TAPE GUIDE (Aug. 1983)

Reducing Disc Noise

Q. If I want all the sound available on a disc, must I accept any noise the disc might have?

-August Yirsa, Brookfield, Ill.

A. If you want to reduce noise al ready present on a disc, your recourse would be to what is called a single-ended noise-reduction device, such as the Burwen or DNR. It works essentially on the principle of reducing high-frequency response when there is little high-frequency content in the program material; this cut in treble response simultaneously reduces the apparent noise. When there is appreciable high-frequency content, full treble response is restored, but then the program material masks the noise.

Bias Change in dB

Q. My cassette deck has a manual bias adjustment with five settings above and five settings below "nor mal" for a given type of tape. Do you have an idea of the bias range covered by these positions, and of how I can relate them to the bias adjustment required by given brands of tape of a particular type?

-Name withheld

A. For a given type of tape, most brands fall within about 80% to 120% of "normal" bias. My guess is that each setting of your control produces about a 6% (0.5 dB) change in bias.

Accordingly, the minimum and maximum settings of your bias control would respectively produce bias 2.5 dB below and 2.5 dB above the normal setting. This translates into 75% and 133% of normal bias, which is consistent with the 80% to 120% range referred to above.

Setting Record Level

Q. I would like to know at what signal level to record, as indicated by the meters of my cassette deck.

-Jimmy Hunter, Fort Myers, Fla.

A. Generally speaking, record-level indicators are calibrated so that whether the indicator is average-reading or peak-reading, one obtains best results (high signal-to-noise ratio without excessive distortion) by advancing re cord level to the point where the indicator about reaches 0 dB but seldom goes above it. In calibrating the indicator, the manufacturer usually takes into account the characteristics of typical, good-quality tapes. For a peak-reading indicator, 0 dB tends to correspond to about 3% harmonic distortion on the tape. For an average-reading indicator, 0 dB corresponds to a recording level several dB lower, perhaps 6 to 8 dB lower; this provides a safety margin to allow for the fact that an average-reading device lags behind sharp transient signals.

However, tapes do not all have the same characteristics. Some allow a higher recording level than others be fore 3% distortion is reached. Then one can let recording level exceed 0 dB, typically by something like 2 to 5 dB.

One may have to experiment a bit to find how high recording level can be set without encountering noticeable distortion. Further, one may find that maximum satisfactory recording level varies with program material.

"What Should I Buy?"

Q. I am considering the purchase of brand X, brand Y, or brand Z tape deck. Please help me decide which one is best for my needs.

-John Q. Public, Main St., U.S.A.

Q. I have about $600 to spend on a tape deck. Please advise me which one is the best for the money.

-Jane Q. Public, Elm St., U.S.A

A. If is again necessary for me to issue my periodic reminder that the policy of Audio prohibits the "Tape Guide" column from recommending specific brands and models of audio equipment (except in unusual cases where there is only one of a kind on the market).

The first step in deciding what to buy is to become knowledgeable about the subject matter. One way to do so is by reading the tape deck reviews that appear in Audio and other periodicals.

Consult the tape deck directory that appears annually in Audio's October issue to become familiar with the comparative features and specifications of the decks you are considering. Check with your audio store or library for a readable book on the subject of tape recording. LISTEN to the decks you are considering. Using a phono disc of good quality, notice how faithful a copy each of the tape decks can make and how faithfully they can reproduce inter-station FM noise. See what parts and service warranties come with the decks; find out how far it is to the nearest authorized service agency. Try to find out which tape decks come in least frequently for service relative to the number sold.

Armed with all this information, determine your priorities regarding specifications and special features. Consider the amount of money you can afford to spend and also where to spend it i.e. , look around for a store whose reputation you can trust and whose personnel seem both knowledgeable and helpful. Then decide which brand and model offers you the most value.

Updating Heads

Q. Would it be possible to replace the heads on my TEAC 6010 with high-density ferrite heads? I have been told by a technician that the impedance of the new heads is different.

- Chandler Ellis, APO San Francisco

A. This type of question is best answered by the manufacturer. He can tell you what replacement heads are suitable for his particular machine and what changes may be required in bias current, audio drive current, equalization, and record-level indication. An other source for such information is Nortronics, which makes replacement heads for a wide variety of tape machines. (You may wish to write Nortronics at 8101 Tenth Ave. North, Minneapolis, Minn. 55427.)

How Many Dubs?

Q. I sometimes wish to dub. How often should I be able to dub a cassette tape before a substantial quality loss is noticed?

-J. Bill Such, Natrona Heights, Pa.

