What do bass and treble controls do?

We've all seen the old bass and treble controls on vintage (and sometimes modern) equipment. What do they actually do and how should they be used? Have a question you want to ask Paul? http://www.psaudio.com/ask-paul/ I am getting close to publishing my memoir! It's called 99% True and it is chock full of adventures, debauchery, struggles, heartwarming stories, triumphs and failures, great belly laughs, and a peek inside the high-end audio industry you've never known before. I plan a few surprises for early adopters, so go to https://www.paulmcgowan.com and add your name to the list of interested readers. There's an entire gallery of never before seen photos too.