TAPE GUIDE (May. 1983)

Going to the Well

Q. I am constantly dubbing cassettes, and have been thinking of buying one of the new, double-well cassette decks. However, I have been told that it is better to have two decks. Please advise.

-Jonathan Edwards, Boston, Mass.

A. When dubbing, the principal ad vantage of the double-well deck lies in its compactness and economy. The advantage of separate decks--if you spend enough--lies in the ability to achieve utmost quality. [And in having one working deck if the other breaks down. -I.B.] Whether you should get a double-well deck depends on the quality of dubbings you seek. It may serve your purposes quite well, and at a fair or considerable savings in cost over separate decks. The only way to know is to try. Check the quality of the dubbings you get on a double-well deck in an audio showroom. Better, if you can arrange for a short home-trial period, do so.

S/N vs. Frequency Response

Q. I am planning to buy a cassette deck but am confused about the specifications of the decks involved.

Exactly what are frequency response and signal-to-noise ratio, and how should I compare decks in these respects? For example, one deck may have better frequency response but poorer signal-to-noise ratio than another, or vice versa. My question is, which is better?

-Roy Wong, Oakland, Cal.

A. Frequency response refers to the range of audio frequencies that an audio component can reproduce. Usually, 1 kHz is taken as a reference, and the component is evaluated in terms of its ability to reproduce the various frequencies in the audio range as well as it reproduces the 1-kHz signal. Ideally, if all frequencies are fed to the component at equal amplitude, the component (unless its purpose is to deliberately alter frequency response) should reproduce them all at equal amplitude.

In practice, within the audio range there will be a slight variation. Ordinarily a component is considered excellent if all audio frequencies are reproduced within 1 dB of reproduction at 1 kHz.

As we approach the very low and the very high frequencies, a cassette deck's response tends to fall off. While some persons, particularly the young, may have exceptional hearing extending beyond 20 kHz, for most adults the upper limit of consequence is about 15 kHz or quite possibly less. The lower limit of consequence from the point of view of program material content is generally about 40 Hz, or possibly 30 Hz. If a cassette deck has quite flat (equal amplitude) response in the range of 40 Hz to 15 kHz with no more than a loss of 3 dB at these extremes, it is capable of substantially faithful response and deserving of the adjective high fidelity.

Signal-to-noise ratio (S/N) refers to the relationship between the amplitude of the audio signal (customarily measured in the region of 315 Hz now; formerly measured in the range of 333 to 1,000 Hz) and the noise produced by the tape and tape electronics. Once S/N exceeds 60 dB, noise tends to be reasonably inaudible unless the pro gram material is played at quite loud levels, and then chiefly during quiet passages. With the aid of Dolby B noise reduction, S/N can rise to about the mid-60s in terms of dB; with the aid of Dolby C noise reduction, to the mid-70s; with dbx, to something like 85 to 90 dB. There is some tendency for frequency response to be less flat when such noise-reduction devices are used, but the extent to which this happens depends on the care with which a particular deck is designed and aligned.

It is difficult for me to tell you the extent to which one should be willing to trade off frequency response for S/N.

This is a personal decision. Fortunately, today one can find many cassette decks that provide both good response and high S/N. I think your decision should be made on the basis of listening, equipment reviews, and price.

Direct Drive vs. Belt Capstans

Q. Are direct-drive capstans superior to conventional belt-drive capstans?

-Alfred Chiesa, Springfield, Mass.

A. I have no basis for preferring one drive system over the other; some direct-drive decks are superior to some belt-drive ones, and vice versa.

As in turntables, belt drives, if properly done, can damp out vibrations and minute speed variations from the mo tor. However, belt systems can also be subject to wow and flutter owing to variations in belt thickness and elasticity. Direct-drive systems are more prone to "cogging"--very brief changes in motor speed due to changes in the magnetic field turning the rotor. Newer motors are less subject to cogging, and it is partially smoothed out by the flywheel.

Price and Performance

Q. I would like to transfer records to 7 1/2 or 15 ips, quarter-track tape, and am considering a 10 1/2-inch open-reel deck. Would my best choice be a medium-priced deck coupled with a dbx noise-reduction unit or a deck in the Revox class without dbx?

-Thomas Kerchner, Allentown, Pa.

A. If signal-to-noise ratio is your chief consideration, you might do better with a medium-priced deck and dbx. But keep in mind that a high priced deck would tend to be superior with regard to such important considerations as distortion, frequency response (wide and smooth), speed ac curacy and stability, crosstalk between channels, reliability, operating features, etc. Also, tapes made with dbx noise reduction won't sound right when played back on decks without it; if others will play your tapes, this could be an important factor.

Still, today's medium-priced decks perform as well as or better than yesterday's high-priced ones. Accordingly, the only respect in which improved performance is noticeable might be signal-to-noise ratio. If so, the combi nation purchase may be your best choice.

Bias and EQ

Q. What is record equalization?

How does it relate to record bias and playback equalization?

-H. P. Kornick, Sanford, Fla.

A. Depending on tape formulation (Type I, Type II, etc.) and on tape speed, there are industry standards as to the amount of playback equalization-largely bass boost-which the deck manufacturer must provide. Bias current is usually chosen so that (in the deck manufacturer's judgment) it will achieve an optimum balance of the conflicting requirements of extended treble, low distortion, and low noise.

Record equalization then must be adjusted to achieve flat record/playback in conjunction with standard playback equalization. For a given tape and tape speed, record equalization-largely treble boost-tends to differ somewhat from one deck to another. But play back equalization remains the same (or it should). An increase in bias cur rent reduces treble response, requiring greater treble boost in recording.

Conversely, a decrease in bias current requires less record equalization.

Changes in bias do not affect playback equalization.

Mikes and Cables

Q. Is an omnidirectional, dynamic mike with a 1-kilohm impedance suited to my deck, which has a low-impedance (200 to 600 ohm) input? Also, since I want to use it for recording lectures and conferences, how should I best arrange an extension cord for the mike? Some local hi-fi stores have said to use simple, two-lead speaker wire, and some have said I should get shielded cable. I have seen braid shield and wrap shield, 20-gauge and 22-gauge, high- and low-impedance cable. What should I get? Should I minimize the number of connections, using one 25-foot cable instead of the more flexible arrangement of two cables each half that length? Is there any danger of signal loss in a run of 25 feet?

-Chris Joyner, Beallsville, Ohio

A. The impedance mismatch between the mike and your deck is probably slight enough to cause no notice able problems, but try it at home be fore you try a serious recording. However, its being omnidirectional may present problems if you're trying to re cord the voices of those on the podium while excluding the sounds of the audience, unless you could mount the microphone right on the lectern. Even there, a cardioid might well be preferable [especially one with a bass-cut switch to eliminate "boom" in close talking -1.81; it would certainly be preferable elsewhere. If the podium voices are amplified, the omnidirectional mike will tend to pick up the speakers as well as the direct sound.

Your cable should definitely be shielded. There is a more or less standard microphone cable with a braid shield, having a satisfactorily low capacitance of about 25 uF per foot. This cable is available at most audio stores and should serve your purposes well, with no noticeable signal loss for runs up to 50 feet or more.

It is usually desirable to minimize the number of connections, because each one introduces the possibility of a poor connection, which can cause noise, hum, loss of sound, etc.

(Source: Audio magazine, May 1983, HERMAN BURSTEIN)

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