Digesting all the info on that site will take years to really understand it
a simple Radio Shack meter will register all the model noises--close enough for folk music
those who have a formal musical education ,at one time labored thru the basics of first getting a sound -then a recognizable sound - then a pleasant sound --from their first musical instrument
Been there since age 7 -and I started late!

I learned to detect rpm -by simply hearing the pitch of the engine noise.

absoute rpm readings -no - but relative rpm yes.
I was doing tests one day and a friend noted I said a particular rpm was about so much higher than the last one.
He asked" how can you tell?"
I said "because the pitch was relatively so much higher ."
He did not know that pitch and rpm went hand in hand-and frankly - with him having no background in music -I understood the question.
Anyway - that site has lots of info -but spend a little time with a Radio Shack meter - you will soon see the relationship of noises /frequencies etc..
This is one place where experience REALLY counts