can one essentially expect only more of the same? I doubt this very much, judging from letters to the TAPE GUIDE, from what the experts say, from my own experience, and from the momentum of technology.
I have not attempted to survey manufacturers as to the innovations they plan for the next several years. For one thing, I suspect they are unwilling to reveal the aces up their sleeves, that is, to tip off the competition. Mainly, though, I feel what the future holds is geared to the felt needs of the present. Therefore my thoughts about the future do not try to conjure up undreamed of marvels, but relate largely to problems of the present.
Even so, some of these thoughts may seem far out to some persons. Here I am reminded of a conversation I had about 10 years ago with the chief engineer for a tape manufacturer. He stated that audio tape then was just about as good as it ever was going to become in terms of extended treble response, low noise, and low distortion. Yet there have been substantial improvements in tape since that conversation. Hence I hope the reader, whether amateur or expert, will be charitable toward my expectations, far out as they may seem.
For the most part my thoughts concern open-reel tape decks, which are still the principal medium for high fidelity. But the reader can freely translate these thoughts into terms of cassette machines. So, following are ten possible developments to increase the happiness of the tape recordist.
A number of the better phonographs enable the user to rapidly check and adjust turntable speed. Strobe markings and a neon lamp permit a check for accurate speed. And speed may be adjusted over a useful range by such devices as a magnetic brake or a variable-diameter shaft. Why not something similar for tape machines? Some audiophiles with treasured tapes made on an old off-speed machine would like to play them on a new machine if the latter's speed could be adjusted. Individuals playing prerecorded tapes or exchanging tapes would like to have correct speed, or at least speed satisfactory to their ears. The meticulous user would like to be able to check whether speed stays correct throughout the reel. And so on.
I have in mind an improvement and extension of what is already with us.
Although a number of tape machines feature reversibility, few do so in a way that provides maximum usefulness.
Many of the reversible machines operate this way only in playback, not in recording. Yet to me the reversible feature has the most importance in recording, because the tape may run out in the midst of a prized and unrecapturable moment of the recording session. (I become all thumbs in trying hastily to reverse the reels, rethread the takeup reel, and put the tape in its proper path. Under this kind of stress, more than once have I put the base side of the tape against the heads.) In playback I am less unhappy about the reel running out, because I haven't lost any of the material I wish to hear.
Therefore I look forward to an increased number of tape decks that are reversible in recording as well as playback. The user should always have the option between automatic and manual reversal, so that the machine will not accidentally erase the tape as the result of inadvertent reversal in recording.
Automatic reversal in recording should be on a fail-safe basis, requiring the user to push a button or lever each time he wants automatic reversal. To guard against accidental erasure, perhaps a bell might ring and/or a light might flash on as the machine approaches automatic reversal.
So quiet now are all other components of a quality audio system that the tape deck looms prominently as the chief offender with respect to noise.
For a long time designers of tape decks have struggled hard to inch up the signal-to-noise ratio by a decibel or two. Tape companies have considered it a prideful accomplishment to produce a tape that-all other things remaining the same-has 2 or 3 dB less noise. The difference between excellent and good S/N has generally been a mere four or five dB or so. A high quality machine can achieve something like 55 to 60 dB S/N, compared with S/N or 65 dB and higher in their components.
Fortunately, today's technology points not merely to further reduction of tape system noise by a few dB, but to virtual annihilation of noise. Compression systems, such as those of Dolby and Burwen, portend noise reduction by at least 10 dB and possibly by as much as 50 dB.
To give an idea of what this is about, consider the tape system noise to be at 0 dB level. Assume the dynamic range-difference between the loudest and softest sounds-of the program material to be 50 dB. And assume the S/N ratio of the tape system to be 55 dB (quite typical for high quality home machines); that is, peak recording level (corresponding to maximum tolerable distortion) is 55 dB above the noise level. If the loudest material is recorded at peak recording level, then the softest material is recorded 50 dB lower, which is only 5 dB above the noise level. Hence noise is evident on soft passages, and even on medium ones if volume is moderately high.
However, if S/N could be extended to, say, 70 dB, then the softest passages would be a handsome 20 dB above the noise.
