Stereo-4, also known as EV (from Electro-Voice) or EV-4, was a matrix 4-channel quadraphonic sound system developed in 1970 by Leonard Feldman and Jon Fixler.
[1] The system was heavily promoted by RadioShack stores in the United States, and some record companies released LP albums encoded in this format.
[3] EV decoders were sometimes used to produce pseudo 4-channel effects from 2-channel stereo recordings.
EV more or less disappeared after the SQ Stereo Quadraphonic system was introduced by Columbia/CBS Records in the United States.
Partial list of LP records released with EV encoding.