¡Que siga la fiesta!
In a nutshell, CSG (compatible stereo generator) adds a 90° phase shift to only one channel of a stereo recording.Here is another question. What other A&M albums, if any, had HAECO-CSG and does anyone know what it stands for?
I have looked at some of my A&M records and do not see it. I thought that since the Brasil'66 Greatest Hits had ti that the TJB Greatest would as well but it does not state it. The closest catalog number to Fool On The Hill that I have is Claudine Longet Colours and it does not have it.
The plus side is that if you play the stereo record over a mono system, the level of the center signal (consider a lead instrument or singer centered between the two speakers) will be dropped in level so it does not play back too loudly, due to the electrical summing of both sides.
The minus side is that it sounds weird and "phasey" when played in stereo, and smears where the instruments are placed left to right in the soundstage. (For instance, you might hear the fundamental note of a bass in one place, and the overtones (the "plucking") in another. It's not as bad as a stereo signal being completely out of phase (which over headphones, feels as though your eardrums are getting sucked out of your head), but it's enough to ruin the enjoyment of an album.
The only software I've found with a phase shift feature is made by Izotope, so thankfully I mostly corrected my copies of these albums after I ripped them for the music server.