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How LPs Are Made
Understanding the art of cutting and pressing vinyl
By Scott Dorsey

CD sales are diminishing worldwide, while the niche markets of new vinyl pressings are expanding. Maybe you, too, should know how the process of making records works?

When you were a kid, did you ever ask where babies come from, and get a circuitous answer that didn’t really say anything? Now that you’re older, have you asked where vinyl comes from, and got pretty much the same answer? Well, I am here to set the record straight in plain and clinical language, with help from some friends at Europadisk and Music Industries.

Mastering

When your music arrives at the plant, a mastering engineer (in-house or outside) first creates an acetate lacquer with grooves on it from your master. This mastering does not produce a straight 1:1 copy; limitations to the vinyl medium require lots of processing before the signal can be sent to a lathe for cutting.

Limitations to overcome

Pre-emphasis equalization is applied (and de-emphasis applied in playback), to get a flat noise floor and reasonable low-end response without the needle jumping out of the groove. (This is why you can’t just plug your turntable into a preamp/mixer/receiver and expect it to work right; the phono preamp has the de-emphasis equalization). This means that the amount of headroom varies a lot with frequency.

The amount of headroom also varies with the position in the stereo field, because the groove is cut in such a way that the horizontal plane of the groove records the mono signal, while the vertical plane records the L–R signal, the difference between the two channels, so that a stereo signal can be recovered in playback.

This is why it is so important to keep bass-heavy signals like bass and kick drum in the center of the stereo field; it’s much harder for the engineer to cut a playable disc otherwise.

How wide the groove?

There is a constant tradeoff between the levels and the running time. The wider the grooves are spaced, the shorter the running time and the higher the levels possible. A lot of quick 12" singles are done with a groove of constant pitch (the distance between each pass of the stylus and the next), because it’s easier for the mastering engineer to work with. If you need to get higher levels and signals with wider dynamic range, it’s routine for the engineer to adjust the groove pitch as the disc is being cut, so louder sections have a coarser pitch than quieter sections. This can be done automatically with a margin control computer, or it can be done by hand, or it can be done with a combination of these methods. In either case, the skill of the mastering engineer directly determines the quality of the compromise obtained.

The linear velocity of the needle in the groove is much slower near the end of the record than at the beginning. This means the frequency response is audibly different on the inner tracks, and it is also more difficult for playback styli to track well on the inner grooves. This is why it’s always a good idea to end each side with a quiet song. Even so, there is still a lot of tinkering to be done.

A job for experts

This mostly subjective work needs to be done by a skilled mastering engineer who knows his lathe and who is looking at the groove as it is being cut. It’s better to have one expert to do it all, knowing what compromises are required, rather than having separate places do the “pre-mastering” processing and the cutting of the lacquer.

You can get away with a lot of stuff pressing a CD that just won’t work cutting an LP. If relatively inexperienced operators add anything to the stereo mix that is not perfectly balanced between channels, they can cause channel imbalances that wouldn’t even be noticeable on a CD pressing, but which can make it much more difficult to cut an LP. If you use an equalizer on both channels and have a slightly different setting on one of the channels, you wind up adding level to the L–R difference signal, making it that much more difficult to cut for that reason.

This is why the LP mastering guys have equalizers and compressors with calibrated detents. They also have phase meters which provide an actual plot of the phase differences between channels on an oscilloscope screen, and often some gadgets to work around these problems (like crossover networks that allow them to collapse the whole bottom end to mono if necessary, and compressors like the Fairchild 670 which can compress the mono and L–R channels separately).

The mastering engineer also needs to have very high-grade monitor systems, considerably better than what you’d find in a studio, so he can hear what is going on, especially with the low end. And of course, the room is usually designed specifically around the speaker system for accurate reproduction.

Cutting—acetate or DMM

The mastering engineer operates a lathe that cuts directly into an acetate master blank—a sheet of aluminum coated with an acetate plastic. It uses a heated sapphire stylus that glides through the acetate, rather than tearing, in a cutting head that is more or less like an oversized phono cartridge operating in reverse.

All of the processing has to be done in real time—the entire side must be cut in one take, without stopping. As a result, the mastering desk usually has two completely separate processing chains. One chain is in use at any given time, and the other one can be adjusted for the next track while it’s operating. Swapping from one to the other and cutting the coarsely-grooved separation between tracks is normally done manually.

The operator cuts one disc per record side, and then he hand-scribes the catalogue and pressing numbers on the inner lead-out groove of the disc. If you ask him, he’ll probably be willing to add to the lead-out whatever other information you want, such as the label name or bad jokes. He also usually puts his initials, signature, or some stamp on the inner lead-out.

The mastering house may give you the option of DMM an>, Direct Metal Mastering. This is a process where the lathe cuts directly into a copper plate rather than into an acetate disc. It has a very different top-end quality. As a result, the processing required in the mastering room is somewhat different. Some people like the more etched and detailed top end of DMM, other people don’t.