A. I do not know whether you refer to multiple dubbings from a master tape or to sequential dubbings from one tape to the next. In the case of multiple dubbings, if your master re cording is on good tape you probably should be able to run the master tape several hundred times, perhaps 500 or more.

If you are making sequential dubbings-dubs of dubs-you probably can't go beyond the second or third generation without noticeable increase in noise and, quite possibly, alteration of frequency response. Each dubbing introduces about 3 dB more noise.

Thus, the third generation (not counting the master tape) has about 9 dB more noise than the master tape. If you start with a fine deck having signal-to noise ratio of something like 70 dB (with noise reduction), the third generation dubbing has S/N of about 61 dB, which is still apt to be satisfactory. But if you start with something like 60 dB, S/N of only 51 dB is unlikely to be satisfactory.

The "Ultimate" NR?

Q. I have been shopping for a cassette deck and find some that offer dbx noise reduction. If this is the ultimate in noise reduction, why are so many other decks using NR systems such as Dolby B, C, HX, etc?

-Peter Ripley, Sebastopol, Cal.

A. Every noise-reduction system has some deleterious side effects, such as pumping (volume changes), breathing (bursts of hiss), and alteration of frequency response. They may vary with the program material and they may be audible to some persons and not to others. There tends to be a trade-off between amount of NR and amount of side effects. How far a deck manufacturer goes in NR depends on his judgment of the extent to which most consumers can accept the side effects. Hence, Dolby B NR provides less reduction than does dbx. I have heard some persons claim that they can hear dbx's side effects, while I have heard others claim that it works to their complete satisfaction. You have to decide for yourself, based on what you hear, as to which NR system to buy. Also keep in mind that if NR is not to introduce appreciable deviations from flat response, it is important that frequency response of the deck be very flat prior to NR.

Varying Base Response

Q. Why do I get more bass response with my cassette deck when recording from FM than from phono?

-Kurt Schwab, Federal Way, Wash.

A. I see no reason why a cassette deck should provide better bass response for one signal source than for another. The reason appears to lie in the signal sources. The phono cartridge you are using may be deficient in bass and/or the phono preamp section of your amp may be deficient.

Head-Cleaning Tapes

Q. What is your opinion of head-cleaning tapes?

-J. Bill Such, Natrona Heights, Pa.

A. I prefer to remain neutral on this; I cannot guarantee that they will do no harm, nor can I say that any of them will do harm. My inclination is to use a cotton swab with isopropyl alcohol or one of the special head-cleaning solutions available in audio shops.

Line/Line Mixing

Q. I want to mix two line inputs down to one input. My cassette deck has microphone/line mixing. Can you suggest steps I can take to feed a high level signal into the mike input so that I can use the mixing facilities of the deck?

-Robert Martindale, Rich, Va.

A. The problem in using the micro phone input is that of overloading the recording amplifier of your tape deck.

Therefore, you have to greatly reduce the level of the signal being fed into the mike input. Possibly this can be done via a volume control in the component whose signal is fed to the mike input.

[Editor's Note: Resistor cables, de signed to solve just this problem, are widely sold for use with portable recorders lacking line inputs.-I.B.] Another possibility is to combine the two input signals via a Y-adaptor, and feed the combined signal to the high level input of your deck. You won't, however, be able to vary each one's level in the mix unless your two sources each have level controls.

Worst come to worst, you could always buy an inexpensive, passive mixer.

Is Open-Reel Obsolete?

Q. I have accumulated a large number of recorded open-reel tapes. Do you foresee open-reel becoming obsolete 10 years or so down the road, giving way to cassette?

-Robert Ehrentraut, Burton, Mich.

A. It seems unlikely that open-reel analog tape decks will become obsolete in as little as 10 years. While the state of the cassette-deck art, including developments in tape, enables a "super deck" to rival the performance of a quality open-reel deck, it costs a great deal of money to achieve this, sometimes well over a thousand dollars. The open-reel format has several advantages over the cassette format, such as greater ease of editing, longer recording time per reel side, more headroom (protection against tape saturation at high frequencies) because of higher speed, choice of speeds, etc.

Still, the cassette deck has made substantial inroads into the market position once enjoyed by the open-reel deck. While such inroads may well continue, they don't necessarily augur complete displacement of open-reel machines.

On the other hand, recognizing the marvelous progress of the electronics art, it is not beyond belief that both cassette and open reel may eventually be displaced as home recording de vices. Considering that we live in an age where the equivalent of hundreds of thousands of transistors, capacitors, resistors, etc may be packed within an area about the size o; one's thumbnail or less, we may eventually arrive at solid-state devices of moderate size and with no moving parts that are capable of recording and playback in digital form. But within 10 years? I really can't say.

(Source: Audio magazine, Aug. 1983, HERMAN BURSTEIN)

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