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The Lacquer Channel
The Cutting Head
The Recording Stylus
The Lacquer Disk
The Disk Cutter
Cutting The Disk
Speeds, Grooves & Record Sizes
The Plating Plant
Plating The Lacquer Master
Negative Metal "Matrix" To Positive "Mother"
Stamping To Pressing
Of Shellac And Wax
Vinylite And The Shellac-less Shellac
The "Waffle-Iron" Record Press
Milling And Mixing
In 1952, the distinguished American music/audio writer and critic, Edward Tatnall Canby, wrote a series of articles for The Saturday Review which was published in book form as "The Home Book of Recorded Music and Sound Reproduction", by Prentice - Hall, Inc. New York. As was Canby's usual style (and that of most New York critics of the day), it was pompous, superfluous and mostly talked down to the reader. It covered a lot of ground, and despite containing a number of errors, it still made for interesting reading.
I have adopted Canby's basic framework for this article, along with a lot of re-writing and correction of the obvious mistakes. I have also added much material from my own direct experience as a recording engineer for RCA Victor in the 1960's.
... Graham Newton
To every person who has read the "Technical Information" box on the jacket liner notes of an LP record, the names Scully, Presto, Neumann, Westrex, Grampian, HAECO, Pultec, Langevin, Fairchild, Altec, Capps, Transco, Audio-Devices, Soundcraft and others may be familiar, almost household names.
These were all manufacturers of equipment and supplies that touched the process of making phonograph records, from the stage of being converted from a "master" to a release pressing intended for home playback.
THE LACQUER CHANNEL
It all starts with the disc recorder or "lathe" as it is often referred to... a precision piece of equipment designed with a slowly rotating feed screw mechanism and carriage to uniformly move a cutting head across the radius of the disc. The accurately shaped cutting stylus, mounted in the head, cuts a VERY precise spiral groove across a flat lacquer coated aluminum disc spinning at an exact speed of 33-1/3, 45, or 78.26 revolutions per minute, the standard phonograph operating speeds. Scully, Presto and Neumann are probably the best known manufacturers of disc recording lathes.
There were instances of early recordings (mostly acoustical) that played at speeds as low as 60 rpm, and as high as 90 rpm, but by the time electrical recording replaced acoustical, standard speeds were adopted.
THE CUTTING HEAD
Installed on the lathe, the cutting head is simply a phonograph pickup in reverse, that is, feed audio in and get mechanical motion out. Other than its greater size, the specially shaped cutting stylus, and the feed screw mechanism which moves the head across the record to make the spiral groove, the internal workings are very similar. A great deal of literature has been written about the cutting stylus, its shape and the resulting groove cut by it, many written by engineers Frank and Isabel Capps, whose company produced many of the innovations in disc recording styli over the years, not the least of which was the Capps (ANM) Antinoise Modulation Stylus and the Cappscoop stylus which provided a further 3 dB reduction in noise for stereophonic records.
THE RECORDING STYLUS
Contrary to what you might think, diamond IS NOT a good material for a cutting stylus, but IS excellent as a reproducing stylus. The recording stylus is one of, if not THE most important component of the recording process, and was probably first used by Edison in 1877.
Home cutting styli were often made of a steel alloy called Stellite because it was inexpensive to manufacture, and although cutting styli have been made of other materials, most cutting styli for professional use are made of corundum, commonly known as sapphire.
Because of its lack of grain, crystalline structure and cleavage, sapphire may be ground to very accurate dimensions and angles, while retaining a very fine cutting edge. These properties are of prime importance in manufacturing a recording stylus. Believe it or not, a sapphire recording stylus will outlast a diamond and produce superior recordings.
A small sapphire rod is ground with a flat face and mounted in an aluminum shank to make it easier to install and remove the stylus from the cutting head as the need arises. The end of the sapphire rod is ground to a point with a rounded tip, and extending upwards from the tip, along the flat edge, are tiny burnishing facets that polish the groove as it is cut, producing a quieter groove. These facets are critical since, if ground incorrectly, they will affect not only the signal to noise ratio but also the high frequency response of the recording. High quality recording demands that the stylus noise be typically in the range of 57 to 60 dB below a recorded 1kHz reference level of 7 centimeters.
For microgroove recordings (16-2/3, 33-1/3 and 45 rpm), the recommended cutting stylus tip radius is .00025 inch or less, and for coarse groove recordings (33-1/3 rpm transcriptions and 78 rpm) the recommended radius is .0015 inch. You can see why a 78 played with an LP stylus sounds so bad! For coarse groove recording, the stylus was often mounted with a slight mechanical bias toward the center of the record. This ensured the thread of cut lacquer material or "chip" would be thrown toward the center of the disc thus avoiding fouling the stylus tip.
