Audioclinic (Jan. 1981)

Cutter Head Production

Q. Why don't pickup manufacturers produce moderately priced cutter heads, inasmuch as the operation of each of these devices is similar?

-A.S. Marroquin, Alice, Tex.

A. I suspect that the greatest single reason for the small production of disc-cutting heads is simply the lack of sufficient demand for the product.

While it is true that the operating principles for both a phonograph pick up and a disc-cutting head are the reciprocal of one another, still you find that a cutting head has to do a considerable amount of work when cutting a groove, particularly at high frequencies. Just as is true for phonograph pickups, the mass must be kept low in a cutter head if good high-frequency cutting is to be achieved. I suppose you can argue that by employing mass production techniques, these problems can be minimized and prices lowered, but it still comes down to the fact that most recording studios do not cut their own discs; instead they rely on the few people who have found this technology interesting enough to pursue. Disc recording requires a considerable degree of mechanical ability if the equipment is to be maintained at moderate costs.

Because of the relatively light demand for cutter heads, those few which are produced sell at a very high price, often above $10,000. Part of this price is to cover all of the research and development costs which made it possible to produce the head in the first place.

Black-ground Noise

Q. I understand that phonograph record manufacturers use lamp black in the vinyl mix used to press discs. I have heard that this lamp black can cause an increase in the background noise level of a disc! Is it true? If so, why do they continue?

-John Buford, Philadelphia, Pa.

A. Properly mixed, lamp black adds only a very slight amount of additional noise. The lamp black is used because the public does not seem willing to accept a transparent record, but there are so many other reasons for noise on pressings that the lamp black problem is not significant in comparison. To keep costs low, the pressing cycle is kept as short as possible. If the cycle is just a little too short, incomplete molding will result, and the background noise will be higher than would be true if more time was al lowed for the pressing of each disc.

Still another source of noise results from a press in poor condition or per haps a stamper being used for a longer time than it should be. Added problems are those which occur during the plating of the master disc; these can result if the plating cycle is rushed.

We could have quieter discs if the stampers are not chrome plated as most are. However, their working life would be considerably shortened by this lack. They also can strain readily during use, with increased background as a consequence.

Take Your Cue

Q. I have noticed some new (to me at least) terms being used, and I would like to know their definitions. The two of particular interest are back cueing and slip cueing as used with regard to playing phonograph records. I would like to know what they mean as far as the mechanics go, and what their effect is when used. In addition, if there are other well-defined "cueing" conditions, please explain them, too.

-Richard Fink, Lyons, N.J.

A. Back cueing refers to a means by which you can insure a precise start when playing a phonograph record.

An example of this would be a DJ who announces the title of a selection, and just as his words trail off, we hear the first notes of the music.

What is done is to put the tonearm on the record and allow the turntable to spin until the music just starts. The DJ or engineer immediately does one of two things. He may simply grasp the edge of the disc and turn it backwards to perhaps a half turn before the start of the 'first note, and hold it that way, with the turntable rotating, until the time the song is to start. At this time he releases the disc and fades up the volume control associated with that turntable. The music starts cleanly. (If the control was not faded up, but simply left up all the time, the sound of the table moving under the stationary disc would be heard under the announcer's voice.) The second procedure is similar to the first: The engineer lets the music just begin; he stops the table and rotates the table manually back a half turn or perhaps somewhat more.

Again, at the proper time, he starts the table. This latter procedure can be done only if the table is capable of coming up to speed very quickly. Many of the turntables used in home entertainment systems do not come up to speed that quickly. In fact, their motors have low torque, too little for them to come up to speed quickly or even to maintain their speed while an engineer grasps the edge of a disc with the table rotating. In the case of a broadcast turntable, the mat is made of felt and not rubber.

What I have described are two means of insuring the start of a phono graph record at a prescribed time. Each involves the rotation of the disc back ward from the start of the music; this process is known as back cueing. Slip cueing is the first form of back cueing that I described, where the turntable is moving while the engineer holds the edge of the disc.

You will not be able to tell which technique is used when listening to a radio station or to a DJ cueing. The choice depends on the style of the operator, the equipment he is using, and what it will permit him to do.

For a number of reasons, most radio stations these days do not use either of the cueing techniques I have de scribed. The songs are usually recorded onto a cartridge, similar to an eight-track cartridge. Such broadcast "carts" can be cued very accurately by means of special tones which automatically insure that when the engineer starts the "cart" machine, the song will commence instantly, with no "wowing in." Up to this point our discussion has dealt with the proper start-up of phonograph records, but it is probably apparent that "cueing" refers to any situation where some given event must begin at a precise time. A motion picture projector in a TV station must start producing sound and pictures at a prescribed time. Because of the problems of such equipment coming up to speed, the projector must often be started 10 seconds earlier than the desired starting time of the audio. If you have noticed the various combi nations of live and taped commentary shown in TV news broadcasts, you will have an idea of the problems of a TV producer, and will realize how amazing it is that so few errors occur during this very highly complicated kind of programming! Audio tapes are often used for programming, and again, they must start at a prescribed time. This is done by back-cueing them in a manner similar to what was done for discs. The reels are actually rocked by hand to the appropriate point ahead of the start of the tape. Here, however, the tape is not slip cued. That procedure would stretch the tape. Fortunately, professional-grade tape machines come up to a speed virtually instantly. There are some, however, which employ what are known as "inertia wheels" and these machines do not come up to speed quickly. (Inertia wheels are used to stabilize the tape and minimize wow and flutter.) In the case of these machines, a means must be found by which to start the tape early or to manually spin the wheel just prior to starting the tape.

(Source: Audio magazine, Jan. 1981; Joseph Giovanelli )

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