by CRAIG STARK
Output
Q. My receiver's tape input is rated at a 250 mV with a 100,000 -ohm impedance, and the manual says to use a tape recorder of 250 mV or greater output. I've looked all over. Are there any?
-JAMES J. DODSON, JR.
Chino, Calif.
A. I think you're misinterpreting the tape -recorder input/output specification. Your receiver's requirements are well within the normal range-and they are compatible with all normal recorders! The specified 250 mV (which is the same as saying 0.25 volt) or higher is the output from the tape recorder, which you plug into the receiver's tape input. Almost all decks have outputs in the range of 0.5 to 1 volt (500 to 1,000 mV ). In contrast, the majority of tape decks have line -input sensitivities (the amount of signal needed to achieve a 0-VU recording level) in the vicinity of 100 to 200 mV, and I suspect that this is the rating you've been looking at.
Dropouts , What exactly causes tape "dropouts"?
Q. Can the home recordist do anything about them?
SHIRLEY BOTHELL, Princeton, N.J.
A. "dropout" is a momentary interruption of the signal being picked up from the tape. Often the low frequencies may seem unaffected, but for an instant there is a noticeable loss of high frequencies. In most home recorders dropout is experienced more frequently in the left channel than in the right, and while the primary cause is defects in the tape, badly worn heads or misaligned tape guides can aggravate the problem.
Contrary to what many people believe, most dropouts are not caused by tiny holes or "voids" in the tape's oxide coating. Rather, what is heard as a dropout is most frequently caused by a small protrusion that momentarily pushes the tape surface away from its normally intimate contact with the recorder's head gap. (The protrusion may be formed from a tiny bit of grit, dust, or an oxide clump.) Similarly, the undulating edge that results from a dull slitter when the tape is cut to width during manufacture can push the edge away from the head. Since the outer -edge tracks are used for left -channel information both in stereo cassettes and quarter-track open -reel decks, poor slitting also causes dropouts.
While tape dropouts were once a serious audio problem, modern oxides and coating technology make them serious only for the more critical video and data-processing tapes. If you find a large number of drop outs with the brand of tape you're using, I'd suggest trying another well-known brand. If the problem persists, then have a service technician check your deck.
Wearing Away the Highs
Q. With use, LP records lose high frequencies and gain surface noise. Do cassettes suffer in a similar way, not only with use but with age as well?
-PAUL MILTON, New York, N.Y.
A. Yes, but . . . . Years ago, when phono-stylus tracking forces were much higher than they are today and record wear was an obvious problem, it came to be believed that tapes were immune to the ravages of time and use. But, as Molly used to say to her husband, Fibber, "T'ain't so, McGee." Robert K. Morrison, then manager of the Ampex Standard Tape Lab (which produces calibrated alignment tapes used throughout the world), noted, in a 1967 article in the Journal of the Audio Engineering Society, that "short wavelengths [that is, high frequencies at slow tape speeds] . . . are fugitive" and that "a tape recording at slow speed (3 3/4 ips or less) which is flat today may well be lacking high frequencies after storage or a number of playings." Everyone who has used calibrated high-frequency alignment tapes professionally knows that they gradually deteriorate with age and use. One high -quality cassette -deck manufacturer I know claims that he discards calibrated tapes that have been played more than ten times, though I think this is a bit extreme. On the other hand, beyond twenty-five playings / can't trust a "calibrated alignment tape" because it is likely to read low by 2 dB or more on its highest frequency band, as compared with a fresh sample. I'm sure that the experience of other testers is similar.
Does this mean that a frequently played tape quickly starts to sound like a worn-out disc? By no means. To judge by my own experience, it may well be true that, with top-quality equipment, high frequencies on LPs and tape may deteriorate at a roughly similar rate in terms of time and use, but the noise level (surface hiss, ticks, and pops) on my discs becomes unbearable reasonably quickly, whereas I have yet to discard one of my master tapes because of a higher noise level.
Four-channel Cassettes?
Q. Why can duplicating plants simultaneously record all four tracks on a cassette tape (the "side two" tracks being recorded backwards) while no consumer product makes this option available?
LAWRENCE LITTLE New York, N.Y.
A. Actually, there are several consumer cassette decks, designed to permit recording and playback in both directions without turning the cassette over, that already incorporate the same kind of four -channel heads used by duplicators to speed up the copying process by recording all four tracks simultaneously. Assuming you could do without built-in erase facilities (by using a bulk-erased or blank tape for copying, for example), these "bidirectional" machines could be used-with a second set of record electronics--in precisely the way duplicators have been using them for years.
Legally, however, the situation is some what different, for Philips of the Nether lands, as the inventor of the cassette system, can dictate the terms under which a deck manufacturer is licensed to use the phrase "Compact Cassette." Philips has always tried to maintain the position-progress notwithstanding-that, as far as consumer applications are concerned, any cassette should be playable on any cassette deck, whether that deck be the original $29 mono "sound camera" or a $2,000 stereo high fidelity component. According to reliable reports, both Dolby-B processing and the development of CrO2 (and similar) tapes strained Philips' Doctrine of Compatibility.
Tapesponding Lives! In a previous column I answered a reader's question about the existence of tape clubs, whose members exchange correspondence via tape, lend each other tapes of old radio shows, etc., by saying that they seemed to have petered out.
I stand corrected! The oldest of them all, the Indiana Recording Club, is alive and well in Indianapolis. Readers interested in their activities should address inquiries to Bill Davies, Secretary, IRC, 1729 East 77th Street, Indianapolis, Ind. 46240.
Also see: TECHNICAL TALK: More on Stereo Imaging JULIAN D. HIRSCH
Source: Stereo Review (USA magazine)