"A "speed up circuit" for audio signal? Why? It gets there fast enough."
No it is digital O and 1 plus crap not analogue. Check edges, over shoot, ringing to name a few.
Oh and 0.5C(V*V) for stored energy thus time to fill and empty the bucket.
Lets face it 50yrs ago we as students were told that telephone line bandwidth could only be 5KHz whoops that was wrong and before that the Earth was flat, yes still true in some minds.
Our kids here in the UK were told by teachers that the Adder a snake was not poisonous, poop wrong again.
So stop closing you minds and question your teachers they are not always correct. The passing on of knowledge is like a story and over the years bits get added and removed and facts are the same not every teacher passes on correct facts just the small bit he or she understands.
Oh you can buy blindfolds on ebay
https://www.ebay.co.uk/itm/BLACK-EYE-MASK-sleep-blindfold-sleeping-eyemask-/350203809473