The audio quality of some pilots is just terrible but somehow they know wtf they said.

That is in my experience highly dependent on what kind of radio/antenna is used to record the live broadcast, it's orientation and it's location.

I have an Icom IC-R6 radio scanner, even at the airport with line of sight of the infrastructure you can still get a terrible reception if the angle of the radio is wrong, the antenna is wrong or you have parked in the wrong spot.