TAPE GUIDE (Feb. 1985)

Tape Hiss

Q. I have about 95 cassette recordings made from FM on an old deck. Although recorded with Dolby NR, they have considerable tape hiss. They still sound pretty darn good, except for the hiss-my main problem. Some of these tapes are priceless to me, so I am not disposed to just forget about them, as one person suggested. What is the best way to get optimum fidelity but with a reduction in tape hiss? For example, should I dub my tapes onto new tapes, perhaps metal? Would I dub with Dolby C NR on the recording deck? If you say I shouldn't dub, would I play my tapes on a new deck with Dolby B or Dolby C? Which produces less hiss?

-William R. Charmack; Miami, Fla.

A. Once noise is on the tape, there is no way to reduce it by means of dubbing. However, one can often get more or less satisfactory results by using a dynamic filtering noise-reduction unit. This is sometimes called a single ended NR system because it operates only in playback, in contrast to double ended systems, such as Dolby and dbx, which encode in recording and decode in playback. (See the October 1984 issue of Audio for a directory of NR units, both single- and double-ended, and the plans elsewhere in this issue for building both types.) If you don't mind losing some of the music's treble, you could play your tapes with Dolby C, which would provide more treble cut than Dolby B, thus reducing noise at the same time.

EE Open-Reel Deck

Q. I am considering the purchase of an open-reel tape deck and would like to know whether one equipped for EE tape is worth it. Can these particular tapes be played on a deck without EE equalization?

-Conrad Szablewski; Flushing, N.Y.

A. Yes, EE (extra efficiency) is worth it if you obtain a deck with proper equalization and bias for EE tape.

Such tape takes advantage of the technological developments that have given us greatly improved cassette tapes. EE tape makes it possible, using an open-reel deck, to obtain performance virtually as good as regular tape, but at half-speed; for example, as good at 3 3/4 ips as regular tape at 7 1/2 ips. This would be particularly true with respect to frequency response and signal-to-noise ratio. Azimuth problems, however, would not be alleviated; that is, they would be the same at a given speed (say, 3 3/4 ips) no matter whether EE or conventional tape is employed. EE tape calls for playback equalization of 35 µS at 15 ips, 50 µS at 7 1/2 ips, 90 µS at 3 3/4 ips, and 120 µS at 1 7/8 ips. The respective turnover frequencies (points at which bass boost is up 3 dB) are 4.547, 3.183, 1.768, and 1.326 kHz. Most open-reel decks will come reasonably close to these playback requirements if they don't exactly match them; that is, the effect on frequency response will not exceed about 3 dB. To illustrate, if you operate at 15 ips and have to use 50-µS instead of 35-µS playback equalization, this will result in a mild treble boost reaching a maximum of about 3 dB.

Abrasive Tape?

Q. Will using metal tapes wear out the heads faster than would ferric, chrome, or ferri-cobalt tapes?

-Gary Haymov, Forest Hills, N.Y.

A. I have come across no evidence or authoritative claims that metal-particle (Type IV) tapes are more abrasive than the other types. Perhaps the term "metal" is suggestive of greater abrasive power. However, the other tapes also have metal coatings-iron or chrome or a combination of the two--except that these coatings are in oxide Corm, that is, combined with oxygen.

In the early days of chromium dioxide tape, there were reports that it was more abrasive than ferric oxide tapes.

However, these reports were disproved; in fact, if anything, the chrome tapes were somewhat less abrasive.

Now, in the case of metal-particle tapes, it seems that history is repeating itself.

Treble Deficiency

Q. I have an open-reel deck with EE tape capability and dbx noise reduction. I have been using ferric tape at slow speed with dbx on. But some of the highs seem to be lost; the recording seems compressed. When I use EE tape or increase the speed or turn off the dbx, the situation improves, but not enough. Also, when dbx is off, the tape hiss is much too noticeable. I have recorded FM interstation noise and compared the tape playback with the source; the playback FM noise seems about one-half octave lower in pitch than the original FM noise. Do you have any idea what the problem might be?

-Kevin Beauchamp; APO, N.Y.

A. It is not clear to me whether you are using ferric tape when the deck's switches are set for EE tape. Substantially more bias is employed for EE tape than for ferric tape, and, because an increase in bias reduces treble, this could be a partial cause of your problem.

If you are correctly using the normal settings for ferric tapes and the EE settings for EE tapes, it sounds as though the bias in your deck is misadjusted and is excessive for both kinds of tape. Another possible cause of your problem is azimuth misalignment of the record head with respect to the playback head. Noise-reduction systems tend to best maintain flat frequency response when response is flat with NR off; departures from flat response tend to be exaggerated by NR systems. This could explain why your problem is partly reduced with dbx off.

Still another possibility is that you are recording at excessively high levels, which would tend to reduce treble response because of tape saturation at the high end.

It seems advisable to have your deck checked out, and adjusted, by a qualified technician, preferably at an authorized service shop.

Pro vs. Amateur

Q. What is the difference between "professional" open-reel tapes and those ordinarily bought by consumers?

-A. Yirsa, Brookfield, Ill.

A. Tapes of professional quality are made to top standards in such respects as freedom from dropouts, uniformity of sensitivity throughout the reel and from reel to reel, absence of splices, accurate dimensions, lubrication, uniform frequency response, low noise, etc.

(Source: Audio magazine, Feb. 1985, HERMAN BURSTEIN)

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