I mean this is true but not about the '70s as the original post states. Even by the '60s they had sophisticated stereo audio mixers - they just cost hundreds of thousands of dollars instead of running on people's phones like today.

[–] prole@lemmy.blahaj.zone 4 points 1 week ago

Yeah, we had stereo mixing/mastering pretty much down by the 70s I think...

What I think OP might be referring to are albums that were recorded in mono in the 60s, and then released again in stereo in the 70s when the tech only allowed for full L or R panning. Those albums were never meant to be listened in anything but mono though.