TAPE GUIDE (Jul. 1983)

Trilling Adventures

Q. When I record some vocalists, I get a trilling "st . . st . . . st" sound on the tape. It is even worse when the vocalist emphasizes a word with an "s" or a "t" in it. It sounds as though an AM radio were mis-tuned, and it is very annoying. I have tried almost every thing to correct this, such as adjusting the manual bias and azimuth, cleaning and demagnetizing the heads, and using different brands of tapes and cassettes, but with no luck. Where do you think the problem lies?

-Nang Tom, Ottawa, Ont., Canada

A. Your problem sounds like tape saturation, which would be caused by applying excessive signal level to the tape. Possibly the record-level indicator is misadjusted so that it doesn't adequately warn you of excessive re cording level. Try recording at reduced levels. Alternatively, the fault may lie in the record amplifier, which, owing to poor design or faulty components, cannot adequately handle high signal levels.

High Recording Levels

Q. The owner's manual for my cassette deck recommends a peak level of about 0 to 1 dB on the meter to minimize distortion in recording. How ever, I have a B & O demonstration cassette that registers playback peaks of +5 to +8 dB without audible distortion. Shouldn't I be able to record at similar levels? Is my manual ultra-conservative?

-James Macak, Milwaukee, Wisc.

A. First, unless a tape deck incorporates means of calibrating the meter's playback level indication for the specific tape in use, the recording and play back levels will not necessarily agree with each other. Playback level will vary with the tape's sensitivity, that is, with its signal output for a given signal input. It may well be that the demonstration cassette tape has high sensitivity. It may also have high MRL (maxi mum recording level), permitting a higher than typical signal level to be recorded on the tape without incurring excessive distortion. Further, the B & O tape was recorded with HX Pro circuitry that reduces the tendency toward tape saturation and hence distortion in the treble range. It does so by using high-frequency content of the audio signal as part of the bias signal, which permits reducing bias current and in turn reducing the amount of treble boost. Therefore, it may be possible to record at a higher than usual level without incurring noticeable distortion and treble loss.

It could well be that your manual's recommendations for recording level are conservative, affording a safety margin to accommodate tapes with lower MRL-that is, the amount of signal one can record on the tape without exceeding 3% harmonic distortion. If you are using high-quality tape, you can probably exceed the manual's recommended recording level by several dB. It is advisable to experiment.

Tape Squeal

Q. Lately, I find that after several playings, some tapes emit a squealing noise when I play them on the cassette deck in my car. This only occurs with one brand of tape, and the same tapes sound fine in my home deck. Any suggestions?

-Terry Racicot, Norman, Okla.

A. The cause of tape squeal is seldom easy to figure out. Some combinations of tape and deck-even when both are of high quality-don't work well together in a physical sense and are apt to squeal. As the tape wears, it loses some of its lubrication, increasing the chances of squeal. Yet this will occur with one deck and not with another.

A possible cure, though perhaps only temporary, is achieved by placing the tape and a well-moistened piece of blotting paper in a container for two or three days. Tape-head cleaners and lubricants may help, too. My only other suggestion is to try another brand of tape.

Dubbing Dolby

Q. Both of my cassette decks (different models, same manufacturer) have been calibrated by the factory service so that in both cases 0 VU on the meter in playback corresponds to Dolby level, namely 200 nWb/meter. I have made a calibration tape for my self, using the built-in 400-Hz tone of Deck A. This tape plays back at 0 VU on Deck A. I play this tape on Deck B, adjusting gain so as to read 0 VU. To dub a tape, I play it on Deck B and record the copy on Deck A with both Dolby circuits off. My direct comparisons with tapes using the same procedures, but with both Dolby circuits on, show that the copies are more faithful to the original when all noise-reduction circuits are off during the copying pro cess. Of course, either way yields copy tapes intended for playback with Dolby noise reduction on.

- Steve Freides, New York, N.Y.

A. If everything is properly adjusted, yours is the best dubbing procedure inasmuch as it involves the least tampering with the audio signal. In your case, you have apparently insured good tracking between the two decks, and therefore proper signal transfer, by properly calibrating the decks to each other. However, many audiophiles are not in a position similar to yours, so that they are usually best off, at least from the viewpoint of maintaining correct frequency response, playing with Dolby NR on and recording with Dolby NR on. Still, it is worth experimenting to see what results one can get with the Dolby circuits off.

