TAPE GUIDE (June 1987)

Cassette Life

Q. I am interested in buying prerecorded cassettes rather than their LP counterparts. Assuming they are both well cared for, which medium will pro vide more plays before sound begins to deteriorate?

-Robert Peterson, Oak land, Calif.

A. Generally, the cassette medium will provide more plays than phono discs before deterioration becomes noticeable. A good, well-cared-for cassette should be able to go through at least 500 plays satisfactorily. I am assuming that "well cared for," in the case of cassettes. includes appropriate cleaning and demagnetization of heads and the use of a deck with a well-engineered transport mechanism.

VCRs for High Fidelity

Q. What is your opinion of Hi-Fi VCRs as audio gear? Do they beat open-reel decks for sound quality, as some manufacturers claim?

-Doug Freese, Thornton, Colo.

A. My understanding is that Hi-Fi VCRs, both Beta and VHS, are capable of excellent audio recording in all basic respects--frequency response, noise, distortion, and accuracy and steadiness of motion. They tend to outperform open-reel decks.

As with anything you buy, be sure that you first listen to whatever unit you are considering. Judge with your own ears how the quality of Hi-Fi VCRs compares with open-reel decks. And compare features.

(Editor's Note: Hi-Fi VCRs do live up to their billing but are very sensitive to tape dropouts. To ensure good performance, follow your VCR maker's recommendations for head cleaning, and use fresh, high-quality tapes for your recordings. Do not use such VCR special features as stop-motion and visible search on tapes intended for Hi-Fi audio use, as these features increase tape wear and dropouts. -I.B.)

Automatic Adjustments

Q. I have been reading with great interest about cassette decks with automatic adjustment of bias and equalization before recording, and about decks having dynamic bias adjustment during recording (HX Pro).

Which system do you think would give the best results in such respects as frequency response, signal-to-noise ratio, and distortion?

-James A. Hawk, Oak Ridge, Tenn.

A. Decks with automatic recording adjustments seek to optimize bias and record equalization (treble boost).

They also optimize recording level to match the sensitivity of the tape being used so that Dolby noise reduction will work properly. Dolby NR requires proper tracking--that is, equal input levels and tape output levels--in order to maintain flat treble response. Proper adjustment of bias and record equalization serves to ensure flat response and low distortion.

The chief advantage of a deck with HX Pro is that it guards against treble losses caused by the signal's contribution to the total bias. The treble content of the audio signal is used as part of the required bias: as treble content in creases, the amount of bias current is decreased so that total bias remains constant. The reduction in oscillator bias means less bias erase and there fore less treble loss. It also means that the bias level always matches the signal's immediate requirements.

We don't have a case of either/or here. It is possible to have both automatic set-up adjustments and HX Pro, and thus the advantages of each. Let me add that automatic adjustment serves to widen one's choice of tapes, in addition to achieving good performance.

Interchanging

Dolby B and C Noise Reduction

Q. My home cassette deck has Dolby C NR. My car deck only has Dolby B NR. What can I do to get optimum sound in my car without re recording my Dolby C tapes to Dolby B?

-Eran Schreiber, Great Neck, N.Y.

A. If you use Dolby B NR to play tapes recorded with Dolby C, the result will be a moderate emphasis of the midrange and treble. This may or may not be objectionable. It might conceivably even be desirable if you find that your car's system needs midrange and treble boost. If it is objectionable, and if your car audio system includes tone controls (what self-respecting system doesn't, today?), a slight downward turn of the treble and perhaps a slight upward turn of the bass should essentially rectify matters.

Evaluating C-120s

The November "Tape Guide" invited readers' reactions on the subject of C 120 performance, and several have taken the trouble to respond.

Most of these readers feel there is fairly little sonic difference between C 120 and shorter lengths of the same tape formulation. Thomas C. Shedd of Wilmette, Ill. feels that "the sound quality of C-120s is not quite up to that of comparable C-90s." However, John M. Kaar of Menlo Park, Cal. notes only that he has found C-120s to have somewhat less headroom than shorter tapes. Surprisingly, he has not found print-through more troublesome with the longer tapes.

Robert F. Drake of Ashland, Wisc. points out that the better tape formulations are hard to find in this length. The C-120 tapes listed in Audio's 1986 Equipment Directory are all Type I formulations, with the exception of BASF's Metal IV. Mr. Drake indicates that TDK AD (a premium Type I) is available in Japan as a C-120.

