Interesting look at THD

Oh Oh. Did I forget the link??
Whoops, I'll get it. (a bit sheep-ishly). 

https://ewh.ieee.org/r3/nashville/events/2005/Harmonics_MCPQG_IEEE_2005.pdf

Yes. You need to read well into the article to get to the parts
that I find interesting, relative to audio system distortions and remedies.

It's also interesting how much of the noise rides on the neutral conduction; and that for switch mode power supplies the neutral wire should be about 1.7 times that of the conductors. ( I wonder if this is so in the 'switch mode' supplies in audio equipment)
I've also found it interesting that many manufacturers of noise reduction products insist theirs should not be used with other manufacturers devices. My experience does not support this dictate and in fact I've found different products can be very complementary; depending of course on where and how used. Also, I can't imagine anyone arguing with 'balanced power' ;say Equitech Q transformer based products, properly sized, being anything but a significant benefit to most audio systems. The electrical math appears inarguable to me;but I'm open to learning.  

Thanks randy.It's the review of concepts I find interesting. Also the cost/benefit graphs.
The way that skin depth of the conductor varies with frequency
also surprised me. (I don't have an EE or similar background).
This business of  voltage noise attenuation appears very complex/interesting. I feel the increasing capabilities/speeds of computers will ultimately allow better analysis of the instantaneous effects of various interactions and give us significant improvements over whats practically available today.