Tape Guide (May 1981)

Playback Without Lag

Q. I have an inexpensive open-reel deck with separate record and playback heads. Is there any way I can add Sel Sync when making sound-with-sound recordings so that both channels can be played back without a time lag between them?

-David Wasilewski, Elysburg, Pa.

A. The answer depends on your ability to read circuit diagrams and find your way around your tape machine. What Sel-Sync does is to convert one section of the recording head into a playback head. For example, suppose that you made a recording on track 1 through the left channel. Now you want to make a recording on track 3 through the right channel, in sync with track 1. By switching the left channel of the recording head to the playback mode, you can hear what is on track 1 in sync with what you are recording on track 3. Thus your task is to work out a switching system which connects one channel of your re cording head to the playback electronics instead of to the recording electronics.

Inasmuch as oscillator current will then no longer be going to one channel of the recording head and to one channel of the erase head (which must be partially disabled to prevent erasing the recorded track), you require a substitute load; otherwise the amount of oscillator current going to the active sections of the recording and erase heads will change, adversely affecting your recording.

Intemperate Tape Deck

Q. On a top shelf with more than ample air circulation, my tape deck displays a temperature rise which I feel may be harmful to the tapes and equipment. From an ambient temperature of 86 degrees F, the machine's temperature rises to 110 degrees in less than an hour's operation. I understand that transistors start to lose power at about 90 degrees and that high temperatures adversely affect tapes. Are the temperatures I mentioned excessive with respect to either equipment or tape?

- Edwin Small, Honolulu, Hawaii

A. A number of tape machines run quite hot, sometimes over 110 degrees after an hour or two of operation. To my knowledge, transistors do not significantly change characteristics at a temperature as low as 90 degrees F; they would be unsuited to many purposes if they did. Tapes can stand appreciably elevated temperatures, probably well over 110 degrees. When you see a warning about leaving tapes in a closed car on a warm day, bear in mind that the temperature can easily mount to 1 50 degrees. I doubt that any of your equipment is in danger as long as the temperature mounts to no more than 110 degrees or so. Nonetheless, if you are worried, why not bring the equipment down to a lower shelf where the ambient temperature is lower.

Inimi-TrebleRange

Q. I plan to buy a cassette deck and am curious about the limited treble response of most medium-priced decks. If I am correct, the audible range is up to 17.5 kHz, while most cassette decks record only up to 14 to 16 kHz. Will I be losing audible sound?

- Howard Ross, Columbus, Ohio

A. The human hearing range is said to extend from approximately 20 to 20,000 Hz. Ability to hear frequencies as high as 20 kHz at normal levels probably exists chiefly or entirely among children, and only among relatively few of them. For most adults the upper limit is something like 14 kHz or less, unless the signal is of quite high level. In most music and other program material, little if anything is found at high level much above 14 kHz or so. If a cassette system can maintain flat response to about 14 kHz, it sounds like a reasonably faithful reproducer to most of us. Accordingly, in looking at frequency response specifications, what is important is flat response up to about 14 kHz; what happens above that tends to be of relatively minor importance.

The above, I think, is a consensus; there is no complete unanimity. However, there are a few, the so-called "gold en ears," who can distinguish between a system faithful to, say, 14 kHz, and one faithful to 20 kHz or better. There is a small probability that you are one of these few.

Bass Non Profundo

Q. When I play back 8-track recordings I have made, they have a lack of bass. Please tell me the cause of this problem.

-J. Marquez, Gurabo, P.R.

A. One possibility is the tape you are using. Some tapes, particularly those with extended treble, tend to be deficient in bass. Another possibility is defective playback equalization, owing to a faulty capacitor or resistor. Recording equalization may be defective, and still another possibility is insufficient bias, which would favor high frequencies over low ones.

Trade-In Value

Q. As I understand it, the higher the recording level, the narrower the frequency response. If this is true, doesn't a Dolby noise-reduction system trade some frequency response for quieter performance?

- Bruce Rubin, APO Seattle, Wash.

A. When properly adjusted, the Dolby system does not trade a reduction in noise for a reduction in treble response. Dolby NR applies treble boost in recording only at low signal levels, and therefore it does not increase the danger of tape saturation and consequent loss of treble. In playback, treble cut is applied at low levels, thus restoring flat response and at the same time reducing noise.

The lower the signal level, the greater is the Dolby system's action (record treble boost and playback treble cut). At high levels, Dolby NR is inoperative, and pro gram material tends to mask noise.

Switched-On Bias

Q. I am interested in buying low-noise high-output tape. Will this kind of tape damage my heads? My tape deck does not have a bias switch. Will I still get the low noise and high output that the tape is designed to provide?

-Ronald Harrmann, Columbia, S.C.

A. Such tape will not wear your heads any more than other tapes of high quality. There is a good chance that you will get reasonably satisfactory frequency response with your present bias when using low-noise high-output tape, al though ideally the bias should be in creased somewhat. If you do get a moderate departure from flat response, there is nothing wrong with using the bass and treble controls of your audio system to touch up the response. If the departure is more than moderate, that is, an appreciable increase in treble, it will be necessary to increase the bias.

(Adapted from: Audio magazine, May 1981; Herman Burstein )

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