I think I can clear up a couple of things. The album photo above of "Sundown" I also own. It's not quad. If it was it would say "Quad" or "Quadraphonic" or "SQ" or "QS" somewhere on the album front. Pictured above is a release from Mobile Fidelity SoundLabs, and is a half-speed mastered version of "Sundown". What that means is simple...when a record is mastered from the actual tapes from the recording studio...the tape is played into a lathe which cuts what is known as a "Mother" disc. The "mother" can't be used to stamp out discs because it would wear down too quickly, so the mother is used to stamp out a few "fathers" which then stamp out the disc that you own. Mobile Fidelity slowed down the tape playing into the lathe by half, and in turn slowed down the cutting lathe by half, therefore getting a cleaner, better defined groove...which led to an improvement in the final sound coming out of your stereo.
Quad records contained four channels of information in the grooves. The signal out of the turntable was fed into either a quad capable receiver or a seperate processor which sent the additional information (music) to the rear channels. There were two different ways to do this one was known as "QS" the other was "SQ". You didn't need a special turntable or stylus (needle) to hear quad, since the receiver or processor did the actual decoding. Mobile Fidelity also tended to use more vinyl in thier records making for a heaver, sturdier disc.
That was opposed to RCA's "Dynaflex" records...do any of you have any John Denver records where you can hold the disc between the palms of your hands and shake it, and it behaves like a piece of paper! Dynaflex records always had a lot of surface noise...the Mobile Fidelity discs were always very quiet...as long as you were careful handling them.
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