the mastering process
the first step in pressing records involves adjusting the audio signal. the premastering process involved balancing all the levels, making the mix as punchy as possible, and limiting extreme frequencies that could upset the mastering lathe.
when the lathe cuts the laquer master, the cutting head vibrates up and down and side to side as it creates the groove. the space between grooves depends on how long you want the side to play. the longer the playback the shallower and narrower the grooves must be. groove width is measured in lines per inch (lpi) and directly affects how loud the finished product will be. the louder, the more side-to-side needle deflection is required and thus the lower the lpi. the mastering engineer makes sure they dont collide and create a skip. too shallow a groove and the needle will jump out on dj back-cues. newer lathes have computer control that adapts inter-groove space adaptively depending on the input signal level. this yields longer playing time but with some material with heavy low end like dance music, the computer could have problems preventing groove collision. some mastering houses switch to old-fashioned constant lpi when cutting dance music to ensure a deep, wide, conservatively spaced groove.
riaa and nab created a specification for physical grooves called standard reference level. all mastering rooms calibrate their equipmeent to this level, and most cut 12" or 10" records at the standard reference level (0db). this is how level relates to playing time for a 33rpm 12":
20min @ 0db
24min @ -3db
28min @ -6db
these numbers work for most music - but dance music, which typically requires a louder pressing, should have lower lpi. for 12"s:
33rpm @ 6db: 12:30 for 12" and 9:55 for 10"
45rpm @ 6db: 9:15 for 12" and 7:15 for 10"
what is the matrix?
after cutting the lacquer the mastering engineer enrgaves the matrix # onto the lacquer master. anything plated off the lacquer master will have this number on it, to help the mastering house keep track of all the piece and identifies the record through the distribution network. is this important? kevin smith, at bill smith custom records, el segundo, ca, tells of a press sitting for a day because there was no a/b marking on the stamper.
step up to the plate
after the mastering house is finished cutting the lacquer master discs - one for each side - typically it ships them to the plating house overnight.
the plating process must start within 2 days of mastering, otherwise lacquer deforms damaging sound quality. the plater cleans the lacquer discs and coats them with a layer of silver to render them electrically conductive. next discs are electroplated with nickel. the plater then separates lacquer from metal creating the (negative) "father plate" casing. a similar process then creates a metal "mother" which in principle can be played on a turntable.
at this point the process bifurcates into a 2-step or 3-step path. in the 2-step process the father becomes the stamper in the pressing of the vinyl records, and the mother is kept as source for future masters. in the 3-step version, the mother is plated to make stamper plates used in the vinyl pressing. the 2-step process can press about 4k-10k records before fathers mothers wear out, after which the mastering process must be repeated. the 3-step process yields 15k-100k records. for independent dance-music releases, the 2-step process suffices since consumer market is small.
in an alternate process, direct metal mastering, or dmm (teldec schallplatten gmbh), the plater cuts the groove directly into 14" copper rather than laquer discs, resulting in a brighter more detailed record with better transient response. the the stampers are made directly from the dmm copper master avoiding the 2-step and 3-step processes altogether. the tradeoffs are that dmm costs more, record grooves are shallower - bass-heavy material may trigger skipping. also some dont like the sound of dmm because of the bright high-end.
familiarity with the artist or label may move a buyer to take a random record out of the bin to give it a listen, but sleeve and label design also matters. colored, clear or blended vinyl records increase pressing costs by about a quarter. a 12" record with a 4" label with a 0.28" hole.
a measured shot of melted pvc is placed between labels and the sandwich is pressed at 300 degrees and 100 tons for 20-45 seconds. the record is cleaned and stacked to cool. after cooling the records are packaged and boxed for shipment to distributors.