Either way, what you come back with from the mastering room is a pair of master disc recordings with the actual grooves on the surface and catalogue numbers scribed on the lead-out groove.

Lacquer preparation

The original lacquer can be played, but even one playing will damage it slightly and it’s generally a bad idea to play it for testing purposes. When the lacquer is sent to the pressing plant, its operator may stamp another set of house numbers on the lead-out groove next to your numbers.

The pressing plant people may consider it necessary to perform dehorning on your acetate. If a groove is cut very deeply into acetate, the edges of the groove may be forced up above the normal level of the record like berms around a ditch. This makes it very difficult to get a good plating off of the disc and these records must be dehorned. Dehorning is the process of running a very fine knife across the surface of the disc and cutting these horns down to the normal surface of the record. Dehorning almost always reduces the noise floor of the disc and it almost always increases the distortion a little bit, so it’s a compromise at all times. Sometimes it is absolutely necessary, and how to do this is entirely up to the judgement of the plating technicians at the pressing plant.

Some pressing plants will also go through a cleaning process for lacquers sent in from outside mastering engineers. Other plants will tell you this does more harm than good, presumably on the assumption that the less you do to a lacquer, the better.

Plating

After the acetate lacquer disc has been checked in, it’s first given a very thin coating of metallic silver to make electroplating possible. This is done to make the surface conductive; of course this isn’t needed with a DMM disc which is made of copper, so the surface is already conductive. The disc is then put into a plating bath, and a very thick and heavy layer of nickel is plated onto it.

One-step

If the disc is being plated with the “one-step” process, sometimes this nickel plating is made thicker with a second plating stage, and it is separated from the disc to make the metal stamper, a direct negative image of the original master, with raised ridges where the master had grooves.

The master is destroyed in the separating process. The stamper only lasts for about 1500 records (though a lot of folks, especially in the classical world, will only allow runs of a thousand). As a result, if you want to press large runs of records you either have to cut multiple master discs (bad idea), or use the “two-step” plating process.

Two-step

In the two-step process, the element plated off of the master lacquer is called the metal master and is usually a bit thinner. It is then covered with a thin layer of plastic or grease, resilvered, and then replated to make another disc called the metal mother. The plastic or grease is used so that the mother can be easily separated from the metal master, and the way it’s applied is critical because it’s very easy to lose detail in the process. The mother is then repeatedly plated in order to make any number of stampers, and the metal master is kept so that any number of new mothers can be made. In this way huge numbers of stampers can be made from a single master, and then even larger numbers of discs made.

The two-step process produces discs that sound a little bit poorer than those made with the one-step process, because slight detail is lost from the additional generations of molding. So there is always a compromise between getting large runs versus the best possible sound.

An advantage of DMM is that the original copper disc can be treated like a mother and reused, unlike acetate lacquers that have to be discarded after being plated. This means a huge number of stampers can be made directly from the DMM plate.

Trade secrets

Some pressing plants contract out the difficult and messy plating process. If the disc is plated too quickly, the nickel surface is grainy and noisy, but if it’s plated too slowly, high-frequency details will be lost.

Every plating engineer has his own formulae and they are all different. For many years, details of plating procedures were very tightly held and pressing plants were very worried of their secret methods being stolen, but in the modern era there has been a lot more openness here, and a lot of engineers have had a chance to compare some of the secret methods being used (can you believe Coca-Cola was added to plating baths at one major label plant in the seventies?).

Stamper preparation

With the stamper dried off, the back of it is polished clean and flat. Then the exact center point is found, marked, and a hole punched in it. Finding the center point is extremely critical because if it’s even a millimeter off, the record will be produced with an audible “wow” in it.

If the two-step process is being used, individual mothers will usually be marked with numbers, so that you can tell from which one a given pressing has been.

The stamper is also played on a turntable with a V-shaped notch in the stylus, which rides the top of the groove, to test for clicks and pops due to defects in the plating. If these are found they are usually repaired by hand with a tiny dental pick. After this, the stampers are ready to go off for pressing.

Printing

Labels are printed, either at the pressing plant or offsite by a local offset printing company. After printing, many pressing houses bake the labels for a few hours to set the ink so that it does not smear during the pressing process. Some of the lower-grade plants omit this step and just expect the customer to live with slight smearing. The printing quality of the label is very important and makes a difference in how your record looks, especially if you do 12" singles to be released in a white jacket.

Pretty much all the pressing houses have the cardboard for the jackets printed offsite today. For both jackets and labels, they normally get digital files in some layout program format from the customer or an in-house layout artist, and use that for the printing. The customer normally gets a color inkjet proof of the layout to verify that everything is in the right place and the colors are right. You can also order a color key proof which is made from the separation negatives, bu t the accuracy of the inkjet proofs today makes this pretty much unnecessary.