In both LP and coarse groove recordings, the included angle (that's the angle formed by the groove walls) is 88 degrees plus or minus 5 degrees. The top of the groove is supposed to measure not less than 4 mils across, for a recording to be played with a 2.5 mil stylus, and in the case of LP's played with a 1 mil stylus, no less than 2 mils across at the top.
A tremendous improvement in cutting "fine groove" records occurred with the introduction of the hot stylus. This is no more than a winding of 6 or 7 turns of "Nichrome" resistance wire around the shank of the stylus, near the tip. Connected to a power supply with adjustable current and metering, is used to bring the cutting stylus to a carefully controlled even temperature. The hot stylus momentarily softens the lacquer surface of the recording disc while the groove is being cut. The lacquer thus offers less resistance to the cutting process, the cut is smoother with less distortion, and the necessity for diameter equalization is virtually eliminated, being reduced to about a 2dB difference between the outside to inside of a disc.
THE LACQUER DISC
Over the years, since the days of wax, recording blanks have been called by various names including "instantaneous discs", lacquers", "acetates", "soft-cuts" and others. If there is a "proper" name, it is probably "lacquer" because of the fact that they are lacquer coated with a compound of cellulose nitrate, and acetate had little to do with it, although it has become a common name for a lacquer coated disc, and many professionals still use the term "acetate". Habits are hard to break.
The term "waxing," still persists to this day, even though actual wax is as out of date in disc cutting as the horse and buggy is to the automobile. In the "bad old days" of recording, there was no magnetic tape and the recordings had to be cut originally on huge thick blocks of warmed, essentially beeswax. Modified versions of the old solid block of wax were in use until not long before World War II.
With the acceptance, in the early to mid thirties, of the much more satisfactory lacquer-cutting process, wax went the way of the Dodo bird. Thus, the final product before "processing" became a single lacquered disk onto which the actual recording grooves were cut.
If you are old enough to ever have made an instantaneous recording, those one-of-a-kind records that studios, department stores, vending machines and the like made for you on the spot, you have seen a lacquer disk. It is made of metal (although the very cheap ones had a paper base), usually aluminum, coated with a thin layer of black, smooth, shiny lacquer. For professional master work, the lacquer surface must be perfectly even... just like a black mirror, and as a matter of fact, you can actually see a good reflection of yourself in a lacquer!
Different grades of "blanks" were offered by the manufacturers, distinguished by the evenness of coating and thickness of the metal itself. Simply put, all the discs of a given grade started through the manufacturing process the same way, but subsequent inspection determined the quality level that the disk met before it was shipped out of the plant... a "double face master" being the highest level sold for the highest price. A disc with a blemish on one side, but otherwise master grade would be a "single face master" and sell for less. More blemishes and defects produced lower quality levels that sold for less and less down to the level of the home recording user. Needless to say, for the making of commercial pressed records or radio transcriptions there was only one standard - the best that can be had for the purpose.
THE DISK CUTTER
A high quality professional disc recording lathe system is very impressive, to say the least... accurately controlled to produce grooves that lie precisely even, next to each other, and such that the depth of the groove being cut will remain uniform and exactly as set, throughout the recording.
The mastering engineer controls all aspects of the overhead cutting mechanism, which extends from the outside edge, across the record, to the center pin, like a bridge over water, and from which the recording head with its stylus is lowered to the record surface. The spiraling grooves are cut by moving the head very slowly, across this bridge, usually by a type of screw feed. Think about a home phonograph playing a record, where the arm follows or "tracks" the pre-set grooves in the record. A disc recorder working upon a blank disk, has no such thing to guide it's motion, and so it must be mechanically moved by a special mechanism to cut spiral grooves. Provisions are made to allow speeding up the mechanism to make the faster spirals at the beginning and end of the record, as well as disengaging the feed-screw drive to permit making a "lock" groove at the end of the record. In earlier days, or with less automated professional equipment, the mastering engineer usually did this by turning a small hand operated crank to speed up the spiraling process.
The record grooves are very small, measuring on the order of 2 mils (thousandths of an inch) for microgroove and about 5 mils for coarse groove recordings (transcriptions and 78's). So that the mastering engineer can look at and measure this tiny area, professional disc recording systems come with attached calibrated microscopes, that can be swung over the groove while the record is being cut. Through the microscope a good mastering engineer can quickly determine if the cut is smooth and of the right depth with the grooves far enough apart so as not to interfere with each other. (Sometimes the pattern of one groove, cut too close, may distort the wall of an adjacent groove, giving a strange almost ghostly "echo" that can be heard just before the first sound or after the last sound on some records.)