In view of the importance of noise reduction, let us briefly inquire into the basics of compression systems such as those of Dolby or Burwen. The Dolby, on low-level signals, supplies boost in recording and corresponding cut in playback. With the cut comes a reduction of noise due to the tape and tape deck electronics. Since this process takes place only for low-level signals--when noise reduction is most needed--there is no tendency to overload the tape in recording as the result of the boosted signal. For home machines, the Dolby system operates only in the treble region, where most noise lies. For professional equipment, the Dolby system operates in several audio bands.
The Burwen system compresses all signals, so that the dynamic range becomes, say, 10 dB instead of 50 dB. Therefore the signal can be recorded at a level 40 dB higher than before; and the softest passages are an additional 40 dB above the noise of the tape system. In playback, the signal is expanded, so that the dynamic range of 10 dB again becomes one of 50 dB, with the softest passages retaining their additional margin above the noise.
(This 40 dB extra margin is only illustrative; the actual margin could be less or more.)
Presently the tape recordist walks a tightrope in choosing the proper recording level: too high a level, and distortion is excessive; too low a level, and noise is excessive. Achievement of S/N of 70 dB or higher would greatly ease his task and would permit him to record material with greater dynamic range.
For example, the task of recording electric guitar, with its tremendous peaks, would be simplified.
Instant Location of Program Material
The index counter is a useful but only approximate device for finding the start of a desired selection within a reel of tape. By comparison, it is much easier to locate the exact start of a section of program material (visible band) on a phono disc, for example the beginning of a song. Perhaps a bit of ingenuity will eventuate in a more precise locating device for tape.
Front-Panel Alignment Controls
The high quality tape deck incorporates a variety of alignment controls to adjust some or all of the following: bias level, recording level, playback level, record-level indication, recording equalization (treble boost), playback equalization (bass boost), erase current, bias frequency, etc. Generally the manufacturer's philosophy has been to bury these controls well inside the chassis of the home tape machine to prevent the unversed user from fiddling with them. But not all users are unversed. In fact, many of those who purchase high quality machines are quite knowledgeable or on the way to being so. Many also possess equipment such as signal generators, a.c. VTVMs, and alignment tapes, permitting them to make the necessary alignments, particularly when shifting from one kind of tape to another. Such alignments, or realignments, become necessary as tape formulations change, as components in the tape deck change value with age and heat, etc. Also, many users like to experimentally learn the effects of changes in bias, equalization, etc. Perhaps we should keep in mind that the name of the game is not only "audio" but also "experiment." However, it is an awful pain to have to remove 10 knobs, 24 screws, 8 grommets, an awkward electrical interlock, and a chassis 1/16th inch wider than its cabinet in order to get at the alignment controls! Some manufacturers of home tape machines have been kinder to the user by putting the alignment controls, or at least the principal ones, at the rear of the chassis. But even this can be a pain if the tape deck must be moved in order to get at the back. My hope is that in the future all alignment controls will be readily accessible to the user at the front of the tape deck-perhaps concealed under a hinged panel for esthetic reasons and as notice they are not operating controls.
It would be quite simple to prevent the user from radically fouling up the alignments if the manufacturer would put knobs on all the alignment controls and mark with paint the original factory setting for each knob. Thus the user would have benchmarks enabling him to return to the original setting of each control.
Built-in Test Facilities
A quality machine already has a signal reading device: the VU meter, which provides readings in dB. If the machine is further equipped with several test tones-say 400, 5,000, 10,000 and 15,000 Hz-it then incorporates very useful built-in test equipment, which can be used to check or adjust bias current, equalization, recording level, etc. In today's state of the art, a several-tone signal generator can probably be constructed in the form of an integrated circuit occupying minimal space.
How might the user put such equipment to work? For one thing, based on the tape manufacturer's recommendation for each of his tapes at each speed, he could adjust treble boost so that, relative to the reference frequency of 400 Hz, it is at the appropriate level at, say, 10,000 and 15,000 Hz. For example, a tape manufacturer might specify that his tape works optimally at 7.5 ips when recording boost is 11 dB at 10,000 Hz and 16 dB at 15,000 Hz. Assuming the tape machine contains suitable switching facilities so that the internal signal generator and the VU meter are connected to the proper test points, the user could adjust recording boost to meet these specifications as closely as possible.
