TAPE GUIDE (Aug. 1986)

Print-Through and dbx

Q. I have noticed print-through during quiet passages of C-90 tapes that were recorded about one year ago.

How can I reduce or eliminate this? I have been recording at a level such that the average VU readings are about -10 dB and the peaks are at 0 dB. I don't think I can record at any lower level. I use a dbx Model 224 unit, and at present there is no noticeable tape noise.

-Robert R. Maigatter, Kewaunee, Wisc.

A. There isn't too much you can do to get rid of the print-through on your recorded tapes. It may help somewhat to put such tapes through fast wind and rewind once or twice before playing them, particularly after a long period of storage. In the future, you might get better results with C-60 rather than C-90 tapes if print-through is a serious problem. The C-60 tape has a thicker base and thus provides more protection against print-through.

It may also be helpful to record at somewhat lower levels, say at least 3 dB lower. Once you have S/N of about 70 dB, you have very quiet tape reproduction. With dbx NR, you have S/N in the region of 85 to 90 dB; therefore, it's quite feasible to give away a few dB of S/N without noticeably increasing noise.

S/N Standard

Q. Does there exist a reference standard for the signal-to-noise ratio of cassette decks?

- Robert Pepin, Virginia Beach, Va.

A. There is no standard reference for the signal-to-noise ratio of cassette decks (although there is a standard way of measuring S/N).

In the old days when open-reel decks reigned supreme, there were NAB (now NARTB) standard S/N ratios for various speeds and track formats.

In the case of decks intended for home use, using the quarter-track format and operating at 7 1/2 and 3 3/4 ips, the standard S/N was 45 dB unweighted and 52 dB A-weighted. (A-weighting takes into account the relative audibility of different noise frequencies, counting bass-frequency noise far less, and high treble noise somewhat less, than in unweighted measurements.) De facto, it is pretty much accepted that the minimum S/N for high fidelity is about 55 dB, weighted. An S/N of at least 60 dB does very well for most people in most circumstances, and Dolby B noise reduction achieves this in most decks. Dolby C gets into S/N ratios of 70 dB or more, and leaves very few people unsatisfied. With dbx NR, one can get S/N of 80 dB or more, and possibly over 90 dB, which leaves no room for complaint.

NR and DNR

Q. I understand how Dolby and dbx NR work, but understand less about Dynamic Noise Reduction. A car deck I have in mind has DNR instead of Dolby NR. How will my Dolby C tapes sound on it? Or should I not use Dolby NR when recording tapes for this deck?

-John Stowers, Austin, Tex.

A. You could probably get away with using Dolby B NR on tapes made for that car deck, but I would not recommend using Dolby C. Both Dolby NR systems (and dbx NR) tailor the signal in recording, then treat it again in playback to remove both noise and the effects of the prior alteration. A tape made with Dolby B NR will usually sound a bit bright when played back without this NR system. DNR, which applies selective treble cut at times when there is little high-frequency signal energy to mask noise, may or may not lessen this brightness somewhat, depending on the program material. If it does not, you could use the treble or tone control of your car-stereo system to reduce the brightness; if your system's highs are dull, you might even find this brightness, or some of it, desirable.

A tape made with Dolby C NR, how ever, is less likely to sound pleasing when played back without Dolby C de coding circuits. The Dolby C NR affects midrange as well as treble frequencies, and boosts the treble far more than Dolby B does. If your car-stereo system had Dolby B as well as DNR, you might be able to tame Dolby C tapes into listenability by using both at the same time. However, the results would still be far less satisfactory than if your car stereo had the proper circuits for Dolby C NR.

In theory, your best choice would be to use neither Dolby NR system when making tapes for the car. In practice, however, you may find it best to record with Dolby B NR; these tapes will have less hiss when played with Dolby B decoding, as they can be on your home system (and, presumably, your next car stereo), and yet can still be made to sound satisfactory over the system you're now thinking of getting for your car.

Strange Exchange

Q. I have a Nakamichi 582-Z deck and a newer deck, a Nakamichi ZX-7. Each deck does fine in playing tapes that it has recorded, and the ZX-7 does fine in playing tapes recorded on the 582-Z. But sometimes when I use the 582-Z to play a tape recorded on the ZX-7, there are strange "plinking" noises, akin to a drop of water falling into a metal bucket. The noises seem to be associated with transient spikes, such as those produced by record scratches, but I am not certain of this.

They always occur at the same place on the tape, and they are audible only during quiet passages. On many tapes, they are not audible at all. I took some of my ZX-7 tapes to my dealer and played them on several Nakamichi decks. None of them produced the noise in question. I have tried a number of remedies, such as changing tape brands, but to no avail. I would appreciate your comments.

-James G. Williams; Goodman, Miss.

A. It seems plausible that sharp transients, such as those caused by record ticks, are distressing the 582-Z.

The ZX-7 may have better playback protection against such transients than does the 582-Z. Also, the ZX-7 may be better in recording such transients; perhaps it even generates them. This problem may be similar to the effect of phono record warp on the record electronics of some cassette decks. Although the warp frequency is inaudible, it can drive the record amplifiers of some decks into great distortion. Perhaps a low-pass filter which cuts off sharply above 20 kHz or so would be helpful. It would be placed between the tape out jacks of your audio system and the input jacks of the 582-Z.

( Audio magazine, Aug. 1986, HERMAN BURSTEIN)

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