Hope this is an OK place for this topic. I'm sure the moderators will move it if not.
About Glenn Drodge's email concerning angelic harmony, I know what he means about hitting harmonies just right and having it sound angelic. I also have cause to attempt singing in the best possible harmony, and now that I think of it, for years we've been saying "like angels" when we high it just right.
But I can't get my mind around Glenn's theory of an added harmonic. How can that be?
Every voice that is singing is producing a waveform that consists of a fundamental and some combination of harmonics... just a combination of sinusiods with related frequencies. No matter how many voices singing, there are just a bunch of sin waves being produced from each voice. I don't see how there can be any added harmonic (new frequency sin wave that is not a fundamtal or harmonic being produced by one of the singers) that pops up just because poeple are controlling their pitches particularly well.
One thing that might be happening is that as people sing their pitches more perfectly, the beat frequencies they produce when two or more singers produce a same sinusoid will be less and less evident. This can only make the harmony sound better.
Another thing that comes to mind is that all the sin waves flying around will combine and might create new-sounding waveforms that won't necessarily sound like any one singer's voice.
There also might be some interesting and beautiful sounding phase shifting effects in play when singers sing very close harmony. Vocal processing techniques sometimes involve combining a vocal signal with a slightly detuned version of the same signal. Some of the resulting sounds might be described as angelic.
It's also true that human hearing is a pretty wacky thing, what with our brains involved and all. Check out how "perceptual" codecs such as MP3 work. Maybe something along these lines relates in some way. That I can't think of.
Of course, none of what I've suggested could be "the answer" to angelic harmony either. But I'm pretty sure no new harmonics are popping up on their own.