Next he could adjust bias current so that treble response in playback is as flat as possible, as measured by the VU meter. (We are assuming that the meter is truly a VU meter, with essentially flat response throughout the audio range.) He might then make fine touchups involving both treble boost and bias to achieve the flattest possible response.
Or, to minimize distortion, he might increase bias at the cost of a slight sacrifice in treble, say 3 dB down at 15 kHz instead of perfectly flat out to that frequency.
With alignment test tape, the user can adjust azimuth of his tape heads; azimuth is correct when the VU meter gives a maximum reading in playback.
With a frequency test tape, he can use the meter to check playback response, and he can touch up the playback equalization (if the machine contains such provision) for flattest playback response. By means of the internal signal generator he can check overall record-playback response at the available frequencies; then perhaps it might be nice to have a few additional frequencies, such as 50, 100, and 1,000 Hz.
Using the standard reference tone on a test tape, at which the VU meter should read 0 VU in recording--he can adjust the record-level indication as follows: play the test tape; note the VU meter reading; record the 400 Hz internal frequency on the tape to be used for recording; adjust recording level until the same playback reading is obtained as for the test tape; at this recording level, adjust the VU meter calibration to read 0 VU.
Peak-Reading Record-Level Indicator
So long as the recordist is caught between the horns of excessive recording level and excessive noise, owing to a limited S/N ratio, it is highly desirable to know when signal peaks are exceeding maximum permissible recording level (corresponding to maximum tolerable distortion). That is why I have long favored the electronic eye, which is a peak-reading device, over the VU meter, which is an average-reading device. And that is why it is the practice in a number of foreign countries to use peak-reading meters.
On the other hand, a meter that reads average signal level also has its advantages, for example in equating the levels of different sound sources or in making level adjustments of known magnitude. The best answer therefore seems to be to provide the recordist with both average-reading and peak-reading devices. For example, an electronic eye could be built within the case of a VU meter or it could be mounted atop or below the meter.
Possibly a meter can be designed with two pointers and two scales for average-reading and peak-reading.
Quite a few readers complain about their tape machines, particularly in playback, picking up nearby radio broadcasts-AM, FM, military, aviation, etc. It would be no great problem for home tape machines to include better filtering at the inputs of the recording and playback amplifiers to prevent such pickup.
Modular Components For Easy Servicing
Audiophiles often find it quite burdensome to go through the process of having their tape decks serviced. Often this involves locating a reputable service agency, lugging or shipping the machine to the agency, waiting several weeks or months for the machine to be serviced, and hoping the machine is cured of what ailed it-a hope too often unfulfilled. Use of modular components, perhaps some 8 or 10 modules for the electronics, could go a long way toward helping the user be his own serviceman. If separate modules are employed for each stereo channel, most of the modules would be duplicates, permitting interchange of modules between channels in order to identify a defective module. For example, if Channel A isn't recording but Channel B is, then substituting Channel B modules into Channel A, one at a time, is apt to turn up the defective module.
If modules can be kept to a low cost, say under $10 each, it might pay for the user to stock spare modules in the way he used to stock spare tubes.
I wonder how far the modular approach can be carried out in the case of the electro-mechanical portion of the tape deck, that is, the transport mechanism. Given hard thought to the matter, design improvements might be achieved which permit the user to at least make some repairs with ease, such as changing belts, brakes, idlers; adjusting tape tension; replacing heads; etc. In this age when good service is hard and costly to come by, it is to be expected that the machine of the future will be serviceable by the user to a higher degree than now.
Modem tape recorders pay much attention to the logic of their controls; that is, to be proof against the user making the wrong move which might break tape or accidentally erase a recording, and to minimize the number of controls and connections required to achieve a desired effect. It is to be expected that the trend will continue.
To illustrate, not all tape machines give adequate warning that the unit is in record mode; a panel lamp that glows when the machine is in record mode, and starts glowing before the transport starts up, is desirable. Not all machines make it easy to get into the sound-on-sound mode; some require special reconnection of cables.
Some machines facilitate feeding a mono signal into both outputs of the unit, while others don't. With some decks it is easy to record on one channel while playing the other, and with other decks it is difficult or impossible.
(adapted from Audio magazine, Apr. 1972)
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