As to reliability. two readers (Charles M. Romahn of Greenwood Lake, N.Y. and Edward J. Stephens of Muskegon, Mich.) have had no special problems, though Mr. Shedd says that in his experience this is only the case with the better tape brands. And Mr. Drake finds C-120s to be a bit more fragile.

Mr. Drake also feels that European decks do better with the thin C-120 tapes than those from elsewhere, per haps because this tape length is more popular on the Continent. And according to Mr. Kaar, it's vital to keep the torque of one's cassette drives as close as possible to 50 grams/cm, and certainly between 40 and 60 grams/ cm, or even C-60s may cause trouble.

Tape tangles, when they do occur, are not necessarily disastrous. Mr. Kaar adds that when the tape does "wrap around the capstan for no apparent reason," it can be "untangled, its wrinkles smoothed out, and [the tape] put back in the shell and even played in the same deck with no further trouble."

Bias "Tuning"

Q. My deck has a "bias tune" knob.

When is this to be used? What is the effect of cutting or boosting bias?

-Victor Caranante, Dix Hills, N.Y.

A. Bias current is supplied to the record head, along with the audio signal, in order to minimize distortion and maximize the amount of signal recorded on the tape. For each kind of tape, and for each brand, there is an optimum amount of bias current that achieves suitable low distortion, high recorded level, and good treble response. An increase in bias above the optimum reduces treble response, while a decrease exaggerates it.

The purpose of the "bias tune" knob is to permit the user to make a fine adjustment of bias so as to achieve flattest possible high-frequency response, as judged by ear. If you have a good ear, and if your deck has three heads (permitting simultaneous re cording and monitoring), you can ad just bias while recording and listening to musical program material that contains substantial high-frequency con tent. An even better way is to use FM interstation noise and adjust bias so that tape playback sounds as much as possible like the source.

Using FM interstation noise as a test signal is especially helpful if you have a two-head deck. You can't play a re cording made on such a deck until after you've rewound it. Therefore, comparing the source with the recording is much simpler if the source is a relatively constant signal, such as interstation noise, than if it changes constantly, as music does.

With either type of deck, simply switch between the noise as heard directly from your tuner and as heard in tape playback, and try the effects of slight increases or decreases of bias while you record. With a three-head deck, you can hear the effects of each bias change almost immediately after making it. With a two-head deck, you must go through several trials-record, rewind, play-until you find the bias setting which yields flattest response, as indicated by the closest similarity between the source and the tape play back.

Use an indicated recording level of -20 dB for these tests. Recording at zero level would give misleading results, as high-frequency response would be reduced by tape saturation.

Droop with dbx NR

Q. In the March 1986 issue of Audio, a review of the Yamaha K-1020 cassette deck noted that when using dbx noise reduction, there was a low-

frequency roll-off and that this was true not only for the Yamaha. I have an outboard dbx 224 noise-reduction unit connected to a pretty fair open-reel deck. Can I expect the same low-frequency roll-off? The reviewer said he missed the deep bass in some LPs; I can't remember any noticeable bass attenuation in my system.

-Mike Marino, Hagerstown, Md.

A. So far as I know, the low-frequency droop is characteristic of dbx NR rather than the tape deck it's used with. However, the droop is not very serious and is inaudible on most occasions, with most speakers, and to most persons. The droop is only about 3 dB at 40 Hz and something like 5 dB at 30 Hz. This is easily touched up with an equalizer or with a bass control.

There is also a treble droop with dbx NR, but this gets serious only beyond 15 kHz. Many audio sources and many adults' hearing do not extend this far.

Taping Compact Discs

Q. Using high-quality ferricobalt cassettes, can the wide dynamic range of Compact Discs be success fully taped with Dolby C and dbx NR?

-H. Lilienfeld, Umkomaas, Republic of South Africa

A. The noise floor and highest recordable signal level on CD are usually 90 dB or so, more than can usually be recorded on cassette, except perhaps with dbx NR. However, the dynamic range of the music on CD is usually no greater than 70 dB. Today's cassette decks, using good tapes, have signal to-noise ratios of 70 dB or greater with Dolby C NR, and 80 dB or greater with dbx NR. Accordingly, it would appear that full-range Compact Discs can be successfully copied by decks with Dolby C and/or dbx NR-even by decks having only Dolby B NR, if the music's dynamic range is smaller (as it often is). The only limitations would be a higher noise floor and some compression of high-frequency peaks, due to tape saturation.

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

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