I find it very useful to play famous speakers' in twice the speed.
The Scripture says we must be quick to listen, slow to speak (James 1:19). While many speakers learned to speak slowly to prove clarity and calmness, they cannot truly hide their aggressive emotions. By double speeding their talks, I noticed certain anxiety in some voices which would be undetected by amateur like me had it been played at the normal speed.
Listening from Tim Keller to MacArthur to Mefferd, I could tell, though Mefferd learned a habit of speaking slowly, she is aggressively talkative; While the other two sounded calm and casual even at twice the speed played.