TAPE GUIDE (Aug. 1989)

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Azimuth by Ear

Q. Is adjusting azimuth by ear a good practice? I set the azimuth screw on my Onkyo deck to be a bit more compatible with my Aiwa deck. Since I adjusted the azimuth, the sound is better. Perhaps the ear triumphs over instruments.

-G. H. Sauter, Jr., San Jose, Cal.

A. Azimuth adjustment by ear is acceptable, particularly if the signal has substantial treble content. Turning up the treble using a tone or equalizer control can be helpful in this respect.

Is your Onkyo a three-head deck? If it is, when you adjusted the azimuth of the play head, did you also adjust it for the record head so that both have the same azimuth alignment? Doing so will prevent treble loss when recording and playing back on this machine. If the record head is not truly separate but is mounted in the same casing as the playback head, such further azimuth adjustment would not be necessary with your deck.

Why the "Cellophane"?

Q. What is the purpose of the cellophane strip before the actual beginning of a cassette tape?

-Richard Harding; Peabody, Mass.

A. Any deviation in roundness of the hub of the tape reel will adversely affect sound reproduction. This deviation has its greatest relative effect at the beginning and end of the tape--namely, where the tape is attached to the hub. The leader--or "cellophane," as you call it--provides something of a "cushion" against this deviation; it also gives a visual indication of where you can begin recording. In some decks, the clear leader actuates an automatic stop and/or reverse mechanism.

Equalization for Types II and IV

Q. If you're using a high-quality cassette deck to record CDs on Type II or IV tape, would there be any advantage to recording and playing with 120-uS, instead of 70-uS, equalization? When I use 70-uS with these tape types, the sound is duller.

-Thomas L. Savio; Bloomington, Minn.

A. The 120-µS equalization setting is sometimes used with Type II tape, but not with Type IV, in order to achieve greater headroom. In other words, it can provide more protection against tape overload at high frequencies, with consequent distortion and treble loss.

This equalization uses less bass boost in playback than does 70-uS EQ; a response characteristic that slopes downward from low to high frequencies may also be viewed as treble drop. Therefore, we may say that 120-µS equalization yields less treble drop in playback. Correspondingly, it requires less treble boost in recording to maintain flat response. The smaller treble boost in recording with 120-µS equalization reduces the risk of tape overload. However, 120-µS equalization, compared with 70-uS EQ, results in about a 4.5-dB loss in S/N ratio in the upper frequencies. This is because the smaller treble drop of 120-µS equalization in playback reduces noise. With decks such as yours, which provide very good S/N ratios, the loss in S/N tends to be inconsequential and possibly inaudible if you play music at reasonable levels.

Theoretically, unless you record at excessively high levels, your recordings should not sound duller with 70-µS equalization than with 120-uS, assuming Type II tape is used. Type IV tape provides substantially more headroom than Types I and II, so there is no apparent incentive to employ 120-µS equalization with Type IV.

Problems of High-Speed Dubbing

Q. All other things being equal, why is a tape copy made in real time (1:1) better than a copy made, say, at a speed of 32:1?

-Charles Warwick; Anaheim, Cal.

A. The frequencies seen by the recording electronics and heads of the duplicator are multiples of the original frequencies. For example, if the duplicating ratio is 32:1, a 15-kHz signal becomes 480 kHz. It is more difficult for the electronics--and especially the record head--to handle a 480-kHz signal than a 15-kHz signal. The problem is exacerbated for the bias frequency.

Assuming that a 100-kHz bias signal is satisfactory at the real-time speed of 1 1/4 ips, at a duplicating speed of 60 ips (32:1), the required bias is 3,200 kHz (32 MHz), which is not the most manageable frequency in the world for the electronics and the record head to handle. The coil of the head presents a series inductance and a parallel capacitance, which, respectively, tend to restrict the flow of bias current through the head and to short-circuit this current. There also tend to be physical problems in handling the very thin cassette tape at speeds such as 60 ips.

HX Pro Retrofit

Q. I have read a lot about HX Pro and would like to add this feature to my cassette, 8-track, and open-reel decks. How is it available--as an outboard device, or as a unit that can be wired in internally?

-Tom Harrelson; Columbus, Ohio

A. To my knowledge, there is no inboard or outboard device for adding HX Pro to a tape deck's recording circuitry. Doing so would be quite difficult, since HX Pro must sense the amount of high-frequency content in an audio signal and then adjust the bias current from the deck's oscillator accordingly. The bias would have to be decreased when the high-frequency content goes up, and vice versa.

The reason is that the high frequencies themselves act as bias for lower frequencies, and the objective of HX Pro is to keep total bias, from the high frequencies and oscillator, constant.

Cassette Tape Life

Q. Under normal conditions of operation and storage, how long does it take for a prerecorded or home-recorded cassette to show marked deterioration in sound?

-Frank Muñiz; Carteret, N.J.

A. Information from a leading manufacturer of high-quality cassettes leads me to expect that such a cassette should operate satisfactorily for at least 500 passes through a deck of good quality under normal conditions--including those of temperature and humidity. That number could be appreciably higher, depending on the deck used. For example, in a deck where the pressure pad is lifted away from the tape or where other measures are taken to ensure firm but smooth tape passage over the heads, tape life may be extended.

(Source: Audio magazine, Aug. 1989, HERMAN BURSTEIN)

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