Nonlinear source–filter coupling in phonation: Vocal exercises

Abstract

Nonlinear source-filter coupling has been demonstrated in computer simulations, in excised larynx experiments, and in physical models, but not in a consistent and unequivocal way in natural human phonations. Eighteen subjects ͑nine adult males and nine adult females͒ performed three vocal exercises that represented a combination of various fundamental frequency and formant glides. The goal of this study was to pinpoint the proportion of source instabilities that are due to nonlinear source-tract coupling. It was hypothesized that vocal fold vibration is maximally destabilized when F 0 crosses F 1 , where the acoustic load changes dramatically. A companion paper provides the theoretical underpinnings. Expected manifestations of a source-filter interaction were sudden frequency jumps, subharmonic generation, or chaotic vocal fold vibrations that coincide with F 0 -F 1 crossovers. Results indicated that the bifurcations occur more often in phonations with F 0 -F 1 crossovers, suggesting that nonlinear source-filter coupling is partly responsible for source instabilities. Furthermore it was observed that male subjects show more bifurcations in phonations with F 0 -F 1 crossovers, presumably because in normal speech they are less likely to encounter these crossovers as much as females and hence have less practice in suppressing unwanted instabilities.

Air sacs and vocal fold vibration: Implications for evolution of speech

“…It can be observed that the dip in output power of the hard-walled air sac occurs almost exactly at the location where the resonance frequency of the vocal tract crosses the preferred frequency of the vocal folds. This concurs with the observations by Titze et al (Titze 2008 on tracts without air sacs. There also appear to be relations between irregular vocalization and the crossing of the third harmonic and the resonance frequency of the tract 24 Bart de Boer with hard-walled air sacs, and between onset of irregularity and crossing of the second harmonic and the resonance frequency of the tract with softwalled air sacs.…”

“…Another way in which the interaction between the vocal folds and the vocal tract can be increased is by decreasing the diameter of the epilaryngeal tube (Titze 2008;Titze et al 2008). This is the part of the supralaryngeal vocal tract just above the vocal folds, and its diameter can be controlled by actions of the pharyngeal muscles.…”

Investigating acoustic correlates of human vocal fold vibratory phase asymmetry through modeling and laryngeal high-speed videoendoscopy

“…Additional model features, however, are implemented that are fundamental to the present acoustic investigation. In particular, nonlinear source-filter coupling between subglottal and supraglottal tracts is incorporated to account for acoustic coupling that has been shown to significantly affect source properties and system dynamics (Story and Titze, 1995;Zañartu et al, 2007;Titze et al, 2008;Titze, 2008). This coupling allows for observing the well-documented pulse skewing of the glottal airflow waveform, which is critical for determining spectral tilt and other acoustic characteristics (Doval and d'Alessandro, 2006).…”

Σύνθεση Φωνής Με Υπολογιστική Αεροδυναμική Ανάλυση Του Ανθρωπινού Ηχητικού Σωλήνα Και Σύγκριση Με Κλασσικές Μεθόδους

“…Οι πειραματικές αυτές ενδείξεις επιβεβαιώνονται επίσης από προσομοιώσεις της αεροακουστι-κής του φωνητικού σωλήνα [106,188,189,145,173]. Παράλληλα, άλλες μελέτες έχουν επίσης δείξει μη-γραμμική ακουστική σύζευξη μεταξύ της πηγής ήχου στην γλωττίδα και της φωνητικής οδού [2,57,162,161,163] Επομένως, γίνεται φανερό πως η απάντηση στο ερώτημα είναι καταφατική. Αυτό όμως που έχει σημασία να διερευνήσουμε σε μεγαλύτερο βάθος, είναι αρχικά την συχνότητα και τον τρόπο εμφάνισης μη-γραμμικών φαινομένων στο σήμα της φωνής, και εν συνεχεία την επίπτωση αυτών στην ακουστική επεξεργασία για εφαρμογές φωνής.…”

“…Πειράματα με αριθμητικές προσομοιώσεις έχουν επιβεβαιώσει την εμφάνιση μη γραμμικών φαινομένων [106,188,189,145,173]. Επιπλέον πολλές άλλες μελέτες έχουν δείξει ότι υπάρχει μια μη-γραμμική σύζευξη μεταξύ της γλωττιδικής πηγής και του φωνητικού σωλήνα [2,57,162,161,163].…”