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Record Pressing

A Short History of audio recording

Thomas Edison is credited with numerous inventions throughout his career as an inventor and scientist. Although, one invention of his gave birth, so to speak, to the music industry .the phonograph. This relatively simple mechanism was created to store an analog wave mechanically. He did this by having a diaphragm control a needle, which then scratched an analog signal onto a tin foil cylinder.

When a sound was made, the diaphragm vibrated --much like a human's vocal chords, causing the needle to vibrate. These vibrations were then scratched onto the tin. Throughout playback, the needle moved over those scratches or grooves, creating vibrations that made the diaphragm vibrate and re-create the sound.

The gramophone's major improvement on this was the use of records with a flat groove making mass production relatively easy.

The next step was to record the music onto magnetic tape, giving a higher quality of sound reproduction. And, of course, now we record the music digitally and optically, giving a higher standard of reproduction yet.

The manufacturing process, however, remains essentially the same as it has for years, from lacquer cutting to pressing.

Vinyl Album Manufacturing

An artist's master recording is first transferred to a disc, called a "lacquer", which is 14 inches in diameter. To accomplish this, a cutting lathe is used to shape the disc. These discs are actually lacquer-coated aluminum and are often referred to as acetates.

The lathe has a turntable upon which the lacquer is placed, but instead of a tone arm with a regular stylus, there is an instrument with a diamond stylus that cuts out the distinct grooves on the lacquer, under the guidance of a computer system.

When the disc is ready to be cut and the parameters set, the lathe moves into the proper diameter. For a 12-inch master disc it moves into 11 7/8 inches, drops the head and makes a fast spiral groove (on the outside, to guide the stylus into the playing area).

The cutting stylus cuts anything that is completely left side information, although the stylus itself is vertical, at a 45* angle to the left. Anything it sees as right side information is cut at a 45* angle in a plane to the right. Anything it sees as lying in the center of the two speakers is cut completely horizontally. Any sound occurring completely in the right speaker, not appearing in the left speaker, or vice-versa, is called vertical information: the stylus moves in an up and down motion.

When the master tape indicates a space, the lathe automatically puts a small spread between the tunes. After reaching the inner diameter and the cutting is finished, the machine puts in a spiral and a lock groove, ties it off and lifts the cutting head.

When the master is complete it is microscopically inspected and shipped to a pressing plant.
At the plant, the lacquer is electroplated. When this coating is thick enough it is peeled off to create a 'metal master' which is now a negative image of what was on the lacquer (it has ridges where the grooves go).

Several "mothers" are made from the metal master (again by electroplating) which are intermediate masters, and positive images again.

The process is repeated again to form negative discs called "stampers". These stampers, which have refinements like a depression around the edge to make the raised outer rims of the discs, are the "molds" with which the grooves are actually stamped on vinyl under heat and pressure.

With this three step process, involving metal masters and mothers, you can make as many discs as possible from a single lacquer; otherwise the tricky process of lacquer-cutting would have to be repeated almost continuously, increasing the likelihood of inconsistency in the finished product.