The continuous thread of cut material that the stylus throws off as the groove is made is called by a few names... chip, swarf, thread and probably a few others, although "chip" was probably the most common. Most home disc recording enthusiasts ran afoul of this exasperating byproduct. On occasion, it would throw itself nicely to one side and lie flat on the disk in neat rows out of harm's way, but far more often, if not attended to, it would entangle itself on each turn with the chip cut on earlier turns. Catching under the stylus, it quickly builds a rat's nest of tangled material which ruins the cut since, while recording, you cannot lift the stylus away from the record in order to clear it without interrupting the recorded sound and the groove itself. "Chip" accumulates static electricity as it is cut from the groove, and it sticks obstinately to anything and everything in sight, but mostly to the uncut lacquer surface that the cutting head is moving towards! A dry paint brush was usually used to push the chip well out of the way of the advancing cutter head.
Chip is flammable, and can, if a quantity of it is burned, produce a surprising amount of acrid white smoke. Practical jokers working for radio stations were known to take the chip pot from the disc recording room, and set it inside the door of an announce studio just as a long newscast had started, tossing a match in the pot and let it fizzle and sputter producing volumes of smoke to fill the studio to the exasperation of the poor news reader who desperately tried to keep his composure!
The solution to the chip problem for the professional was fairly easy. A
small flared pipe mounted near the inside edge of the cutting head was
connected to a vacuum system. This drew in the chip, swallowed it whole,
and captured it into a large bottle of water for flammability protection.
The chip nevertheless can still make agonizing trouble. Many a record
master has been spoiled by chip at the last minute when all else was
CUTTING THE DISK
Once started on its spiral course, a cutting stylus cannot be stopped without ruining the disk. Everything must be pre-set and double-checked beforehand, from the visual selection and flatness of the disc blank, to the condition of the sapphire cutting stylus, chip suction and all the audio connections and settings. An appropriate size recording disc blank is chosen... usually 14" diameter for a 12" final disc size. A silent groove test cut is made, outside the diameter of the finished disc. This is examined under the microscope to check for correct groove size, and sometimes played back to ensure that the noise level is appropriately low. Sometimes discs are rejected at this stage, or even a cutting stylus might be changed, before things are ready to begin the actual recording.The vacuum pump is started, tape players are cued to the beginning of the recording, the cutting turntable set rolling, and, when all is ready, the stylus is carefully lowered to the record surface, the fast beginning lead-in spiral is cut, the tape playback is started a turn or two after the spiral has ceased, the audio feed to the disc recorder is enabled, and the record is on its way. Depth of cut is periodically checked through the microscope, and of course the volume levels must be watched even though automatic variable pitch will protect against most instances of overcutting to adjacent grooves, there are still the odd nasty surprises that get past the tape mastering engineers. The running time must be checked at the 1/4, 1/2 and 3/4 way through, to ensure that the disc reaches the desired end point necessary for standardization of the finished product.
At the end of the record, after about two blank revolutions, the final spiral lead-out groove is made, again by speeding up the lead screw of the cutting lathe, either automatically or manually, followed by a lock groove. In earlier times, an eccentric lock groove was added on a special machine designed for this purpose. The master is now done, except that it must be visually examined very closely for flaws... once made, it is NEVER played.
For moving to the processing plant, masters are bolted by their center holes into an elaborate box with separations that keep the actual surfaces from touching; lacquer is extremely delicate and easily scratched. (Masters are conveniently stamped or marked for identification in this manner with a scratching stylus, the marks appearing on every finished disk.)
SPEEDS, GROOVES AND RECORD SIZES
There are only minor differences between records, other than the most obvious of size and speed, from 7" 45 rpm through to the 16" 33 rpm transcriptions once used by broadcasters. The greatest differences, however, are found in the groove sizes. Coarse groove 16" radio transcriptions used a slightly narrower and more closely packed groove than the average 78 "standard", but it is played at 33 rpm. The groove used for LP's and 45's is smaller still, and much more closely packed. The problems of groove accuracy with LP's are greater in all respects, than with the old larger groove, and for a while after the debut of the LP in 1948, there were dire mutterings and groanings throughout the industry that small groove cutting was all but impossible.
After unheralded agonies of experiment and slow experience, the cutting of small grooves became less terrifying, and ultimately, no more trouble in this area than the old, and with minor adjustments to stylus size and depth of cut, any sort of record may be cut on the same equipment.
The record mastering engineers are usually found in the studio environment but the plating, pressing and manufacturing of the actual record is usually done at another location. Once the finished lacquer is in its shipping box we enter a new world, a world of more or less mass reproduction, where the object is the making of many from one.
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