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HERMAN BURSTEIN Audible Differences Q. I notice that there are sometimes large differences among components' specifications for signal-to-noise ratio, distortion, frequency response, and channel separation. When do these differences become audible? -Ted Cumuze, Houston, Tex. A. The answer depends in large part on the program material, the level at which one operates an audio sys tem, the listener's hearing acuity, and the extent to which he concentrates on the sound. Signal-to-noise ratios of about 75 dB can yield a very quiet background for most circumstances; higher ratios offer relatively little improvement unless one plays at very loud levels. On program material such as we ordinarily listen to, harmonic distortion has to exceed about 0.5% before we notice it, and then we notice it only rarely; some tests have indicated that, for many listeners, it has to reach about 5% before be coming readily apparent. On single tones (and how often do we listen to those?), harmonic distortion of less than 0.1% is rarely, if ever, detectable. As to frequency response, some listeners might be able to detect, on direct comparison of components, differences of smaller than ± 1 dB between 20 Hz and 20 kHz, but I think the difference could easily go to ±3 dB before becoming apparent, as long as both components have flat response be tween 50 Hz and 15 kHz. Channel separation is probably in adequate if it falls well below 30 dB, which is rarely the case except for some phono cartridges. Perhaps 20 dB or even 15 dB is the borderline. Introduction of DAT Q. I am considering updating my system with a Nakamichi Dragon cassette deck, but I wonder if I should wait for DAT (digital audio tape) decks. Will DAT be a new cassette format altogether, or will it be compatible with present decks? -James M. Borzak, Raleigh, N.C. A. At present we are told that DAT decks may arrive sometime in 1986. Two different approaches are being weighed, one employing rotary heads and the other stationary heads; as of this writing, no single-format decision has yet been reached. There may well be a period of several years before DAT decks offer prices acceptable to many of us. Judging from the past history of new electronic components (such as CD players), there will probably be desirable improvements and features worth waiting for. All in all, unless you are one of those who must be first with the newest, you will have a substantial period in which to enjoy a deck as fine as the Nakamichi Dragon. I think it will be quite a while before present analog tape decks are obsolete. Look at phono turntables, which as yet have re fused to die in the face of digital CD players. There are also some people, albeit a minority, who strongly proclaim that whatever the measurements say, analog reproduction is more pleasurable than digital. Here they are talking about analog phono discs versus CDs, but we may eventually hear the same claims about analog versus digital cassette decks. DAT will also be a new format, in compatible with present cassette decks. DAT cassettes will be smaller than analog cassettes. Tape Types Q. Your article in the June 1985 issue of Audio, "The Why’s and How’s of Cassette Equalization," didn't make clear the different types of tapes. Is open-reel tape dead? I see little in the stores. I have not seen any metal tape for open reel. Wouldn't it perform better than ferric oxide tape generally does at 3 3/4 or 7 1/2 ips? -Donald Bisbee, Columbus, Ohio A. The four types of cassette tape are ferric oxide (Type I), chromium di oxide and such equivalents as ferri-cobalt (Type II), ferrichrome (Type III, now rare), and metal particle (Type IV). For open reel, there is essentially only ferric oxide. There is also EE (extra efficiency) tape, much like Type II, for open reel, but the tape and the decks with bias for it may be hard to find. Open reel is subdued but not dead. For top-quality recording, speeds faster than 1% ips (cassette speed) are still desirable. If you look in Audio's Annual Equipment Directory, published in the October issue, you will find a fair number of open-reel decks and tapes. The advantages of metal tape over the others become less apparent as tape speed increases. Hence there is no open-reel metal tape generally available. Which Tape Format? Q. In a comparison of open reel versus Beta/VHS Hi-Fi versus PCM (digital) recording, open reel appears to have the lowest fidelity of the three, at least in the case of models in the $400 to $800 range. Beta/VHS Hi-Fi would appear to be better, and PCM best. All three formats allow extended recording time. Since my use would primarily be for background music, my choice probably depends on how long the tapes will last. I know that, on an inexpensive VCR, dropouts can be seen after a relatively few plays. In the case of PCM, the error-correcting codes should help with respect to tape 1 faults. But how about Beta/VHS Hi-Fi tapes? Will the dropouts seen in video also affect the audio, and is this degradation any more serious than the degradation of open-reel tape played the same number of times? -Douglas Atkinson, Rome, N.Y. A. Your question doesn't lend itself to a definitive answer, but some comments may help. Open-reel decks using good tape can satisfactorily play the same reel hundreds of times with out noticeable deterioration. An important factor in tape longevity is tape speed relative to the heads. This speed is much greater in VCRs than in open-reel decks, inasmuch as the VCR heads are moving rather than stationary. Hence, open-reel decks appear to have the advantage so far as longevity is concerned. Of course, longevity will depend on the speed at which you operate--15, 7 1/2, or 3 3/4 ips in the case of open reel. Very good results are possible today at 3 3/4 ips. If your interest is chiefly in background music, I doubt that you will find much, if any, audible superiority in PCM or Beta VHS Hi-Fi. In addition, dropouts can be very audible on Hi-Fi videocassettes, which have no error correction. (Audio magazine, Feb. 1986, HERMAN BURSTEIN) = = = = |