I still shoot for good intonation, but I don't know how I can set the bar very high when I keep running across sound bites in videos where someone invariably says, "you should be able to hear the difference there"!   

...noooooooooo I couldn't! 

Well, found out a few things - first, I shouldn't be listening with my old laptop speakers!!! 

...then I ran across some very cool stuff about sound & music. 

The M.C.Escher of Music? (David Bruce Composer) 

Casey Connor has more than this wonderful series of 14 videos on his YT Channel (check it out) - 'Psycho-acoustics / Audio Illusions' (Playlist)

Part 7/5!

The best one to start watching clarifies some things with updates & corrections.  Chapters are time-stamped for all videos.

An additional consideration (not mentioned in the video) in terms of your playback system: you need to listen to the 720p version or better -- the lower-quality streams degrade the audio (including the stereo separation).

Part 3/5!  

There's some stuff in this video to make me want to think twice when I'm trying to learn some music by ear!

Okay, maybe I'll consider wearing headphones!