quintina

noun

1. A Sardinian vocal technique in which four performers produce an apparent fifth voice.

   “The quartet singing the liturgical music hears a fifth voice, the quintina, emerge — an acoustic effect of combined overtones, or so one might rationalize.”

   “[…] often he experiences that the performance has an excellent amalgam also without the quintina, because he can feel the situation of "mutual harmony between himself and his friends" […]”