TAPE GUIDE (Jul. 1986)

Treble Loss

Q. When I record from any source, with or without Dolby NR, it seems that my cassette deck adds a lot of bass. Is this normal? I play the cassettes in my car system, and there is hardly any treble.

-Chris Valencia, Taylor, Mich.

A. You did not indicate in your letter whether this problem is heard when you play these tapes back on the deck that made them, or whether you only hear it in your car.

If you hear this problem in both places, then we must next ask whether your home deck has separate record and playback heads. If so, it may be that the two heads are not in azimuth alignment with each other-that is, the gaps of each head may not form the same angle with respect to the tape.

(This angle should always be 90°, for compatibility between tape decks.) If only your own recordings sounded "off," the problem might be caused by misalignment of either head, or of both; if tapes made on other decks also sounded incorrect, then the problem would probably be with your playback head's alignment. However, since you hear the same problem when playing these tapes in your car, the recording head is more likely at fault. If your deck uses the same head for recording and playback, an azimuth error would show up only when tapes made on this deck were played on other decks.

Excessive bias or improper equalization in recording could also cause treble loss. These causes could apply to either three- or two-head decks.

In playback, inadequate treble could also be traced to such factors as a widened head gap, dirt (including tape oxide) on the head, or improper equalization. It is more likely, however, that the treble loss occurred in recording on the one deck than that it is due to coincidental playback problems on both tape machines.

If you hear this problem only in your car, and hear it only from tapes recorded on your home deck, then azimuth problems in your recorder are the most likely cause of your treble loss. To check this, tapes which sound good in your car should be played on your home recorder. If you hear a similar treble loss when playing these tapes at home, then you have probably pin pointed azimuth error as your problem, especially if your home deck does not have separate record and playback heads. Head alignment is a finicky job which you may want to farm out.

Tape Squeak

Q. I have four prerecorded cassettes, three from the same label, that have started to squeak during play back. The squeaking gets worse with each use. Can I eliminate the squeaking by breaking the cassette shell, re moving the tape, and putting it into a new shell?

-Victor H. Oreliana, Culver City, Cal.

A. I rather doubt that putting the tapes into new shells will remedy the problem. (But it just might, particularly if the pressure pad is the cause.) More likely the tape is responsible. Some times it helps, if only temporarily, to put the cassette in a box with well-moistened blotting paper for about three days.

Incidentally, do the tapes squeak when played on decks other than yours? If they don't, it could be that something is amiss in your deck-per haps tape tension. Or it could simply be that the particular tapes and your deck are a mismatch, something that happens from time to time even with components that are individually very good.

Long-Playing Cassettes

Q. I have heard that there are long playing cassettes on the market. If so, how good are they, and how long is their playing time? Who makes them? Do they require special players? Who makes these players?

-Tommy Langerak, Fort Collins, Colo.

A. The longest playing cassettes are C-120s, which play for 120 minutes on any standard player when operated in both directions. They are generally not recommended for high-quality re production because of such problems as greater distortion, greater print-through, and a tendency toward jamming, tangling, and other physical mal functions. Hence some tape manufacturers don't make C-120s, while others offer only a very limited selection.

On the other hand, when high-quality reproduction is not necessary, they may be very satisfactory. Several readers have informed me that they have had good success with C-120s for such purposes as recording lectures and conferences. To find out what brands and tape types are available in the C-120 length, consult the Annual Equipment Directory in the October 1985 issue of Audio.

Head Misalignment

Q. I recently had my cassette deck in a repair shop to have the heads replaced. At first it sounded great, but after a while the left channel seemed to record at a lower level than the right one. Then the deck wouldn't erase the tape. I noticed that the erase head was hitting the cassette shell and not touching the tape. I turned the erase-head adjustment screw so that the head would touch and erase the tape. But now the right channel records at a lower level than the left. Can you please tell me what the problem is?

-Andy Warren, Miami, Fla.

A. Apparently the repair shop was careless about aligning the heads or securing their adjustment once correctly aligned. A record-playback head (or separate heads) requires very careful alignment in three respects:

Height, so that the two gaps cover the correct portion of the tape; azimuth. so that the gaps are at a perfect (or nearly so) right angle to the long dimension of the tape, and tilt, so that the left and right gaps make equally good contact with the tape. To make these alignments correctly. one needs appropriate test tapes. The erase head requires similar alignment. I think that you should return your deck to the shop and insist on correct alignment and securing of the alignment.

Wrong Key

Q. My cassette deck provides only for automatic switching of bias and equalization according to type of tape, using the key wells of the cassette shells. There is no manual switching. Recently I got some Type II cassettes which were mistakenly put into Type I shells. If I use a 10-band graphic equalizer, could I adjust the signal going to the tape deck for recording so as to give fairly linear response in play back? Also, please clarify the differences between Type I and Type II tapes with respect to equalization and bias.

-Bruce D. MacGregor, Victorville. Ca .

A. Type II tape requires appreciably more bias--roughly 50% more--than does Type I. Inadequate bias produces increased distortion and exaggerated treble response. You could compensate for the exaggerated treble by judicious use of your graphic equalizer, but you would still be left with the distortion problem.

In playback, Type I tape requires 120-µS equalization, signifying bass boost beginning at 1,326 Hz (up 3 dB) and leveling out (3 dB below maxi mum) at 50 Hz. Type II (as well as Types III and IV) take 70-uS playback equalization, namely bass boost be ginning at 2,274 Hz and leveling out at 50 Hz. Thus, if you used Type I play back equalization with a tape that had been recorded with Type II equalization, you would exaggerate the treble--about 4.5 dB by the time you got out to 10 kHz and beyond. On your deck, however, this problem would not occur, because the deck would automatically select the same "wrong" equalization in playback that it used in recording. No equalization mismatch would take place.

Still, considering the uncorrectable problem of insufficient bias, I think the wisest course by far is to exchange your mis-shelled tapes for correctly shelled ones.

"White-Box" Tape In response to questions about "white-box" tapes (those not identified as to manufacturer), this magazine has taken a negative position if high fidelity is desired. Our feeling has been that while such tape may be satisfactory, one faces a buyer-beware situation.

The tape may not have been originally intended for audio purposes, and therefore may not have the appropriate magnetic characteristics. It may be in accurately slit down from wider tape; it may not have adequate lubrication, and so forth. However, at least one reader has had a very favorable experience with white-box tape.

Robert E. Blay, of Rutland, Vt., writes:

"Several months ago I purchased 40 1,800-foot reels of white-box tape. The cost was about $1.35 each. I used 36 of them for a project and didn't have a clinker in the bunch. In fact, their quality exceeded that of many so-called premium tapes I have used in the past. I have been taping on open-reel for about 18 years and up to now would never have considered using white-box tape. But henceforth I'll be using it for all but the most exacting requirements. Incidentally, the supplier was not only extremely courteous and helpful but prompt. I received my order in a week."

( Audio magazine, Jul. 1986, HERMAN BURSTEIN)

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