|A documentary on how phonograph records are created. Produced by William J. Ganz for the RCA Victor Company. Public Domain, via Archives.org.|
Practical recording began long before electricity or any of the other related media could be used at all. The original process was all-mechanical, involving physical motion from beginning to end, and continued so from the beginning (1877) right through until the mid-twenties, when electrical circuits born of radio were introduced. "Electrical" recording followed. The recording itself was still, of course, mechanical by reason of the cutting needle, but the pattern was transmitted to the needle electrically. Somewhat later there was "electrical" reproduction of records in the home, the actual re-creating of sound from the record being a matter of mechanical motion, as it still is today. It was the transference of the vibration pattern from source to cutting needle and from playing needle to the loudspeaker that became electrical, and with enormous advantage, too, since in addition to its faithfulness and ease of handling, an electrical pattern can be amplified (made larger) to any degree imaginable, and yet retain its essential shape.
The original concept of recording, as envisioned by Edison, involved the capturing of time in a moving groove, to be traced like a railroad track by a stylus. That conception is still with us today in the disk record. To avoid spreading time over miles and miles of groove length, that groove was from the beginning reduced to a circular path, as one confines hundreds of yards of string to a ball and miles of wire to a reel. Originally the groove made a circular "spiral" path around a cylinder. Only later did the spiral wind in upon itself on the surface of a disk.
An LP record will contain a perfect spiral groove a half mile long that, given the proper mechanical equipment, will support a following stylus-needle for a rigidly accurate slice of time, in utter silence. So also with a half mile magnetic tape, wound upon a plastic reel; and so with the Edison cylinder, the Berliner flat disk, the moving-picture film, and the rest. Time recording comes first. Time is limited by length, extended by more length-one dimension in terms of another.