JOHAN SUNDBERG, BJÖRN LINDBLOM, and ANNA-MARIA HEFELE : One-Singer-Two-Voices Click to access One-Singer-Two-Voices-Johan-Sundberg.pdf https://acousticstoday.org/wp-content/uploads/2021/03/One-Singer-Two-Voices-Johan-Sundberg
TRAN QUANG HAI's world throat singing 