Editing Phonograph record (section)

===Stereophonic sound===
[[File:Plattenschrift en.svg|thumb|Decoding the left channel]]

A [[stereophonic]] phonograph provides two channels of audio, one left and one right. This is achieved by adding another vertical dimension of movement to the needle in addition to the horizontal one. As a result, the needle now moves not only left and right, but also up and down. But since those two dimensions do not have the same sensitivity to vibration, the difference needs to be evened out by having each channel take half its information from each direction by turning the channels 45 degrees from horizontal.<ref name=VRS>{{cite web|url=http://www.vinylrecorder.com/stereo.html|title=Stereo disc recording|access-date=4 October 2006|url-status=live|archive-url=https://web.archive.org/web/20060925145519/http://www.vinylrecorder.com/stereo.html|archive-date=25 September 2006}}</ref>

As a result of the 45-degree turn and some [[vector addition]], it can be demonstrated that out of the new horizontal and vertical directions, one would represent the sum of the two channels, and the other representing the difference. Record makers decide to pick the directions such that the traditional horizontal direction codes for the sum. As a result, an ordinary mono disk is decoded correctly as "no difference between channels", and an ordinary mono player would simply play the sum of a stereophonic record without too much loss of information.<ref name=VRS/>

In 1957 the first commercial [[stereo]] two-channel records were issued first by Audio Fidelity followed by a translucent blue vinyl on Bel Canto Records, the first of which was a multi-colored-vinyl sampler featuring A Stereo Tour of Los Angeles narrated by [[Jack Wagner (announcer)|Jack Wagner]] on one side, and a collection of tracks from various Bel Canto albums on the back.<ref>Reed, Peter Hugh (1958). ''American record guide'', p. 205.</ref>