TAPE GUIDE (Jun. 1986)

A Tape for All Players

Q. My primary tape deck has both Dolby B and C noise-reduction systems, while the tape players in my cars have DNR (Dynamic Noise Reduction) but not Dolby B or C NR. I also have a personal stereo player with Dolby B NR. Using my primary deck, I want to make a single tape that can play back satisfactorily on all my decks. How can I best do this?

-Robert A. Nuernberg, Mequon, Wisc.

A. I suggest that you make your recordings .with Dolby B NR. When played back without Dolby decoding, they will sound a bit bright but not unreasonably so; this added brightness may even be desirable in the environment of a moving car. If the brightness is undesirable, a mild downward turn of the treble control will help. Another strategy is to use Type I (ferric oxide) record EQ and play back with Type II EQ; this will provide a moderate treble cut.

Checking Dolby Alignment

Q. I own a home cassette deck with Dolby C NR, which I use to make recordings that I play on my Sony Walk man, which also has Dolby C NR. The first time I made recordings and played them back on the Sony or several other cassette decks, they sounded muffled and lacking in highs. There was also audible pumping of the sound as the Dolby C NR switched the playback levels at obviously incorrect points. Recordings made and played back on the home deck sounded fine.

On the other hand, professionally re corded tapes with Dolby C NR sounded fine on other equipment, but not on the deck in question.

I have made test recordings on the deck, using Dolby 8 NR and no NR, and these recordings are compatible with other equipment. This eliminated azimuth misalignment as the cause of my problem. I believe that the fault lies with the deck's Dolby NR calibration, so I sent the unit back to the manufacturer. The deck was returned to me improved, but still not totally compatible with other equipment. Is there any way that I can determine if my cassette deck is adjusted correctly, once and for all?

-Robert A. Ward, Cleveland Heights, Ohio

A. To check your deck's Dolby NR alignment, you need a test tape containing a 400-Hz tone at Dolby level (200 nWb/m) and a signal generator that produces a 400-Hz tone. First, play the test tape; the meter of your deck should indicate Dolby level. Next, record a 400-Hz tone on your own tape at a level that drives the indicator to the Dolby mark; when playing this tape, the indicator should again come to the Dolby mark. If playback of the test tape does not produce a Dolby-level reading, or if recording at the Dolby mark does not produce a Dolby-level reading in playback, your deck is mis aligned.

High-quality Dolby-level test tapes are expensive. If you have access to a cassette deck that you trust to be properly calibrated, you can make your own Dolby test tape with probably sufficient accuracy to be useful. Re cord a tape at Dolby level as indicated by this deck's meter, using a 400-Hz tone from a signal generator or per haps from a test phono disc. When this tape is played on your own deck, your deck's meter should read Dolby level.

Deck Incompatibility

Q. I own two cassette decks, a JVC KD-V200J and a Technics RS-814. When I record on the JVC with high-quality tape, using Dolby C NR, the playback on the JVC sounds superb. But when I play this cassette on the Technics, the high end sounds muffled. Also when I record on the JVC and play the tape on the Technics, the right meter is about 2 or 3 dB down relative to the left meter, and the right channel seems to have more bass than treble.

-Eric Gagne, South Hadley, Mass.

A. Apparently you have an azimuth alignment problem. That is, either the JVC or the Technics record/playback head, or both, are not correctly aligned. You may also have a Dolby NR tracking problem, which often results in treble loss. Again, one or other of the two decks, or both, may be at fault. The difference in response between the left and right channels may relate to the azimuth problem or the Dolby tracking problem, or both.

If the JVC plays its own tapes well enough, the fault is more likely to lie with the Technics. But you do not say what happens when you record and play tapes on the Technics, or when you record tapes on the Technics and play them on the JVC. Analysis of those results might point more surely at the source of the problem.

Going Into Reverse

Q. In my auto-reverse tape deck, when the tape changes direction only the drive motor reverses; the head stays stationary. Why isn't this design used in all auto-reverse decks? Wouldn't this overcome the problem of azimuth alignment in decks that use a swivel-head design? Surely it must be cheaper, as it doesn't require an extra motor to turn the head.

-Daniel Cohen, Verona, N.J.

A. One of the problems in designing and constructing a high-quality tape head is to keep the gaps co-linear, that is, in exactly the same vertical line so that azimuth is the same for both gaps.

The problem is compounded by the fact that physical co-linearity does not assure magnetic co-linearity. In the case of a reversible cassette deck which does not use a swivel head, the head must have four gaps, two for each direction of tape travel. To keep all gaps co-linear is a good deal more difficult for a head with four gaps than for a head with two. Hence a number of manufacturers have elected to go the route of swivel heads. Swivel-head decks usually have separate azimuth adjustments for each direction of tape travel.

VCR Dropouts

Q. I am considering the purchase of a hi-fi VCR solely for audio recording, because five or six hours of audio can be recorded on a single tape with sound quality superior to that of most open-reel or cassette decks. If I record only at the slower LP and EP speeds, will audible dropouts be more prevalent than at normal speed, as some audio experts contend?

-Frederick Goldsby, Pitman, N.H.

A. In theory, these experts are correct. That is, the slower the VCR speed, the more noticeable the drop-outs will be. However, much depends on the quality of the tape employed. A good tape will have fewer and briefer dead spots. Hence you have a good chance of obtaining satisfactory results at the slower VCR speeds.

