I doubt much electronic manipulation was available that long ago. To me, what explains it was that we were idealistic, wanted to feel it, and were heavily conditioned to have the familiar songs and setting put us into "bliss". The music definitely helped the mood at events. (But music can be magic for eons past and present, unrelated to Rawat.)
Personally, I felt that exact kind of high whenever I saw him or listened to him - even if just an audio tape, movie, video, or whatever. When he wasn't there it had less intensity than in person, but was the same. I think it was belief and conditioning.
Heck, I felt that same "high" the first time I went to an ashram satsang 2 or 3 months before I received Knowledge, and no one "special" was there other than the local premies. I'd never even heard his physical voice (which was somewhat squawky and high pitched at the time, as it turned out.)
I wanted hope during a bleak time when I thought nuclear war and environmental destruction might happen at any time, and it was the answer to my search for meaning in a late-adolescent development phase. And the camaraderie, the aspiration/inspiration/world peace goals, the answer to existential questions, and the whole idealism was so much more wonderful than common place existence as a teenager during the early 70s, which I had previously viewed as somewhat meaningless. No electronic technology required.