Check out the singing the effect used here: http://www.youtube.com/watch?v=xb4M6PoI5zs&hd=1&t=112 It's an old rather obscure Queen song from a time before digital effects made spectral processing easy... Would be great to find out how they did it, and replicate the effect using music signal processing. -- I think it must be an adaptive effect.
"Stay, my love" effect