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, "you cannot hear beyond 20kHz so ignore my pet! and let it run free." And we did, but still, we could smell its scorched earth and feel the pain inflicted by this unseen devil as it defiled all in its wake.
So strong was the sorcerer's spell—the engineer's curse—that we searched for the cause of this added harshness in every place but where it was. And then, one day, it became known to us that its work was invisible. That while it frolicked unseen in the amplifier, everything else was straining under its weight, doing battle, trying to stay true to the music. The harshness we heard was because the amp's temple of purity was bombarded by this ultrasonic nightmare and once we put a gate at the amp's entrance the beast could no longer enter, and music became heaven! The sweetness returned when the battle ended.
We had broken the sorceress' spell, ignored her words, and crafted beauty, finally free of the beast that hid inside the amp.
All for $0.20 in parts and years of pain and searching.
