People. Lots of people. Just like you and me (sort of). What the band did was this. They prepared a bunch of questions, questions like :
Most of the voices are completely anonymous, but the "stoned laughter" (along with the "short, sharp, shock" bit) from 'Brain Damage' are from roadie "Roger the Hat," and the Irish Doorman to Abbey Road is the man saying that "there is no dark side of the moon, really...as a matter of fact it's all dark." Paul and Linda McCartney are among those who were asked questions, but whose answers were not used (they sounded too ordinary and unspontaneous).