Hearing Damage over 20khz?

Frogman is right. This is exactly why analog sounds different from digital, and live instruments often sound sweeter. I have a piano in my listening room, and play acoustic and electric guitar (for over 45 years...boy are my fingers sore...) so my reference for live sound is right here. My girlfriend's Basset Hound (currently dead...the hound, not the g/f) couldn't handle my acoustic playing (even ukulele) but could sit with me when I listened to the stereo...why? I found this to be offensive and hurtful, but I think it explains something...not sure what...but something.

You cant produce a 16k square wave unless you'v got three or more octaves above that. Or more accurately upper odds of the fundamental. Damn Nyquest.

There are some that believe that having components that have a frequency response that extends beyond what is commonly accepted as the limits of human hearing has benefits. Some of those benefits are sometimes attributed to having the device not working close to limitations, and therefore working in a more comfortable, less stressful situation. Another reason suggests, that it extends the range where back reflections occur, and therefore allowing more space for dissipation of those reflections that could potentially corrupt incoming signals working within accepted hearing range.

Measurements of hearing (eg:20KHz) are based on sine waves. But lower frequency waveforms that are not sinusoidal can have wavefronts with slopes well in excess of the fundamental frequency. I believe that the ear detects wavefront slope. You may not hear a 30 KHz sine wave and yet limitation of slew rate to that corresponding to 20 KHz sine wave is audible.

I have experienced exactly this effect, except that, at my age, both frequencies are lower.

There is no evidence that the ear detects wavefront slope. The ear is like a digital device - hairs in the cochlea move and trigger nerve bundles. The on and off of the nerve bundles allows us to determine frequencies or tones. The combination of frequencies and the way they decay determines the timbre or sound.