When Columbia/CBS and Sony developed their Stereo Quadraphonic system (SQ) that system become the leading matrix system and Electro-Voice adapted their decoders so they also could play SQ records as well as Sansui's QS records.
It was recorded on phonograph, tape, and a few CDs, and required a quadraphonic player for playback.
These had evolved as the result of four competing companies (CBS, Sansui, JVC and Nippon Columbia respectively) pursuing their own quadraphonic systems independently.
Quadraphonic recording was used by both classical artists, including Leonard Bernstein and Pierre Boulez, and popular artists such as Barbra Streisand and Carlos Santana.