A few pressing plants have in-house high-speed inkjet printing for LP jackets and labels. This is much less expensive for short runs because it doesn’t require the setup time of making negatives and plates that normal offset printing does, but it also looks different, and on longer runs it’s more expensive since the per-print cost is higher even though the setup is lower.

Printing technology changes very quickly, much more so than the rest of the vinyl manufacturing process, so it’s definitely worth asking questions about what is available to you. Many folks offer fancy services like metallic inks, embossing and punching, and next year it’ll almost certainly be different even though the plating and pressing will probably not change.

Pressing

The pressing is normally done with an entirely automated machine system. The technician locks the stampers into place on the press plates, and the mechanical system automatically drops a bottom label, a biscuit of vinyl, and then a top label onto the bottom stamper. The stampers are then quickly heated with steam, the plates pressed together and the vinyl squeezed out, and then the plates are cooled down with cold water. As the vinyl is squeezed across the surface of the stampers, a blade swings around the outer edge to cut off any flash (extra vinyl bits).

This process is absolutely critical. As the vinyl mixture is heated, it produces small bubbles of gas and that gas needs to be given time to escape, otherwise it will leave little cavities in the record surface. Increasing the operating speed of the machine and reducing the amount of time the vinyl spends hot produces noisier pressings, but some plants do this to get product out more quickly. On the other hand, running it too slowly causes uneven pressings.

Flaws

Temperature control is also critical; if the vinyl is not perfectly even and accurate as it spreads out across the surface of the disc there will be tiny radial lines on the surface of the record following the path that the vinyl took as it spread out, and sometimes even uneven filling between the inner and outer sides of the groove if it’s very bad. This not only produces higher noise, but it can also produce much higher tracking distortion.

Careless setup of the cutting blade produces discs with a ragged outer edge, which DJs don’t like at all. And the actual preparation of the vinyl mix is absolutely critical; most mixes are extremely proprietary but contain somewhere between 5% and 10% reground vinyl recovered from flash and rejected pressings. The amount of regrind is critical and pressings made of pure virgin vinyl are apt to be much noisier than pressings with a small amount of regrind added.

Black or color?

The actual vinyl that comes from the factory is clear, and normally a polycarbonate additive is used which turns it black. One side effect of this is smoother flow and therefore lower noise floor. To do colored pressings, a dye is added, but this requires a lot more care in machine setup to get a quiet pressing, because of the lack of the polycarbonate. Colored pressings tend to be noisier, although much depends on the skill of the pressing machine operator.

Many of the newer machines automatically eject the disc and drop it into an inner sleeve and into a box, although this is done manually with some older presses. A lot of people prefer the more manual systems because it gives an opportunity for additional quality control, with people actually inspecting each record as it comes off the line.

Testing 1-2-3

Request test pressings before a full press run. Some plants make them on older, entirely manual “proofing” presses rather than on their normal line. This still gives you a good sense of how the mastering was done but it may not represent the final product exactly. Because so much processing needs to be done in the mastering process and because the entire process involves so much sonic coloration, it is essential that you get test pressings and listen to them carefully.

Packaging

Jackets are folded and readied for the sleeved records, which are inserted inside either automatically or by hand. Some folks prefer keeping this whole procedure manual so that damaged pressings are more easily caught. Spot checks for quality control are also done at this time. Then the records are (optionally) shrink wrapped and sent off to the customer.

Most pressing plants allow you to supply your own jackets, but they may require completely folded and ready jackets, or they may require flat prints on a particular grade of paper that they can run through their folding machines. If you want to do silkscreened, woodblock, or hand-set letterpress jackets, most pressing plants will be happy to accept your jackets, but be aware that your handmade mulberry paper might not go through their folding machine very well and you might pay an additional charge for hand-packaging at some plants.

The Future

Right now, there are only three companies making acetate blanks: Apollo and Transco in the USA and MBC in Japan, but the demand seems to be fairly steady.

Although CD sales are dropping off dramatically right now, vinyl sales still continue steadily and vinyl remains a growing concern. The Music Industries people report selling seven or eight million LPs a year alone, and the popularity isn’t just with dance records. There’s a surprising market in classic rock reissues, audiophile discs, and even classical music.

Record manufacture is a pretty mature technology so you can’t expect too much in the way of future advancements. But, as the technology has become more open and plants have become more willing to share information about their methods and procedures, even if only over drinks at trade shows, there has been quite a bit of process improvement in the past few years at many plants.

On the other hand, the increased demand for vinyl has also led to a lot of operations that churn out records faster than proper quality control allows, and I would expect those problems to grow as well.

It’s a funny little corner of the industry...but, surprisingly enough, it’s actually a growing one.

Many thanks to Don Grossinger in New York City, to the crew at Music Industries in the Netherlands, to Paul Gold and the crew at Brooklyn Phono, and to Kate McDonnell, the Canadian layout guru.

Scott Dorsey (dorsey@recordingmag.com) seems to be fascinated with all things old and hand-crafted in audio, from vinyl records to vacuum-tube electronics.




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