In an article on music in New Scientist I read the following:
"In a Sardinian style of a cappela singing a fifth voice called the qunitina (literally the fifth one) emerges from four male voices when their harmony and timbres are just right. The voice is said to be that of the Virgin Mary rewarding the singers for their piety but is in fact a misperception of the chord and its harmonics "
Have you heard this? How does it work and can the technique be used with instruments to get a similar effect ?