 By the time that the most advanced logic system was introduced for SQ, the "Tate Directional Enhancement System", by Martin Willcocks and Peter Scheiber, realized into the superb Tate II 101A decoder by Jim Fosgate, "quad" was already considered a failure.Harman Kardon had an SQ decoder that could change the separation so it was as low between the front channels as the separation between front and rear channel.Some SQ recordings have been released on Compact Disc, especially on early CD editions, on which the original master mix is encoded in SQ.