The <i>Blumlein shuffler</i> is an analog processor that extracts left-right phase differences and converts them to left-right level difference. It was suggested by Alan Blumlein in his landmark UK patent 394325 as a tool for preserving stereo information otherwise lost during playback through loudspeakers. There are four steps<br>(1) take the original L+R stereo signal<br>(2) convert L,R to M(id) and S(ide) signals through plain addition/subtraction. M and S are, by design, spaced by exactly 90 degrees<br>(3) shift S 90 degrees, so it becomes in phase with M. This step could only be approximated through all-pas filtering, but it somehow worked in Blumlein's hands<br>(4) add/subtract M(id) and shifted S"(ide) to create new L and R channels. The same principle is used in analog Dolby pro-logic circuitry to steer signal into central channel.
<a href="//commons.wikimedia.org/w/index.php?title=User:Retired_electrician&amp;action=edit&amp;redlink=1" class="new" title="User:Retired electrician (page does not exist)">Retired electrician</a>
<span class="int-own-work" lang="en">Own work</span>