End of the Model Run

Q. I have been told that when a tape-deck model is being phased out, companies sometimes use cheaper parts in the last lot produced. A sales man told me this about a specific deck, and showed me a statement on the specification sheet that the company can at any time use different parts, without advance notice. I didn't believe him, and I still don't. Would you please elaborate on this?

-Keith Andre, Cupertino, Cal.

A. In the first place, are you sure the statement on the spec sheet actually referred to parts? The usual disclaimer is that the company reserves the right to change specifications at any time, and usually refers to minor upgrades of features or performance which occur during the model run. If anything, the Vast run in the series might be superior to earlier units, since the last decks would incorporate all such changes and improvements made during the model run to improve performance or eliminate bugs.

The claim that cheaper parts are used in the last run sounds like fiction to me, too. I can't swear it never hap pens, but I see no reason why it should.

A company generally orders or makes parts in substantial numbers, so it might cost more to special-order a run of inferior parts. The potential cost saving is usually quite small, and, in fact, using inferior parts could increase the company's costs for in-warranty repairs.

Finally, a company has a good deal to lose by jeopardizing its reputation.

Low-Frequency Turnover

Q. Is the playback low-frequency turnover for cassette tapes 50 or 100 Hz? Both have been cited here.

-Martin Nagel, Chagrin Falls, Ohio

A. I apologize for the confusion. The low-frequency turnover for cassette tapes used to be 100 Hz at 1 7/8 ips. Thus, the 1969 "Standards for Magnetic Tape Records" published by RIAA gave 100 Hz; the 1977 revision gave 50 Hz.

To fill out the picture: For all speeds and for both open-reel and cassette tapes, the low-frequency turnover is 50 Hz. I might also add that the high-frequency turnover is 1,326 Hz for Type I cassette tape (ferric) and 2,274 Hz for Types II (chrome and ferricobalt), Ill (ferrichrome) and IV (metal particle).

Azimuth Alignment

Q. I own a three-head cassette deck with facilities for adjusting the azimuth of the record head. I would like to know how the record-head alignment works. Is the record head being aligned with the playback head? But if that's the case, once the record head is aligned with the playback head, why is the alignment incorrect when I put the next tape in the deck? When I purchased the deck, I failed to have the playback head alignment checked. I later discussed this with the dealer and was told that it doesn't mat ter. Yet tapes made on a deck that I previously owned are unusable on my new deck. The salesman said that head alignment has nothing to do with it and that the equalization curves of the two decks are different. He also said that the cassette industry has no standardization for the playback equalization curves. Is playback head alignment critical?

-Name withheld

A. Correct azimuth alignment, with the head gap at right angles to the recorded track, is very important if tapes recorded on one deck are to provide full treble response when played back on another. If the deck has a single record/playback head, any error caused by misalignment in recording will be compensated by equal error in playback, and treble response will be maintained-but only for tapes made on that deck. With a three-head deck, alignment errors in one head will not be compensated by errors in the other, which makes the problem easier to spot.

Alignment is corrected by adjusting tie playback head for maximum output from a high-frequency test tape with correct alignment. The record head, if separate, is then aligned to make tapes yielding maximum output at the playback head.

However, the tape guide system of a cassette may not be sufficiently precise, allowing the tape to wander a bit with respect to the tape heads. The result is that azimuth alignment may differ from one cassette to another, from one side of a cassette to the other, and possibly from one time a cassette is played to another.

In a deck such as yours, the play back head's azimuth is aligned and locked, but the record head is left adjustable to compensate for the effects of tape wandering or "skew." Using a built-in indicator or automatic system which senses playback-head output, the user can then align the record head to match the tape.

The new Nakamichi Dragon takes the opposite approach, with the record head fixed and the play head automatically adjusting itself to match the azimuth recorded on each tape.

With respect to what your audio salesman told you: It does matter whether the playback head has correct azimuth if you are to play tapes recorded on other decks. It is also possible that your former deck was out of alignment. The industry does have standard playback EQ curves, which are quite carefully followed by all cassette decks with any pretension to quality.

Impedance Mismatch

Q. I recently purchased a tape deck with microphone inputs rated at 600 ohms, whereas my microphones are rated at 500 ohms. Would it damage my deck if I used these mikes?

-Eric Zajack, Sterling Heights, Ill.

A. There is no danger to your deck, your mikes or the quality of their performance when used together.

(Source: Audio magazine, July. 1983, HERMAN BURSTEIN)

= = = =