Quiet Sun, 1975
Mainstream (despite its title) is a progressive rock record. Listen a little closer, though, squint at the liner notes, and you'll see it's a bridge between prog rock and post punk. Sure, it's led by Roxy Music's Phil Manzanera. Of course, Roxy—who were always leaning more towards pop—had been leaving prog further behind each successive year. The drummer on the set is a young chap named Charles Hayward. The same one who would go on to form the most experimental (and tellingly, progish) post punk bands around: This Heat.
Even the edgier side of Quiet Sun's music is a tad too ragged and ramshackle. This isn't the coiled beast of King Crimson nor the precise jazz-rock gymnastics Soft Machine. It's the last track, Rongwrong— the longest and only one with vocals—where proto-punk elements become undeniable. Hayward is no singer, and his approach to that problem is pretty laissez faire.
In a sense, Mainstream, is outside of time: too late and too rambunctious for prog, too early and too virtuosic for punk.