My dad was a film and sound editor. Back in those days it was all film and lots of care was taken to get it right because unlike digital, you couldn't fix it on the fly and had to reshoot. Set up was done right the first time, all the time. Any clean up done in post production was a chore in itself.
Not liking the quality of the sound on most of the library that the studios had, my dad would be his own foley and make better recordings of sound effects to use in his work. Sometimes he'd step in and do 2nd director work if they were short handed. He even doubled for Anthony Quinn for The Man and the City for back and side shots if some small scene had to be reshot. He looked like a cross between Jason Robards and Anthony Quinn (quite the handsome rascal).
Anyway, he tried to get me a job and for half a year I'd go in for an hour before my regular job to learn the ropes on sound editing. It was just an entry level job where I'd clean the heads of the giant recorders, put on the music reel, the dialogue reel and the sound effects reel and synchronize them for the lead guy to patch it all into the big room where they'd play it all back, adjusting levels, until they were satisfied.
I'd go in and watch them do it and once there was a quarrel between two execs and one of them was being a prick about what couldn't hear. The other guy was incredulous and so was I. Here I am, all the way in the back of a massive theater and I could hear everything but this tool was sabotaging the other guys work. It happens more than you know. So there's that aspect to consider. But even with that, I've never seen a movie shot on film where I couldn't understand the dialogue. This article rings so true about modern day digital shooting, lazy actors, and what seems like lower standards in some respects when it comes to audience consideration.
I remember my dad lamenting the advent of digital. He saw it as flat, lifeless, stark and hard to work with, but that was in it's infancy and they had a long way to go before they got it right.
All the best,
Nonoise