Well, now my curiosity is twitching.
How would one decide the rear channels were swapped on virtually ANY quad recording, save the occasional one where an instrument was panned from back to front or the reverse?
I know symphony orchestras have a fairly standard layout, with violins on the left and cellos on the right, but with a rock or pop recording, what would make someone believe that an instrument location was wrong?
Not asking for a friend.
it's quite tricky to ascertain definitive channel layout on any old Quad mix imho, unless one has master tape box information and even then it's a guide not a God and probably needs double-checking.
there's occasional clues and giveaways, some more glaring than others and when you scrutinise the individual channels in a mix you can sometimes pick up on things you may have missed listening to the Quad as a whole in Surround. many times, i guess it's educated guesswork combined with careful listening you might say?
we know that certain labels assigned the tracks of their 4-channel masters with a FL/FR/RL/RR arrangement (basically every imprint under the CBS umbrella) because it was believed arranging the 4 channels on the tape in Stereo pairs diminished the chances of bleed and preserving Stereo imaging and balances were of vital importance to CBS and their predominant delivery method of vinyl encoded with their SQ system.
with other labels on the other hand (incl. RCA & WEA) you may find arranged tracks on their 4-channel masters in "Side" pairs, i.e. RL/FL/FR/RR.
in that kinda scenario, without tape box channel identification information, it's easy to see why there was sometimes confusion, misinformation and misunderstanding on the subject of channel allocation over the years, especially when it came to 4-channel masters being transferred to modern day 5.1 setups with a FL/FR/C/LFE/RL/RR layout/channel assignment.
we also now know that certain labels (incl ABC/Command) sometimes produced 2 different 4-channel layouts for titles destined for Q8 consumption, 1 with a "C" prefix in the catalogue number (surmised to stand for "Car"!) and the other on a tape with an "H" prefix (suggested to have stood for "Home"!) how kooky is that!?
top men have also since sussed out, with sterling detective work by Steelydave and Mr. Dutton Vocalion, that one of Quad's notable mixing duo's (Dick Bogert & Warren Vincent) were given to mixing in a style closer to ABC's "Car" type tapes, with Bass in Rear Left and Drums in Rear Right and those mixes have their fair share of lovers and loathers! (i'm in the former camp fwiw
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certain theories, for example that diagonal pans must be erroneous because diagonals could foul the fragile SQ encode-decode process turned out to be incorrect and in some instances SQ actually benefitted from diagonal pans. CBS' own guidelines included mixing rules on diagonals, for "Room Centre" panning and 2-channel compatibility.
there's a lot to go into really and i'm conscious we're in a Poll so i should stop there but there's plenty of info on QQ and its all good clean fun!