IF you can hear the difference than it CAN be measured!
If we know what to measure, and how. We're not quite there yet. There's this pesky property of sound called "timbre". It ain't so easily measured.

Not trying to give you a hard time Bill, just trying to illustrate that the parameters of sound are not as "black and white" simple as they're often represented.

I'd like to see the measurement of what a seasoned guitarist who can blindly tell the difference between a pre-wwII, and post-wwII Martin acoustic guitar hears, and how such a measurement would be obtained.