A lot of stations (at least the ones I managed or set up) in the 70's had separate processors on the mike to make sure that the levels were high enough to "squash" the stuff that was being talked over.Not usually. I'd have said that, too---but in what I've heard listening back, it was a no-talk jingle segue---previous record's fade hits 40% or so, the jingle plays, the next record with a cold open starts. If there's a tempo change, a fast to slow or slow to fast jingle aids the transition.
At one station I had no control over the audio at the engineer built his own boards. There was no level control on mikes or music sources. The idea was to set the mike hotter than music, but to avoid "pot whipping" which was all too common in that era... what Drake called, derisively, the "Bakersfield sound".
Sidebar: I had a jock at KTNQ in LA who was very fond of pot whipping, doing it five or six times just in one intro on occasion. One time, I sneaked into the studio from the newsroom door and, when he started pot whipping, I grabbed his arm and held it firmly. Besides almost having a heart attack, he never pot whipped again.
