TAPE GUIDE (July 1987)

NR Transfer

Q. f use a high-speed cassette duplicator which has no noise-reduction circuitry. It seems to me that this is the same as copying a tape from deck to deck with noise reduction turned off on both decks. The manufacturer of the duplicator says that Dolby B NR will be transferred to copies if the master tape is encoded with it. I suspect this is wrong. What do you say? Also, if Dolby B NR indeed transfers from master tapes, what about Dolby C and dbx NR?

-Chris Pillar, Anchorage, Alaska

A. The manufacturer of your duplicator is correct. Whatever NR encoding is present on the master tape whether Dolby B or Dolby C or dbx will be transferred to the copy.

In the case of Dolby NR, however, the transfer will be correct only if the playback and recording levels are so matched that the copy will have exactly the same magnetic strength (flux density) as the original. Otherwise.

Dolby NR systems reading the copy will not "track" properly, causing frequency response to suffer, particularly at the treble end.

Matching the level indications on your duplicator's meters (if it has separate meters for the original and the copy) may not be accurate enough. It is best to copy a tape containing a continuous test tone, then substitute the copy for the original and make sure that its playback levels read the same as the original tape's when read on the same meter. You may have to repeat this calibration for each tape formulation (brand and type) onto which you make a copy.

Mass Market or High End?

Q. I have a problem that I'm sure a lot of others share. I have about $350 to spend on a new cassette deck, and it seems that I must choose between mass-produced decks and those at the bottom of the "high end." Is there a rule of thumb when dealing with a situation like this? Both types of products look good for the money.

-Jim Sarro, Harrison, N.J.

A. My vote tends to be for the bottom of the high-end range. For the same price, such a deck will probably not have as many features and frills as middle-of-the-road equipment, but there is the factor of reliability to take into consideration. A high-end manufacturer is apt to build the same quality, and therefore reliability, into his lower priced components as into his pricier ones, and is likely to meet the com petition's price by omitting the less essential features. By reliability I mean good, consistent, trouble-free performance even after heavy use.

In answering a question such as yours, we deal with probabilities rather than certainties, and with averages rather than individual cases. It could well be that you might find a middle-of the-road deck that gives you both plenty of features and high reliability.

Tape-Type Differences

Q. Frankly, I cannot always trust my ears in choosing among tape types, and specs often confuse me. I would appreciate your views on the relative merits of the various tape types avail able.

-Name withheld

A. From the viewpoint of signal-to noise ratio and distortion, there appear not to be important differences among the three available tape types: Ferric oxide, chrome and chrome equivalents (ferricobalts), and metal particle (Types I, II, and IV, respectively).

The more important thing, with respect to noise and distortion, is the quality of the particular brand one chooses. One type of tape or one particular brand may sound better than others with a given deck because the deck's bias, equalization, and sensitivity are adjusted to best match that tape. More and more decks have automatic tape-matching systems which adjust these parameters--or bias, at least--to match just about any given tape. Of course, any deck's bias can be adjusted-sometimes by the user, or else by a technician-to match any given tape. Bias below optimum accentuates the treble, brightening the sound (though at some risk of distortion); bias above optimum enhances the rest of the range but reduces treble, giving a more full-bodied sound.

The chief advantage of metal-particle tape appears to be with respect to headroom-that is, in its ability to guard against saturation of the tape at high frequencies. Saturation is most likely to occur when the signal source contains high frequencies of substantial magnitude. Accordingly, metal-particle tape tends to provide better high frequency response than the other types when recording at high levels.

With the other tape types, one can avoid or reduce tape saturation and consequent treble loss by lowering the recording level by several dB, but this means a reduction in signal-to-noise ratio.

Under the right circumstances, your ears might be more trustworthy than you think. Try recording the same demanding passages of music on sever al different brands and varieties of tape, and see what differences you hear in playback. Also, try recording the noise heard between stations on an FM tuner (you'll need to turn off the tuner's muting switch, if it has one) at an indicated level of- 20 dB. Differences among cassettes in frequency response and dropouts are often easier to hear with interstation noise' than with music.

"Line In" for Mikes

Q. Long ago, cassette decks had microphone jacks for live recording.

Most of the new models do not have this feature, it seems. I assume that one can plug microphones into the "line in" jacks at the rear by using suitable plug adaptors. Will this yield satisfactory recordings? Does one need an equalizer and/or preamplifier? If a preamp is needed, what about a small mixer, which I have?

-John Durand, East Haddam, Conn.

A. If the microphones you plan to use are of the garden-variety ceramic kind, usually costing but a few dollars each, you can feed them into the line inputs of your cassette deck (via suit able adaptors) and obtain more or less satisfactory results. In terms of frequency response and distortion, the results will not be high-fidelity, but they may still be quite acceptable for speech. One of the problems you may face in terms of frequency response is loss of bass because of insufficient load resistance; this may be a blessing for recording speech but quite other wise for music.

If the microphones are of a good grade, usually a dynamic (magnetic) type, there probably will be insufficient gain at the line input to enable you to achieve an adequate recording level.

Then you will need a preamplifier, or perhaps a mixer will be able to provide the required gain. (If your mixer does not, you might try one of the inexpensive models on the market.) Equalization is not needed.

(Editor's Note: The presence of microphone inputs is addressed in the "Cassette Deck" section of our Annual Equipment Directory. In the October 1986 issue, approximately 44% of the listed models have at least one micro phone input; of this group, most models have two such inputs.)

Playback Pops

Q. During playback of some of my cassettes, I hear pops at different volume levels. I thought maybe it was the heads of the deck, but I got the same results during playback of these cassettes on other, and pretty expensive, machines. Is this caused by a static buildup, and will it damage my tapes? How can I prevent this noise?

-Steve Franks, Wichita, Kans.

A. You fail to say if your offending cassettes are ones which you recorded yourself or if they are commercial, prerecorded tapes. If they are your own recordings, these pops may be due to the phono disc from which the cassette was copied-either your own disc or one played by the radio station whose program you taped.

An alternative explanation is that there are static charges on the tape.

The only solution I know of is to rap the cassette against a firm object, sharply but not so hard as to damage the cassette (or the object).

The cassettes in question will not damage your deck. However, if the pops are extremely loud and you are playing at very high volume, you might damage a speaker.

Crosstalk in a Preamp

Q. When I play a tape, with my preamp's selector switch turned to tuner or phono or AUX/CD, I can hear the tape at very low level. Why?

- Mike Radoncic, New York, N.Y.

A. Ideally, there should be complete separation among signal sources in a preamp. High-quality preamps come close to this ideal, although not all to the same degree, through careful lay out, shielding, and other tactics. In less expensive preamps, there may be greater distance between actual performance and the ideal, resulting in audible crosstalk.

It appears the designer of your preamp hasn't taken adequate care to minimize crosstalk. On the other hand, does it truly interfere with your listening to the tape deck or to other sources? If so, shutting off all program sources except the one in use will solve the problem, albeit inconveniently.

(Source: Audio magazine, July 1987, HERMAN BURSTEIN)

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