TAPE GUIDE (Jan. 1991)

Maximum Recording Time

In the June 1990 issue, reader Steve Mallon of Chicago raised the question of how to get maximum recording time on a reel of tape. He was inclined to use open reel rather than cassette. Using an 1,800-foot reel and recording four mono tracks at 3 3/4 ips, he would get over six hours on one reel and maintain good quality.

Reader William I. Whitten of Birmingham, Alabama chides me for not having pointed out an alternative: Use of a Hi-Fi VCR. At the EP (slowest) videotape speed, a T-120 tape would provide six hours of uninterrupted high-quality recording. To this I would add that a T-160 videotape would provide eight hours. And going back to open reel, recording at 1 7/8 ips on an 1,800-foot reel would yield 12.8 hours, still maintaining good quality if the deck is a good one. A 2,400-foot reel would yield 17.1 hours and a 3,600-foot reel, 25.6 hours. And so on . . . and on.

-H.B.

Use of a Bias Control

Q. According to the instruction manual for my cassette deck, which has a bias control, "10% less bias is provided when the knob is fully counterclockwise, and 10% more bias is provided when it is fully clockwise." Please explain bias and how it is affected by the control. Also, in Howard A. Roberson's review of 88 cassettes in the March 1990 issue, the bias for Sony's UX-Pro tape was listed as +1.3 dB. What setting should I use for this particular Type II tape?

-Chris Murphy, Albany, N.Y.

A. The purpose of bias current, which is employed in recording and fed to the record head along with the audio signal, is to maximize the amount of signal recorded on the tape and to minimize distortion. Unfortunately, as bias is increased to minimize distortion, the bias field tends to erase the tape (in the same manner as the erase head does), particularly in the treble range. That is, bias erasure in creases as frequency rises. Therefore, the deck manufacturer seeks to optimize bias to have not so little as to incur excessive distortion, and not so much as to incur excessive treble loss.

Optimum bias varies according to tape type: Type I requires the least amount, Type IV (metal particle) re quires the most, and Type II falls in between. Optimum bias for a given tape type also varies according to brand and formulation within brand.

The March 1990 article indicates how optimum bias varied with respect to a standard level. Apparently, the Sony UX-Pro tape required 1.3 dB more bias than standard--at least in the decks employed by the reviewer.

Your best way of optimizing bias for a given tape type, brand, and formulation is as follows: Record FM interstation noise at a level about 10 to 20 dB below 0 VU as indicated on your deck.

Through trial and error, find the bias setting which yields recordings that sound most similar to this interstation noise when played back. If yours is a three-head deck, which allows simultaneous recording and playback, it's easy to compare results at different settings against the original noise. It's not too hard to accomplish with a two-head deck, because the noise at a given point on your tuner's dial will stay fairly constant, not changing from moment to moment as radio programs do.

If you use noise reduction, you should theoretically follow this procedure with NR off; in practice, you may well find it best to follow this procedure with NR on. If you don't have an FM tuner, you will have to adjust bias on the basis of a CD or LP that contains a substantial amount of high frequencies.

A Peak at Levels

Q. My deck has peak-reading meters. At approximately what levels should the peaks read when I am recording? When setting the record level, should I aim for equal readings on the left and right meters? If so, should I aim for equal peaks or equal average levels? Also, when I move the record-level knobs to the same physical positions, the meter for the left channel consistently reads higher than the right-channel meter.

-Stuart Munro; Brighton, Mass.

A. With peak-reading meters, one should ordinarily set recording level so that the peaks hit 0 dB or a few dB above; consult your instruction manual on this. Also, experiment with successively higher recording levels until you find the point where distortion or treble loss becomes evident, then back down about 1 to 3 dB.

Assuming that the meters are properly calibrated, so that equal readings produce equal levels on the tape, one should set the controls so that the two channels produce the same reading on average. If equal physical settings of these controls always produce a higher reading for the left channel, either one or both of the meters or the knobs is mis-calibrated. However, if the difference is slight, you should not find it difficult to compensate by adjusting the knobs and live with the situation until something more serious forces you to the repair shop.

A Missed Point

From time to time, I have made comparisons between Type I and Type II tapes. In the main, these comparisons have favored Type II, although not al ways. Donald Bisbee of Columbus, Ohio writes:

You miss one very important point. Type II tapes need a bass boost in order to perform as well as Type I cassettes. Such boost is rarely, if ever, provided by the Type II setting of a cassette deck, so that there can be a loss of over 6 d8 at 50 Hz. While Type II tapes at one time did have superior high-frequency response, ferric tapes (Type I) can now equal or surpass them in current formulations. This, combined with superior bass and lower price, make ferrics my usual preference. I think that ferrics sound significantly better.

I consulted on this matter with Howard Roberson, who every few years reviews a batch of tapes for Audio (the latest being a review of 88 tapes in the March 1990 issue). He stated that, yes, he has found some Type II tapes with appreciable bass compression, so that bass boost is required in playback for flat response. However, he has also found the same problems in some Type I tapes.

I find that Type I tapes have been getting better and better and often do outperform Type II tapes in important respects. As always, one's ears should be one's guide.

-H.B.

(Source: Audio magazine, Jan. 1991, HERMAN BURSTEIN)

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