Equalization

Unfortunately there is also quite a bit of snake oil being peddled. As for room acoustics and equalization, including some useful links: https://forum.audiogon.com/discussions/room-acoustics-10

bstbomber,  I still remember that I had to constantly adjust my old inexpensive receiver's controls.  It was either too bassy, too veiled, too bright etc.  Almost every CD needed some adjustment.  Today, with better source, amp and speakers I don't need to adjust anything.  I also noticed that the cheapest boom boxes have all sorts of controls including graphic equalizers. There is a reason for that.  Tone controls don't improve transparency and don't come for free.  Same goes for balance control, (that I don't need).  I like to listen to music the way it was intended.

In the most expensive manner possible.

Snake oil is good for the hobby. 🐍 It greases the wheels of progress and makes everything run smoother. Obviously not everyone is on board the progress train and that’s OK. 🚂

The best use of tone controls (which went out-of-fashion in high-end in the 70's) is to correct for the differing balances found in recordings. The Quad pre-amps had (have?) great ones.