Tape Guide (Q and A) (Feb. 1973)

Low-noise tape

Q. My tape recorder is adjusted for Scotch 203 (low-noise) tape. However, if I were to use a good brand of tape that isn't low noise, would this cause loss of quality? If I were to also use a Dolby unit, would this transcend the loss due to use of other than low-noise tape?

-(Michael W. Bryan, Havelock, North Carolina)

A. A tape machine adjusted for low noise tape has the following differences compared with a machine adjusted for conventional tape: (1) slightly more bias current; (2) slightly more signal drive current; (3) slightly less treble boost. Hence if you employ conventional tape with a machine set for low-noise tape, you tend to have a drop in treble response; and somewhat excessive recording level (resulting in increased distortion), which is partly offset by the extra bias. Use of a Dolby unit would not overcome these results. The Dolby, however, would reduce noise level.

Dirty heads

Q. Will a less expensive tape player, or dirty heads, or worn heads, or magnetized heads ruin or destroy part of the sound on a tape when the tape is played back on such equipment?

-(Tim Erickson, APO San Francisco)

A. Magnetized heads, or any other magnetized body which the tape contacts, will tend to erase the sound on the tape, particularly the higher frequencies. Also, magnetized objects tend to add noise to the tape.

Bias switching

Q. I am going to buy a new tape deck this year and am specifically interested in a deck that has a bias switch to change from low-noise tape to regular tape. In your opinion, does a switch such as this actually work well without the equalization being changed?

-(Robert A. Ward, Cleveland Heights, Ohio)

A. I see no reason why the bias switch should not work well. If there are no simultaneous changes in equalization (treble boost should be somewhat less for low-noise tape) and in record drive current (should be somewhat more for low-noise tape), the chances are that the manufacturer has adopted a compromise setting for the bias change, so that you are getting most, but perhaps not all, of the benefits of low-noise tape. See what happens if in recording you supply more signal to the tape--about 0.2dB more--when using low-noise tape. If distortion does not go up audibly with an increase in record level, you will have improved on the signal to noise ratio.

Calibrating VU meters

Q. 1 wish to adjust the bias and calibrate the VU meters of my tape recorder, using Sony SLH-180 tape. I have all the necessary equipment. What procedures do I follow?

-(Dennis Thompson, Enid, Oklahoma)

A. If record equalization is fixed, you increase bias as much as possible without undue sacrifice of treble as measured in playback. If record equalization is variable, do the following.

Simultaneously record and play a 1,000 Hz tone (or a 500 Hz tone if the manufacturer of the tape machine recommends this), meanwhile increasing bias until you obtain maximum output in playback. Then further increase the bias until output of the 1,000 Hz signal drops about 1/2 dB. Now adjust record equalization for flattest possible treble response as measured in playback. It may be necessary to make very slight further changes in bias in order to get desirably flat treble response. All this assumes you have first cleaned and demagnetized the heads and adjusted them for correct azimuth alignment.

The VU meter should be adjusted to read 0 VU when recording a 400 Hz signal at a level that produces 1% harmonic distortion as measured in playback. If by chance the meter is a peak reading rather than average reading device, then the reference level should be 3% harmonic distortion instead.

Storing tapes

Q. What is the proper way and place for storing my tapes?

-(John W. Ross, Campbell, California)

A. It is advisable to store tapes under conditions approximating "normal room temperature" and free of excessive humidity or dryness. It is preferable to store tapes end up rather than flat. After a tape has been recorded, it is advisable to store it tail out--that is, with the last part of the recording at the outside of the reel.

This tends to reduce apparent print through during storage. And it tends to relieve stresses that accumulate during storage, because the tape has to be rewound prior to playing. High winding speeds tend to create stresses that may distort the tape during long storage. Hence if long storage is contemplated, it is desirable that the tape be stored after operation at normal speed rather than at high winding speed.

More on Low-noise tapes

Q. My questions concern the tapes which are designated as low-noise, high output. I am aware that a machine must be specifically equalized and biased for a particular tape in order to realize the potential of that tape. But if one has a machine whose bias and equalization are set for Scotch 203 or its equivalent, then: (1) What type of performance can one expect from these tapes; (2) Will is make a difference as to what speed is used? (3) Are there any tests one can make to judge a tape's performance so comparisons can be made? (4) What effect does Dolbyization of the signal have on the tape's performance?

-(Gilbert J. Hansen, Pittsburgh. Pennsylvania)

A. If a machine is set for Scotch 203, it will work approximately right with other low-noise tapes. Generally, tape manufacturers try to make tape of a given type competitive with each other. However, one will find some differences with respect to frequency response, distortion, and signal to noise ratio. Sometimes these differences will be measurable but inaudible, and sometimes they may be great enough to be audible. Suitable test equipment is required to test frequency response, signal to noise ratio, and distortion.

I doubt that the differences, such as they are, will vary according to tape speed. For example, if Tape A is 2-dB better than Tape B with respect to signal to noise ratio at 1 7/8 ips, Tape A will tend to be about the same amount better at 3 3/4 ips. I doubt that the Dolby system changes the performance of one tape relative to another.

Buying a tape deck

Q. I am in the process of buying a tape deck. I would like to make full use of all its capabilities, and being a novice in the tape world would appreciate any advice you could give me. Also, indicate any books or articles from which I could derive the necessary information.

-(Terry L. Piotrowski, Brook Park, Ohio)

A. Your question is so broad that I can give you only a very general answer. Visit your local audio store(s) and see what books they have Ion tape recorders. Visit your local library and hunt through back issues of audio and electronic magazines for articles about tape recording. Carefully read the manual that comes with your tape deck.

In purchasing a tape machine, make sure you hear it before you buy it. Take along a phono disc known to be of high quality, and ask to have parts of it copied on tape. Compare the tape playback with the disc; if possible, make it a simultaneous rather than sequential comparison. Keep your ears open for significant difference in frequency response, for pronounced hum and/or hiss, for audible distortion (coarseness or graininess of sound, or a veiled quality), for detectable wow (which causes steady tones, such as those of a piano, to go "sour"); in short, for anything you don't hear on the disc.

(Audio magazine, Feb. 1973; Herman Burstein)

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