40 years ago we added defenses against an unseen enemy: a scourge of fidelity, an attack on musicality. We couldn't see this demon but we certainly knew of its impacts. It was pervasive, heard but hidden. A layer of added grit and pain to the music.
A $0.20 sword was all it took to slay the beast. Our weapon of choice was a single small capacitor placed at the input of our power amplifiers.
The enemy within had a name: ultrasonics, and we had ignored it because an evil sorceress had cast a spell upon us. She waved her calculator and said,