The vinyl record is basically a round plate engraved by a spiral groove. The incision can be on one side even though it is generally also shown on the opposite side. The incision starts from the outer edge of the disk and ends in a closed loop called a runout or an infinite loop. The sound information that is intended to be reproduced is analogically coded in the groove. The best qualities of vinyl (PVC) compared to shellac has made it possible to reduce the weight of the discs, the thickness of the grooves, decrease the spiral's pitch and lower the rotation speed from 78 to 33⅓ turns, thus obtaining a longer listening time than it reaches about 30 minutes per facade in the Long-Playing (LP), with peaks of about 40 minutes per side to the advantage of the content.
With the lowering of production costs, different formats have been introduced. For example, the 16-inch used in the radio, and with different rotation speeds such as 16.6 revolutions per minute to achieve a longer duration at the expense of sound fidelity. The 16 rpm records were mostly printed in the fifties and sixties and were produced for the American market. The dimensions of a 16 laps, highlighted by the initials LLP, are the same as a 33 rpm (12 or 10-inch) Long Plaing and the duration of the reproduction is about two hours between all the facades. In Italy the production of 16 laps has been decidedly low, only some record companies have produced titles at this speed.
The 78 rpm discs and the first vinyl microgroove discs are monophonic, recorded with a single channel signal. The groove of the spiral has symmetrical edges in the monophonic disk. Over the years, the introduction of innovative techniques has made it possible to engrave in the groove both the channels necessary for a stereo reproduction. The incision of the groove has become asymmetrical in such a way as to be able to distribute the sound on two channels, right and left, while maintaining compatibility with mono devices. Over the years, the significant technological progress in recording techniques has allowed a refinement of the stereo that has made it acquire an unknown spatiality at least until the end of the 60s. The sound becomes three-dimensional through mixing techniques and filters that in addition to doing perceiving the origin of the sound also defines its depth, its environmental positioning.
A timid attempt at three-dimensional mechanical vinyl record was made in the 70s but with little success because it has never imposed a standard that codifies the vinyl media for the so-called Quadrifonico or Quadrifonia sound. A kind of Holophony where the points by diffusion from two became four, with front and back channels, a bit like the surround.
