TAPE GUIDE (Mar. 1984)

Tape Shedding and Dropouts

Q. I am very happy with my cassette deck, but have developed a problem of my prerecorded cassettes shedding terribly. If I play one of these cassettes, lasting about 20 to 30 minutes, the head is loaded with oxide. In some cases this affects the sound quality. I religiously clean the head, pinch roller, and capstan. Could there be something wrong with the head? Also, the prerecorded cassettes exhibit dropouts and quivers. It is as though there is a dirty spot which the signal didn't magnetize. This always happens at the same places on the tape.

-Thomas Raines; Oshkosh, Wisc.

A. If your prerecorded tapes shed excessively but virgin tapes you have bought and recorded yourself don't do so, the fault must lie in the quality of the prerecorded tapes. They are often of less than top quality and therefore more susceptible to shedding. If the dropouts and quivers you describe always occur at the same places on the tape, again the tape must be at fault; these defects could be due to pronounced oxide shedding.

Recording at Home for Car Playback

Q. My home cassette deck has both Dolby B and C NR, while my car deck has neither. Also, the car deck has no bias selector switch. What would be the best way to go about recording tapes for playback in my car? I plan to use premium-grade normal and high bias tapes, depending on the type of music being recorded.

-Bradley J. Anesi, Oswego, N.Y.

A. For car playback without Dolby NR, theoretically you should record your tapes without Dolby in order to obtain flattest frequency response. However, as a practical matter, you may find it more to your liking if you record with Dolby B. This will add some treble boost, which in the noisy environment of a moving car may be desirable. Dolby C will add even more treble emphasis, but probably too much. The absence of noise reduction in a car deck tends to be slightly less important than in the case of a home unit, because car noise (when the motor is on) tends to mask audio system noise.

The fact that the car deck has no provision for bias adjustment is completely unimportant so far as playback is concerned. Bias is employed only in recording.

You do not state whether your car deck provides for a choice between 120- and 70-µS playback equalization.

If you record with 70-µS EQ, but your car's deck provides only 120-uS equalization (as decks without an EQ switch invariably do), the result will be a moderate treble boost in playback, over and above whatever boost results from non-Dolby playback of Dolby-encoded tapes.

Half-Speed for Cassettes

Q. My cassette deck operates at half-speed (15/16 ips) as well as at normal speed. Using metal tape, I have been impressed with the results. I wonder why more companies haven't come up with half-speed decks.

-James E. Shields, Chicago, Ill.

A. To achieve high fidelity at 15/16 ips is far from easy, and cassette decks today (except for the very cheapest, selling below $100 or so) do aim at a high level of performance. The problems include maintaining high-frequency response, which requires an extremely narrow gap in the playback head and virtually perfect azimuth alignment; risk of saturation at high frequencies because of the large amount of treble boost needed in recording at 15/16 ips, and keeping wow and flutter suitably low. While these problems can be surmounted, it is costly to do so.

Hence, cassette-deck manufacturers, as things now stand, have virtually given up on half-speed. On the other hand, a revival of interest in half-speed is possible, along with an improved ability to satisfy this interest owing to constantly advancing tape technology.

Record Level Technique

Q. There have been many suggestions made to me regarding the best cassette recording technique. These range from adjusting the record level to read 0 VU during peaks in the musical program to the technique described hereafter, which is the one I use. [In essence, this consists of taping a phono disc at successively higher levels, noting the record level reading for each, and noting in playback the highest level that comes short of audible distortion. -I.B.] I have run into one problem using this technique: My tapes of certain programs are not compatible with some other decks, so that distortion is heard in playback.

-John Vitucci, Melville, N.Y.

A. The technique you have adopted is one that I have recommended, namely that, for a given type of tape, you should experimentally determine how high you can record before noticeable distortion sets in. If a tape so recorded sounds okay in playback on your deck but not on some other decks, the latter apparently are at fault. Their playback heads or playback electronics (or both) are being overloaded by the high signal levels on your tapes.

VU Meters and "VU Meters"

Q. Why do open-reel tape decks still incorporate pseudo-VU meters rather than the new peak-reading fluorescent or LED displays?

-Patrick J. Hoepfner, Portland, Ore.

