Here's the thing. I often listen to recorded voices at 1.25x or 1.50x speedup. Some people can be easily understood faster, others not. A commonality in those that can be understood are they are professionals, and ones that can't are lay people. Clearly (!), the professionals enunciate in a way that's much more understandable.

I've also noticed when listening to a presentation that some presenters are a lot easier to listen to. I'd like to improve my presentations in that way - that means tone, pacing, enunciation, etc.