Dubbing: Three to Two Or Two to Three?

Q. My stereo system includes a three-head cassette deck with a rated frequency response of 20 Hz to 24 kHz and a 75-dB signal-to-noise ratio. I am planning to buy a two-head deck for dubbing; its specs are 20 Hz to 20 kHz frequency response and 74-dB signal to-noise ratio. My problem is that I have been told by an audio salesman that it is much better to dub from one three-head deck to another three-head deck. Please advise.

-John DeRosa, Mattapan, Mass.

A. The two-head deck you plan to buy should serve quite adequately for dubbing. Apart from not being able to monitor the tape as you record, the chief drawback of a two-head deck as compared with a three-head deck is less extended treble response in play back. This drawback can be inconsequential, particularly with a two-head deck that maintains playback response substantially to 20 kHz. After all, does your program material go out to 20 kHz or beyond? Does your hearing extend that far? It is usually best to play a tape on the same deck that was used to record it.

Therefore, in dubbing, you would play the original tape on the three-head deck (assuming that's the deck it was made on) and record the copy on the two-head deck.

(Editor's Note: Playing a tape on the same deck that recorded it has two advantages. First, if the recording deck's tape speed was too fast or slow, playing it back at the same speed would cancel the effects of this error, since pitch and tempo change only when a tape is recorded at one speed and played back at another. Second, if the playback and record head were aligned at the same factory, as is the case with three-head decks, the odds of azimuth mismatches would be reduced. If the same head is used for both functions, as is the case with two-head decks, it entirely eliminates the possibility of such mismatches. However, this presumes that the re cording deck's speed and playback azimuth have not changed since the recording was made, and that you're not dubbing tapes made on some other recorder altogether. If these presumptions are not true, you'd do best to experiment to see which dubbing arrangement-three-head to two-head or vice versa-gives you the best results. -I.B.)

Tape Type and Print–Through

Q. Are Type II cassettes less susceptible to print-through than Type I tapes?

-Victor G. Alter, Amherst, N.Y.

A. High-coercivity tapes-that is, tapes with high resistance to demagnetization-are less subject to print-through than low-coercivity tapes. Inasmuch as Type II has higher coercivity than Type I, Type II is less subject to this phenomenon.

Protecting Magnetic Recordings

In the January 1986 issue, reader K. P. Moylan told of his problem with tapes going through U.S. Customs; they were being damaged by inspection devices. Mr. John Carr, of John Carr & Associates, Flossmoor, Ill., writes of his experience:

"I frequently use the U.S. mails and various carriers, namely U.P.S., Federal Express, and Express Mail, to ship magnetic computer disks. We have experienced almost 100% failure rates (unreadable data) after shipment through Customs. In the past two years, we have experienced an in creasing error rate in disks shipped via U.S. mail, even when the shipping car tons are clearly marked with colored warning stickers. We've had no problems yet with U.P.S. or Federal Express. We avoid problems by: (1) Shipping in stiff cardboard cartons secured with plastic tape and marked with colored warning stickers; (2) wrapping the disk in a single layer of aluminum foil (lead-lined photographic film pouches offer greater protection, but at higher cost); (3) cushioning the disk with air-cell material-there are special plastic packing materials for cushioning and radiation protection, available from electronics-supply houses; and (4) avoiding those carriers which have a record of damaged disks." Steven Pecsek of Riverbank, Cal., writes: "Regarding the effects of Postal Service X-ray machines on recorded tapes, I recall reading that although X-rays have no effect on magnetic tape, the large electromagnets in the machines can erase some of the signal [with the high frequencies being most vulnerable. -H.B.]. I have operated an open-reel mail-order tape service for the past 10 years and shipped perhaps 100 tapes overseas, but have never had any complaints of damage due to X-ray machines or any other causes. However, I do write on the boxes, "Do Not X-ray-Magnetic Tape." Mr. Pecsek has brought to my attention a 3M Sound Talk bulletin on the subject, dated Volume III, No. 1, 1970.

Following are some excerpts: "Laboratory-conducted tests have determined what would constitute adequate protection from stray magnetic fields of a magnitude which may possibly be en countered in transit. It was found that field strengths within the tape of 50 oersteds or less caused no discernible erasure ... . Sources of magnetic energy to which tape being shipped might be subjected would be motors, generators, transformers, etc. These devices are designed to contain their magnetic fields to accomplish some kind of work. With this in mind, it is safe to assume that field strengths of more than 1,500 oersteds would not be en countered in ordinary shipping situations.

"Because field intensity decreases rapidly with distance from the source, the 50-oersted point ... is reached at a distance of 2.7 inches from a 1,500-oersted source. From this it can be seen that the easiest and least costly method of obtaining erasure protection is by insuring a degree of physical spacing from the magnetic source. It is suggested that tape being prepared for shipment be packed with bulk spacing material such as wood or cardboard between the tape boxes and the outer shipping container.

"Three inches of bulk spacing should give adequate protection and virtually eliminate any potential for era sure. This magnetically protective spacing can also be justified because of the excellent protection gained against physical damage to the contents."

(Audio magazine, Jun. 1986, HERMAN BURSTEIN)

= = = =