My first major crime in life was pressing the emergency stop button on an escalator, much to the horror and shame of my poor mother, as every face on that escalator turned and scowled right at her son.

The second time I saw a button that I wanted to press, it was marked Loudness, 

This was on my new Kenwood integrated amplifier in the 1970s. I hadn’t a clue what the button actually did, but what stereo lover doesn’t want more loudness?

I pushed it.

The sound became richer, fuller, and more exciting. Push it again and everything went dry and thin.

This was not a difficult decision. The button stayed in.

What I didn’t understand was that it wasn’t really making the system louder. It was compensating for the way our hearing changes at low listening levels. As the volume drops, we perceive less bass and treble even though a microphone measuring the system sees something different.

The loudness circuit gave the ear a helping hand by boosting the frequency extremes. As the volume went up, the boost went down until it eventually disappeared.

Clever.

You don’t see loudness controls on much high-end equipment today. Adding phase-shifting circuitry has a sonic cost, and most high-performance systems aren’t designed to spend their lives whispering in the background.

Still, I miss that button.

It was technically impure, shamelessly entertaining, and for a young stereo nut with a new Kenwood, absolutely irresistible.

Sometimes knowing better is less fun.