Wind noise is at least as loud as engine noise at least at highway speeds.

While I can clearly hear my (loud piped) Ducati at 120kmh (~70mph) - on my Honda VFR800 with stock piped the engine noise is completely overshadowed by wind noise.

As a hint about how loud that wind noise gets, up around 130-140kmh, if I've got my noise cancelling earbuds in, they start clipping. I've heard them do that a handful of times in non motorcycle riding instances, always in reaction to sounds loud enough that people around look around and cover their ears.

(These days I _always_ ride with earplugs or noise cancelling earbuds in. Even on my "quiet" bikes. Gotta save that hearing damage up for loud concerts... )

Do you feel "less connected" to the world when you are riding with earplugs in? Does it make it feel more dangerous you might be less aware? It makes sense to wear the plugs, but I've never heard of a street rider doing it.

Definitely does not feel less safe. Plugs don't "disconnect" you, they just take all the sound down a few notches. The exhaust noise, wind noise, and other traffic noises are all still there, just not so loud and insistent.

I'm completely convinced that they make me safer on long rides, because you arrive significantly less tired - works great on planes too, I won't fly without earplugs any more.

While trying this tone generator out, I thought I had a ridiculous notch in my hearing at 532Hz, because the perceived volume dropped to about 10-20% of the neighbouring frequencies. But then I moved my head slightly to the side, and the normal volume was restored!

Turns out that I had inadvertently replicated a classic high-school "constructive/destructive interference" demonstration. Driving the pair of speakers on my desk at that frequency put the position of my head in one of the destructive-interference "nulls" where the effective volume approaches zero.

So if anyone else is playing around with it, be sure to use headphones instead of stereo speakers!

That's correct. Even in a factory environment, where most of the noise is in the lower frequencies, you'll still end up with a noise notch at 4 KHz. It has to do with the anatomy of the ear.