THE KINDEST CUT
Manufacturing CDs is very easy. All you need is one or more disc mastering systems to produce CD masters, injection molding machines to form the disc substrate, metalizing systems to apply the reflective coating, spin coaters for the top acrylic layer, printing machines for labeling, quality control to spot problems, and packaging machines to put discs in jewel boxes. You also need a few hundred skilled workers and a couple thousand square feet of clean rooms in which to put them and the machines. A "clean room" involves more than a good vacuuming. CD manufacturing clean rooms are about 1,000 times cleaner than hospital operating rooms, which in turn are about 100,000 times cleaner than my desk.
After a year of planning, six months of construction, six months of debugging, and $10 million to $20 million worth of investment, it is very easy to make a Compact Disc. What's the big deal? You are only mass-producing objects with a spiral of precisely arranged pits--2,or 3 billion of them, each the size of a bacterium.
Irony aside, CD manufacturing is tricky and expensive. That's why a CD pressing plant may charge more than $1,000 to master a disc and $3 for each disc manufactured (including the jewel box). Given this high initial cost, it is not surprising that a disc costs more than $15 by the time it reaches you.
That bottom-line price is why CD lovers everywhere should stay tuned in to CD manufacturing technology. As new technology is developed, efficiency should rise and costs should fall which should result in better disc avail ability and lower prices.
The latest piece of CD manufacturing news comes, curiously, from a company renowned for its work with LPs: Teldec Schallplatten GmbH, a record company with headquarters in Hamburg and laboratories in West Berlin. Although my colleagues Bert Whyte, B. V. Pisha and George Alexandrovich, and Leonard Feldman have previously described Teldec's Direct Metal Mastering process (December 1986 and April 1987 issues), I think the DMM technology is so innovative that it deserves yet another look. But first let's review analog LP mastering, from which DMM-CD is derived.
Conventional analog LP mastering starts with a master disc made of aluminum, coated on one side with a lacquer material made of cellulose nitrate, plasticizers such as castor oil, and dyes. A heated cutting stylus, its motions modulated by the input audio signal, chisels the spiral groove on the lacquer. A silver layer is applied to the master lacquer, and then the disc is electroplated with nickel. This new metal master is electroplated again to form a metal "mother." A final electro plating process results in stampers which press the vinyl disc.
Teldec is famous for its DMM technology for LPs, a process in which the groove is cut directly into copper using a diamond cutting stylus. Since copper is much harder than the lacquer paint on conventional LP masters, the DMM groove has sharper definition and is not subject to the effects of time and temperature. DMM also eliminates the need for silvering, a problematic pro cess, as well as the first electroplating step.
Masters cut with DMM yield LPs in which groove echo is virtually eliminated, groove noise is reduced, high-frequency detail is enhanced, S/N is in creased by up to 10 dB, and playing time may be increased by up to 15%. It may be no coincidence that about one third of the first 100 LPs on a recent Billboard "Top Pop Albums" chart are DMM discs. These include the live Springsteen album, Paul Simon's Graceland, and Steve Winwood's Back in the High Life.
Now Teldec has announced a DMM CD process for producing Compact Disc masters. They claim lower investment and production costs compared to conventional CD mastering systems employing photoresist methods. Unlike DMM-LP mastering, DMM-CD will not yield a higher fidelity CD, but Teldec claims that their process results in fewer bit errors on the master.
A conventional photoresist CD-mastering lathé uses a laser beam to ex pose a photosensitive layer on a glass plate. When the layer is developed, the pit structure appears. Metalization techniques (similar to those used for LPs) yield the metal molds which are used to replicate discs via injection molding of polycarbonate plastic.
The circular spot the laser projects on the photoresist layer, and the photoresist development itself, result in a pit with rounded contours. Likewise, the finished CD has rounded pits with a depth approximately one-quarter the wavelength of the pickup's laser beam.
This laser beam is reflected with high intensity when it strikes the mirror-like disc surface between pits. When the beam strikes a pit, the round trip in and out lengthens the beam's path by one half wavelength, causing phase cancellation and reducing reflected-light intensity. Thus, binary data is read from the disc.
It is crucial that CDs replicated from a Teldec master be playable on regular CD players. In other words, the pickup's laser beam must respond the same way to pits formed by embossing as it does to pits created by photoresist methods. If you take a close look, the embossed pits produced by the Teldec process look a lot like analog record grooves. The cross-section is a "V" with walls at a 45° angle. Teldec determined the correct stylus angle and optimized the speed with which the cutting stylus moves so that the resulting pits would modulate the pick up's laser beam with the same intensity and almost the same phase characteristics as the pits from conventionally mastered CDs. Teldec states that a player pickup built according to the CD standard cannot distinguish be tween the two types of pits.
There is another difference between these pits. The pits on a disc replicated from a conventional master have a smooth profile because the polycarbonate cannot conform exactly to the mold geometry. When a pit is em bossed, however, a ridge is created along the sides of the pit. A stamper with these ridges is said to encourage polycarbonate flow during injection molding, producing relatively sharp pit edges on the finished disc. Teldec hopes that this will result in cleaner finished pits and fewer data errors.
According to Teldec, a primary advantage of DMM-CD mastering is its indifference to dirt. The conventional mastering process requires a clean-room environment because the slightest speck of dust would disrupt the laser beam on its path to the master disc. With DMM, the stylus is in mechanical contact with the master disc and indeed exerts tremendous pres sure when it embosses a pit. Surface contamination (within reasonable limits) is pushed aside when the stylus punches its pit. Teldec engineers tell me that their prototype CD mastering system is operating in their lab next to an open window overlooking urban Berlin-not particularly clean! In comparison to photoresist CD mastering, DMM seems relatively straightforward. And the most straight forward solution to an engineering problem is usually the best solution, because it is the most cost-effective.
Convinced of the cost-effectiveness of DMM-CD, Teldec hopes that some mastering studios will invest in the new system in the same way that some LP mastering studios have their own analog cutting lathes. This would be a big step forward for CD manufacturing, a process hitherto confined to high-tech factories. However, the price tag for DMM-CD, estimated at $500,000 to $750,000, will deter most studios from taking the plunge. Even though such overhead costs as clean-room construction and maintenance are reduced, CD mastering will remain a tricky and relatively expensive operation. Given the engineering demands of CD mastering, it is hard to believe that any system will fundamentally change this.
In addition, I think there is a philosophical difference between CD and LP mastering. LP mastering is widely regarded as a final part of the mixing process, a stage when last-minute technical and even artistic decisions may be made. CD mastering, on the other hand, is strictly a data transcription process; all decisions have al ready been made. Since no production decisions are involved in CD mastering, it is, arguably, best left to the mastering technician at the CD factory.
Where will the Teldec system fit in? It offers an alternative for manufacturing facilities ready to expand their mastering capacity to meet demand. The Teldec system certainly appears to be more cost-effective than the Sony and Philips mastering systems. It may also be competitive with several highly efficient photoresist mastering systems recently developed by U.S. companies such as the Optical Disc Corp.
Of course, there's no telling how the magical properties attributed to DMM LP mastering will help the industry's perception of DMM-CD when it be comes available this summer. That may be the single biggest factor contributing to its success or failure.
If nothing else, DMM-CD is an ingenious and cost-effective system that contributes to the increasingly vigorous industry of new CD manufacturing equipment. In short, second-generation CD manufacturing technology is on the way. In the same way that second- and third-generation player technology helped decrease player cost while improving performance, this new manufacturing technology should help do the same for discs.
For those of us with dirty rooms, there may be hope after all.
(by KEN POHLMANN; adapted from Audio magazine, June 1987)
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