TAPE GUIDE (Dec. 1990)

Dolby Mistracking

Q. I recently sent my cassette deck to the manufacturer's service department because it lacked bass and treble. When it was returned, I was de lighted with the clarity of my new recordings. But as it turns out, the tapes are brighter than the source. The problem is more evident with Dolby NR on than off. The increase in treble also produces an increase in noise. The problem occurs with all tape types.

What could be wrong? Do you believe this will be an expensive thing to repair?

-Scott Hauk, Holland, Pa.

A. It seems that something has gone wrong with the Dolby circuitry and that you are entitled to have the problem corrected free of charge either by the manufacturer or by an authorized service shop in your area. It may be worth the expense of a long distance telephone call to contact the service center and ask what procedure to follow.

My guess is that the Dolby circuit is barely working, if at all, in playback.

When you encode with Dolby in re cording, you are boosting the treble. In playback, Dolby is supposed to pro vide complementary treble cut. But your deck apparently is failing to do this properly.

If you pay for the repair yourself, I have no idea what the cost would be.

But it could be quite high, as the mini mum charge these days is often $50 or more.

Reading About Audio

Q. I have the opposite problem from the reader who complained, awhile back, that some of the "Tape Guide" questions were too unsophisticated for him; I find Audio too advanced for me.

I need a book for beginners that ex plains the terminology used. One has to start someplace, and if one doesn't have prior experience, Audio is all Greek, especially the equipment pro files. Could you please recommend a few books that might be helpful to a novice like me?

-Rick Frank-Jones, O'Fallon, Mo.

A. Rather than recommend specific titles, I would like to make some general suggestions. Visit audio dealers in your area to see what books they have.

Glance through them to see if any are your cup of tea. Write to Tab Books, Blue Ridge Summit, Pa. to find out what they currently have available. Tab has published a number of books on audio for beginners, but they go out of print from time to time. You can also write to the Audio Engineering Society, 60 East 42nd St., New York, N.Y. 10165 and inquire what they have. Two other good sources are Mix Magazine's Bookshelf, 6400 Hollis St., #12, Emeryville, Cal. 94608, and Sams, 11711 North College Ave., Carmel, Ind. 46032.

Check your local library. Comb back issues of periodicals such as Audio, Stereo Review, and High Fidelity, which from time to time have contained explanatory material. And keep reading Audio (and other periodicals) even though the material is initially over your head. Gradually, it will start to make sense. If an article appears to contain important information, read it several times. We publish book reviews, less frequently than we'd like, so watch for The Bookshelf column. Our current favorite for the type of knowledge you desire is Glenn D. White's "The Audio Dictionary" from the University of Washington Press.

Silent Spots

Q. Every so often, when I play back a cassette tape, the sound will abruptly stop for a second and then resume, as if the tape head were losing contact briefly. This happens only once in a while, but it is extremely bothersome to me.

-David Abbou, Alexandria, Va.

A. The problem could be in the tape, the head, or the electronics. If the silence always occurs at the same places in the recording, the tape is at fault. Causes could include improper coating of the oxide or embedded dirt.

If the silence occurs randomly, the fault could be in the tape head. If your deck has separate record and playback heads, there may be an intermittent connection to or within either head. If the problem disappears when the tape is played on another deck, the trouble may be in your playback head. How ever, the problem could be in either the record or playback electronics again perhaps owing to an intermittent connection. It could also be that a high signal level, either in recording or play back, is overloading the electronics and causing them to "block" momentarily, resulting in a brief silence until the electronics recover.

This kind of problem requires systematic signal tracing, and you may well need the help of an expert technician. Inasmuch as your problem occurs only once in a while, it becomes hard to track down, so that repair would be expensive. The best course may be to live with it until the trouble becomes more frequent and thus easier to spot.

Which Tape?

Q. I recently bought a mono AM-FM radio with non-Dolby cassette recorder. Please tell me the better brands and types of tape, mostly for voice.

- Oscar Weinberger, New York, N.Y.

A. For your purpose, a low-price, name-brand ferric-oxide (Type I) tape should be adequate. The policy of this magazine prohibits me from recommending specific brands. Leading brands and their prices are listed each year in the October Audio, and from time to time the magazine runs large scale comparative test reports of tapes. (The last such test was in the March, 1990 issue.) Check with your audio dealer as to which brands he carries and sells the most of. Avoid unbranded tapes, even though their prices may be attractive; they are more likely to cause difficulties.

De-confusing Playback Equalization

Q. I am 18 years old and have acquired a general knowledge of audio products and their functions. But one thing puzzles me about recording with chrome tapes. One day I noticed that if I recorded such a tape with the deck in Chrome position and later played it back in the Normal position, the sound was more brilliant than if I played it back in the Chrome position. Is this the way it's supposed to be done? I further noticed that if I recorded and played a chrome tape with the deck in Normal position both in recording and play back, the sound lacked that brilliant punch that led me to use chrome tapes in the first place. I hope that you can clear all this up for me.

-Charles Eisenhardt, Whitestone, N.Y.

A. Recording and playback equalization are designed to work together so that they will, when the tape's own response is taken into account, yield a record-playback response that is essentially flat. Playback equalization consists of a defined pass boost (which can also be considered as a treble cut); recording equalization is a slight treble boost.

The equalization originally developed for what is now called Type I tape uses less bass boost in playback and less treble boost in recording than Type II equalization. As a result, recordings made and played back with Type I equalization are less prone to saturation (i.e., have more headroom), but have a few dB less S/N than recordings made and played back with Type II EQ-regardless of the actual tape type used.

When you make a recording with Type II (Chrome) EQ and play it back with Type I ( Normal) EQ, you are applying less of a treble drop than is required for flat response. This is equivalent to a treble boost that amounts to about 4.5 dB by the time you get out to 10 kHz or above. There fore, the playback will sound bright. At the same time, you are getting slightly less S/N than if you used Type II equalization throughout. If, on the other hand, you were to play a Type I recording with Type II playback equalization, you would get less treble, and a duller sound, than if you had used matching EQ in playback and recording, but you'd also gain a few dB of S/N.

If your deck's record equalization and bias are both selected by the same switch, however, it is important that you at least record at the switch setting that corresponds to the tape type in use, to ensure proper bias. Re cording Type II tape with Type I bias would result in exaggerated treble and increased distortion; recording Type I tape with Type II bias would result in noticeably diminished treble.

What Happens If ...

Q. When taping an LP in stereo, if the channel levels on the LP are un equal but I make them equal in recording, what happens to my tape recording? Does it become for all intents and purposes a mono tape, or will there still be stereo separation?

-Joe Wilson, Pasadena, Cal.

A. Equality or inequality of recorded levels has no effect on stereo separation, although of course it can affect imaging. Adjustment of the balance control of your audio system in play back can restore proper imaging. This assumes that you are experiencing a constant, overall imbalance; momentary imbalances toward one channel or the other are normal in stereo recordings, as not all musicians in a group play equally loud at any given moment.

(Source: Audio magazine, Dec. 1990, HERMAN BURSTEIN)

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