This essay by Alan Moore has since been turned into a book. I quoted this segment on LJ years ago, but think it’s worth fishing back out of the memory-hole:
Pornographic playlets could be purchased, ranging from two-person dramas through to full ensemble pieces if the neighbours were agreeable. These publications came with sheet-music, so that if one of the participants were musically inclined then he or she could sit at the piano and provide a vigorous accompaniment to whatever activity was taking place upon the hearth-rug or the horsehair sofa
Also, at the end Moore has tacked on a fairly sensible social/feminist argument for better, not less, porn:
Rather than functioning as a release for our quite ordinary sexual imaginings, porn functions as another social tether, as control-leash, lure and lash combined in one, a cattle-prod that looks just like a carrot. Dangling temptingly before us everywhere we look it leads us on. Then, in the guilty aftermath of our indulgences, it converts handily into a rod of shame with which to flog ourselves.