Tape Guide (Q and A) (Jan. 1970)

by HERMAN BURSTEIN

Q. I have been attempting to run a frequency response curve on my tape recorder. It is my purpose to determine the response of the entire recorder--including the record amplifiers, tape recording heads, playback heads, and the tape itself. I have tried several different methods to accomplish this; all of them involve inserting a sine wave at the input of one channel, recording it, and monitoring the playback amplifier output of the same channel. 'Depending on the procedure used, varying results were obtained in the frequency range below 12 kHz.

With all methods, however, an extremely sharp drop-off was noted above 12 kHz. With this background information in mind, I ask the following questions What is the proper procedure for determining the frequency response of a component tape deck which will take into account the capabilities of the entire tape recorder system?

-Walter B. Pearson, Panama City, Fla.

A. You make no mention of the recording level at which you conducted your tests. In checking the record playback response of a tape machine, it is essential that this be done well below "normal operating level," for otherwise you run into tape saturation, particularly at high frequencies. In typical natural audio material there is usually substantially less audio power at high frequencies than at lower ones. Therefore tape saturation is unlikely to occur even though your record level indicator shows that maximum permissible level has been reached. I suggest that you conduct your tests at a level at least 15 dB below maximum permissible recording level, as shown by your record-level indicator. Further, you do not mention the tape speed at which you conducted your tests. At 7.5 ips, you have the right to expect of a quality machine that it will provide response flat within 2 or 3 dB out to at least 15,000 Hz.

At 3.75 ips, however, you do not have the right to expect much beyond 12,000 Hz unless you are willing to make appreciable sacrifices in terms of distortion and signal-to-noise ratio.

Q. Can you tell me where I can find information on the procedure for optimizing my tape deck for low-noise tape. I would also like to know if plans for a bulk eraser have been printed somewhere.

-David O. Hafemeister, Philadelphia, Pa.

A. Procedures for optimizing bias, record equalization, and record drive current should be obtained from the manufacturer of your tape machine, or from his authorized sales or service agency. In general terms, low-noise tape compared with conventional tape requires slightly greater bias, slightly higher recording level, and slightly less treble boost.

How to construct a bulk eraser from a power transformer was discussed on page 86 of my hook, How To Get the Most Out Of Your Tape Recorder ( John F. Rider Publisher, Inc., 116 W. 14th St., New York, N.Y.) I quote: "Disassemble the transformer, remove the E-shaped and I-shaped plates from the transformer core, re-insert only the E-plates so they all face in the same direction, and reassemble the transformer except for the casing. Attach lamp cord and a plug for the house socket to the leads of the primary winding. Be sure that you know which are the primary leads-usually they are black. Snip all other windings and tape them so they will not make contact with each other. Wind the bulk eraser with friction or rubber tape to protect the core and windings."

Q. I have a question regarding impedance matching of my transistor tape deck when connected to my tube preamplifier. Here are the rated input and output impedances of each to help you decide whether or not they are matched:

Tape deck preamp INPUT is 220k

Tape deck preamp OUTPUT is 10,k

Tube preamp tape INPUT is 250k

Tube preamp tape OUTPUT is 1k terminating at 100k

Actually, I experience no audible troubles with my hookup of these two components, except that when recording a disc to tape I notice a slight decrease in bass response. Electrically, and perhaps audibly, what differences would impedance mis-matching produce? I have been told that as long as the INPUT of any component is higher than the source OUTPUT there is no need for concern. Is this correct?

-Monte L. Henrie, Casper, Wyoming.

A. The general rule is that as long as the input impedance is at least 10 times the source impedance, the former has no significant effect on the latter with respect to frequency response, distortion, and signal level. Such is the case for your equipment.

As for the slight decrease in bass response when making a tape recording, this is probably due to the equalization circuit of your tape machine, most likely in playback. Seldom is equalization perfect. If one listens hard enough, he can almost always find some minute difference between the original and the copy. It is also true that the bass loss in your tape machine may be deliberate; some manufacturers go somewhat lightly on bass response in playback because by doing so they also reduce hum and thereby improve the signal-to-noise ratio.

