Another school project. Have you tried google? Don't try to say it isn't for school because if you had any idea what these concepts are about, you wouldn't be asking. It's kind of unwritten policy here not to do people's homework for them.

I just love how the assumption is made that we are all intelligent and knowledgeable, with an encyclopedic recall of innovative recording techniques, specifically within the parameters of 4 suggested topics.

Yet we are incapable of deducing that its your first post and you haven't the slightest idea what the question you are asking means?

I'm interested in pioneering techniques used in audio mixing for the last two decades.

Great. Its good to have interests. I myself am a fisherman and interested in rainbow trout, particularly from the northern hemispheric lakes? Can you help me?

Well, for mois, decades ago I was using "extreme autotuning" (like it's an olympic sport!) by driving the motor speed on my Ampex MM-1100 way up and running off the synch head...WOW!!!!!!!!
And my "wall of sound" was (4) Marshall 1960A/B cab stacks driven by a pair of Marshall Majors fed by a Studer A810 with the Dolby OFF (but the tracks were ENCODED with the Dolby, so that you get that compressed, harsh , hissiness we all loved back then). Then we'd crank the Marshalls all the way up and mic 'em with a pair of Shure Unidynes (ORTF, naturally!). Finally, I'd route the mics through a Cooper Time Cube and out to a Micmix spring reverb...Wow, talk about a rush...better than a Thai stick at Christmas time!