Sundberg Hefele Lindblom Overtone singingn
Channel: johan sundberg
Date: 13/05/2020

Voice Source and Articulation of Overtone Singing
A Case Study 
Johan Sundberg, PhD, KTH, SMI, Stockholm University
Anna Maria Hefele, Singer
Björn Lindblom, PhD, Stockholm University

ABSTRACT
Overtone singing is produced by a single artist in such a way that two simultaneously sounding pitches are perceived, a drone plus a strong overtone. Acoustically the spectrum typically contains a complete set of harmonic partials, one of which is 10 to 20 dB stronger than its neighbors.  
 
According to Bloothoft and associates [1] the boosting of the overtone can be explained as the consequence of clustering the second and third formants. Klingholz [2] pointed out that the effect can be explained by a super-narrow bandwidth of a formant coinciding with the enhanced partial. It also has been suggested that non-linear source-filter interaction plays an important role.  
 
The acoustic characteristics of vocal sounds are determined by the voice source, which is produced by the pulsating glottal airflow, and the sound transfer properties of the vocal tract. The aim of the present case study was to find out to what extent source-filter interaction or a super-narrow formant bandwidth are necessary to explain the production of overtone singing.  
 
Examples of overtone singing were recorded, where a professional singer specializing in this technique (coauthor AMH) enhanced partials number 4 to 10. The recording was analyzed by inverse filtering, which does not model any source-filter interaction. The results showed that the radiated spectrum could be explained as a consequence of clustering the second and third formants close to the enhanced partial, as suggested by Bloothoft et al 1992 [1]; the source spectrum envelope did not show any enhancement of this partial. In other words, neither source-filter interaction, nor a super-narrow formant bandwidth were needed for explaining this overtone singing within the limits of normal voice production.  
 
Inspection of an Internet MR movie documentation of the same artist [3] shows that she produced the overtone singing with an elevated tongue tip, the position of which is moved anteriorly with increasing frequency of the prominent overtone. In this way, a cavity is formed anterior to the tongue tip, complemented by a narrow lip opening, i.e., Helmholtz type resonator.  Such a front cavity has been shown to typically determine the frequency of the third formant [4]. Attempts will be made to test the assumption that this overtone singer’s front cavity can be approximated as a resonator with a resonance frequency just above the frequency of the enhanced partial.  
 
The results presently gained support the conclusion that overtone singing can be interpreted as a purely resonatory phenomenon produced by means of clustering the second and third formants with normal bandwidths just below and just above the enhanced partial.  
 
 
 
 
Johan Sundberg, PhD, Dept of Speech Music Hearing, School of electrical engineering and Computer Science, KTH, SE-10044 Stockholm Sweden and University College of Music Education Stockholm,  jsu@kth.se, +46707407873 
 
Anna-Maria Hefele, Schärdingerstr. 28, A-4774 St. Marienkirchen, Austria, +43 660/2011509, ama@annamaria-hefele.com 
 
Björn Lindblom, PhD, Dept of Linguistics, Stockholm University, SE- 106 91 Stockholm, Sweden, +705403669, lindblom@ling.su.se 
 
References 
[1] Bloothooft G1, Bringmann E, van Cappellen M, van Luipen JB, Thomassen KP. Acoustics and perception of overtone singing. J Acoust Soc Am. 1992 Oct; 92 (4 Pt 1):1827-36 
[2] Klingholz F. Overtone Singing: Productive Mechanisms and Acoustic Data. Journal of Voice 7: 2, 118-122  
[3] MR movie produced at the Freiburger Institut für Musikermedizin by prof. B Richter, prof M Echternach and Dr.-Ing M Burdumi, available at https://youtu.be/-jKl61Xxkh0  
[4] Sundberg J, Lindblom B. Acoustic estimation of the front cavity in apical stops. J Acoust Soc Amer 88 1990, 1313-1317.