One little tale was quite hilarious. Rick Parfitt was telling of the recording of “Pictures of Matchstick men”. He said that the engineer asked him “Do you want some phasing?”. Upon getting a positive answer, the engineer went to a large wheel fixed on the wall of the studio and, with both hands, turned it to achieve the phasing (the whooshing sound liberally sprinkled throughout the record).
It’s a long way from today’s clicking of mice to achieve multitudinous effects.