A. Some open-reel decks have true VU meters, which have standard specified characteristics with respect to response and decay times, frequency response, and overload. But, as you say, others have pseudo-VU characteristics that depart from standard.

Some manufacturers, or at least their marketing personnel, apparently feel that a meter is more "professional looking" than other types of indicators, and thus lends more cachet to the deck. Inasmuch as a true VU meter tends to be relatively expensive, similar but cheaper meters have sometimes been substituted.

Dolby vs. dbx NR

Q. What are the relative advantages and disadvantages of Dolby and dbx noise-reduction systems?

-William J. Flickinger, Barberton, Ohio

A. Dolby B tends to reduce noise about 8 to 10 dB, Dolby C about 18 to 20 dB, and dbx about 30 dB. Dolby C has a special treble boost curve in recording that serves to reduce the chance of tape saturation and treble loss; this is achieved by a drop-off in treble boost at the very high end.

Dolby tends to produce less distortion than dbx at low levels, while dbx has the advantage with respect to distortion when recording high-level signals.

Dolby requires adjustment of the tape deck with respect to the particular tape being used, to match the tape's sensitivity (amount of signal output for a given signal input); input and output levels must match in order to achieve good tracking, namely preservation of treble response.

Wow!

Q. My cassette deck was purchased three years ago, and its performance has been satisfactory until recently, when I began to detect wow in playback. This is true for all cassettes, whether commercial prerecorded ones or my own recordings. It is very slight, and some acquaintances state that the deck sounds perfectly normal to them.

However, it definitely does not sound normal to me. I have thoroughly cleaned the capstan, pinch roller, and heads, but with no improvement. I would appreciate your suggestions.

-J.R. Joslin, Key Largo, Fla.

A. Sensitivity to wow varies among individuals, which could explain why you hear something that your friends do not. I doubt that the problem lies in your cassettes, although this could easily be checked by playing them on other decks, say those of your acquaintances or at an audio store. The fault probably lies in your deck. It could be such a thing as a slipping belt or an out-of-round idler wheel. If you are mechanically adept, perhaps you can get inside your deck and have a look-see, and clean or replace the offending component. But in most cases one is best off with the services of an authorized shop or the factory.

Crystal Ball

Q. Reviews of VCR machines with high-fidelity audio, such as the Sony Beta Hi-Fi, indicate audio specs which approach that of digital tape decks. Do you think that an entirely audio tape recorder which employs video techniques will ever become available? I realize that in the case of decks such as the Sony, one can use the audio portion alone without the video, but consider the number of extra tracks that would be available without the video portion.

-Carl V. Ashworth, Richmond, Va.

A. Your guess is as good as mine. I imagine that both the VCR and digital approaches to tape recording will be assiduously explored in the continuing search for high-quality recording at consumer-affordable cost. In view of the better specs obtainable with digital techniques, even though those for VCR are very good, it seems that digital will win out. With digital, frequency response is ruler flat, and distortion and noise are almost nonexistent. Further, digital enables one to dub repeatedly with ,no loss, or virtually so. On the other hand, there are some "golden ears" who claim to hear things in digital recordings that they don't like. This might influence the way things go.

Muffled Sound

Q. I have just purchased a cassette deck and am really happy with it except for one problem. When I put in a tape to play, I get a muffled sound; it seems there is no treble. So I stop the deck, start it again, and then the music sounds normal. This happens with more than one tape, but not all the time. I would appreciate help with my problem.

-Todd Gebhardt, Exton, Pa.

A. I do not have a definite answer. Perhaps, when you first insert the tape, the azimuth alignment is incorrect; that is, the gap of the play head is not at a right angle to the long dimension of the tape, and the process of stopping and restarting the transport somehow re-seats the tape and achieves correct alignment. When you insert the tape into the well, do you do so carefully and fully?

There is also the possibility that the problem lies in the electronic circuitry. There may be a poor connection in the playback circuit, which is restored when the deck is stopped and started.

I'm sorry to be so indefinite, but the solution to your kind of problem usually requires a checkup of the deck in question--ordinarily by a qualified technician.

(Editor's Note: There is also the remote possibility that there's dirt on the heads which is being shaken loose by these manipulations. If the deck is new, as appears to be the case, that's rather unlikely, though. -I.B.)

(Audio magazine, Mar. 1984, HERMAN BURSTEIN)

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