In April 1970, RCA Records announced the first quadraphonic 4-channel 8-track tape cartridges ("Quad-8", later called just Q8). RCA began releasing quadraphonic vinyl recordings in the United States in February 1973, in the CD-4 format developed by its former subsidiary Japan Victor Corporation (JVC), and made commercially practical by Quadracast Systems Inc. (QSI). RCA's trade name became "Quadradisc". The CD-4 format required a special cartridge that had a ±1 db frequency response out to 50 kHz, a CD-4 demodulator which decoded the difference between the front and rear channels from a 30 kHz subcarrier, four separate amplifier channels, and four separate speakers for the left and right front and left and right rear. Both the CD-4 Quadradisc and Quad-8 tape cartridge systems were true discrete 4–4–4 quadraphonic systems. Columbia introduced a quadraphonic matrix system, SQ, which required a decoder, 4-channel amplifier and the four speakers. The SQ system was referred to as a 4–2–4 matrix system. The Warner Music Group labels also adopted Quadradisc, but the format never became popular, and both RCA and Columbia abandoned quadraphonic recording by 1976; some of the RCA sessions were later remastered for (same as Peter Scheiber's original matrix system) and released on CD. This included Charles Gerhardt's acclaimed series of RCA Red Seal albums devoted to classic film scores by Erich Wolfgang Korngold, Alfred Newman, Dimitri Tiomkin, Max Steiner, Franz Waxman, and others, performed by the National Philharmonic Orchestra and recorded in London's Kingsway Hall.