Q. A question I have wondered about is what effect the width of a magnetic recording has on the quality of the sound. I know that the frequency response is limited by the speed of the tape, but I don't think I have ever seen anything on width. I can remember when sound was recorded on the full width of 1/4" tape, and now the stereo tapes have four tracks in that space. There are tape cartridges with eight tracks, and I don't think the tape in them is any wider than 1/4". Thank you for any information you can give me.

-Charles L. Anderson, Sacramento, Calif.

A. A wide track (say the full width of the tape has the following characteristics relative to a narrow track (say 1/6th the width of the tape, allowing for three blank islands between four recorded tracks): (1) Higher signal-to-noise ratio because more information can he recorded on a wider track.

(2) Greater freedom from dropouts because the wider track permits more room for tape imperfections to cancel out. (3) Less volume variation owing to changes in contact between the head and the tape. (4) Greater treble loss in case of azimuth misalignment; for a given degree of azimuth misalignment, the narrower the track the less is the treble loss.

Q. I am planning to make a trip to Hawaii or Mexico and want to use a portable tape recorder to record the trip. Do you have to have a more sensitive mike than that comes with this tape machine?

-Vern E. Long, Cleveland, Ohio.

A. Generally the microphone that comes with a tape recorder has sufficient sensitivity, although it may not have the width and smoothness of frequency-response characteristic of a high-grade microphone.

Q. I am very interested in tape recording and in tape duplication. Are there any laws concerning duplication for personal use and for small re-sale?

-(Name Withheld)

A. There certainly are laws concerning copying of discs or tapes for resale. Even the practice of copying for personal use is open to legal question, although difficult to restrain in most instances as a practical matter. Also, AUDIO published an article in its May 1964 issue, Tape Recorders and the Copyright Law, that would help you.

Q. I would he much obliged if you would answer some questions about tapes that have been bothering me: (1) For certain purposes where high fidelity is not essential, second-line recording tapes should be suitable. However I have been told that such tapes might damage the tape heads. I would think that if the second-line tapes are rejected standard tapes, then the abrasive properties would be about the same. Am I correct? (2) Some catalog houses sell their own brands of tape.

Can I assume that except for their lowest priced lines (comparable in price to second-line-taped the house brands are equivalent to standard or professional tape as claimed? (3) I have been told that acetate tape will stick together under certain conditions.

Whether or not this happens depends on the hinder it would seem; therefore Mylar tape with the same binder would also stick. Is this right?

-King Lee, Buffalo, N.Y.

A. (1) There is no guarantee that second-line tapes, as you call them, necessarily have the same physical characteristics, such as abrasive quality, as first-line tapes. For one thing, the second-line tape may be made to a price, so that less care is taken in keeping abrasion low. For another, the tape may have been rejected for first-line use because of its abrasive characteristics (as well as for other reasons, perhaps) .

(2) I cannot comment on house brands of tape, partly because of lack of sufficient experience with the myriad of types available.

(3) I do not know whether Mylar has greater or less tendency to stick than does acetate. I have had no difficulty of this sort with either kind of tape, provided it has been of first quality.

Q. It has occurred to me that I could reduce noise of my tape system by turning up the treble while recording and turning it down during playback. Would you comment on this idea? Would the frequency response be reasonably smooth when operating in this manner?

-King Lee,. Buffalo, N.Y.

A. Yes, you could reduce noise by boosting treble in recording and reducing it in playback. In fact, one of the leading manufacturers of tape recorders uses or has used this idea for special purposes (such as tape duplication) , with boost concentrated in the region of about 3000 Hz. However, if you employ ordinary treble boost, becoming ever greater as frequency rises (out to 15,000 or 20,000 Hz), you are likely to run into the problem of excessive distortion owing to increased treble emphasis. Keep in mind that the typical tape recorder already supplies a good deal of treble boost in recording, and if you add to this, the problem of distortion becomes quite serious.

(Audio magazine, Jan. 1970; Herman Burstein)

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