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Formant frequencies and bandwidths of the vocal tract transfer function are affected by the mechanical impedance of the vocal tract wall.

Fleischer M, Pinkert S, Mattheus W, Mainka A, Mürbe D - Biomech Model Mechanobiol (2014)

Bottom Line: The values of the normalised inertial component (represented by the imaginary part of the impedance) ranged from 250 g/m(2) at frequencies higher than about 3 kHz up to about 2.5 × 10(5) g/m(2)in the mid-frequency range around 1.5-3 kHz.In contrast, the normalised dissipation (represented by the real part of the impedance) ranged from 65 to 4.5 × 10(5) Ns/m(3).These results indicate that structures enclosing the vocal tract (e.g. oral and pharyngeal mucosa and muscle tissues), especially their mechanical properties, influence the transfer of the acoustical energy and the position and bandwidth of the formant frequencies.

View Article: PubMed Central - PubMed

Affiliation: Department of Otorhinolaryngology, Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany, mario.fleischer@uniklinikum-dresden.de.

ABSTRACT
The acoustical properties of the vocal tract, the air-filled cavity between the vocal folds and the mouth opening, are determined by its individual geometry, the physical properties of the air and of its boundaries. In this article, we address the necessity of complex impedance boundary conditions at the mouth opening and at the border of the acoustical domain inside the human vocal tract. Using finite element models based on MRI data for spoken and sung vowels /a/, /i/ and /Ω(-1)/ and comparison of the transfer characteristics by analysis of acoustical data using an inverse filtering method, the global wall impedance showed a frequency-dependent behaviour and depends on the produced vowel and therefore on the individual vocal tract geometry. The values of the normalised inertial component (represented by the imaginary part of the impedance) ranged from 250 g/m(2) at frequencies higher than about 3 kHz up to about 2.5 × 10(5) g/m(2)in the mid-frequency range around 1.5-3 kHz. In contrast, the normalised dissipation (represented by the real part of the impedance) ranged from 65 to 4.5 × 10(5) Ns/m(3). These results indicate that structures enclosing the vocal tract (e.g. oral and pharyngeal mucosa and muscle tissues), especially their mechanical properties, influence the transfer of the acoustical energy and the position and bandwidth of the formant frequencies. It implies that the timbre characteristics of vowel sounds are likely to be tuned by specific control of relaxation and strain of the surrounding structures of the vocal tract.

No MeSH data available.


Related in: MedlinePlus

Formant bandwidth as function of formant frequencies for the vowels /a/ and /i/ as denoted in each diagram. Dark blue symbols correspond to spoken vowels and red symbols to sung vowels, respectively. As shown with circles, there is partly a large discrepancy to the values determined by the inverse filtering method (DECAP, denoted with diamonds) for the model values assuming acoustically hard VT walls (denoted with circles). In contrast, as denoted by stars, the models can be significantly improved by introducing the complex impedance of the VT wall. For comparison, the fitting functions given by Hawks and Miller (1995) are shown with black solid lines. For the vowel //, the bandwidths in case of rigid walls are all very small. Due to the nearly closed lips, the damping of outgoing waves is not sufficient to generate more realistic bandwidths
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Fig8: Formant bandwidth as function of formant frequencies for the vowels /a/ and /i/ as denoted in each diagram. Dark blue symbols correspond to spoken vowels and red symbols to sung vowels, respectively. As shown with circles, there is partly a large discrepancy to the values determined by the inverse filtering method (DECAP, denoted with diamonds) for the model values assuming acoustically hard VT walls (denoted with circles). In contrast, as denoted by stars, the models can be significantly improved by introducing the complex impedance of the VT wall. For comparison, the fitting functions given by Hawks and Miller (1995) are shown with black solid lines. For the vowel //, the bandwidths in case of rigid walls are all very small. Due to the nearly closed lips, the damping of outgoing waves is not sufficient to generate more realistic bandwidths

Mentions: As an initial step of our work, we determined the relevant acoustical data of the VT, which means the formant frequencies and the bandwidths. We focussed on the first five formants which are of great interest for the perception of vowel quality and timbre. The results of the analysis using an inverse filtering method are shown in Table 1. It is obvious that the first three formants and bandwidths for the vowel /a/ are only slightly affected by the mode of voice production (9 Hz in formant frequencies and 19 Hz in bandwidths), which means that there is no great difference between the singing or speech mode. The differences in the acoustical characteristics are greater for the fourth and fifth formant (150 Hz) which is caused by the higher sensitivity to small geometric variations and/or physical properties of the VT by diminishing the wavelength. The results for the vowel /i/ are similar, but in contrast to the vowel /a/, and there is already an distinguished difference in the second formant in the order of 100 Hz observable, but the first and the third formant frequency (and their associated bandwidth) are nearly unaffected by the mode of voice production. Similar to vowel /a/, the fourth and the fifth formant are shifted in the singing mode relative to their position in case of the spoken vowel. For vowel //, the first three formant frequencies were slightly greater in singing mode, whereas the associated bandwidths were only slightly affected. A substantial difference of more than 500 Hz between the singing and speech mode was found at F5. This indicates that in the speech mode at about 3.5 kHz, a resonance was suppressed rather than a shift of a formant occurred. Summarising these (intermediate) data, in comparison with an overview given in Hawks and Miller (1995) and graphically shown in Fig. 8 (denoted with diamonds), the relationship between the formant frequencies and the bandwidth is in a plausible order of magnitude.


Formant frequencies and bandwidths of the vocal tract transfer function are affected by the mechanical impedance of the vocal tract wall.

Fleischer M, Pinkert S, Mattheus W, Mainka A, Mürbe D - Biomech Model Mechanobiol (2014)

Formant bandwidth as function of formant frequencies for the vowels /a/ and /i/ as denoted in each diagram. Dark blue symbols correspond to spoken vowels and red symbols to sung vowels, respectively. As shown with circles, there is partly a large discrepancy to the values determined by the inverse filtering method (DECAP, denoted with diamonds) for the model values assuming acoustically hard VT walls (denoted with circles). In contrast, as denoted by stars, the models can be significantly improved by introducing the complex impedance of the VT wall. For comparison, the fitting functions given by Hawks and Miller (1995) are shown with black solid lines. For the vowel //, the bandwidths in case of rigid walls are all very small. Due to the nearly closed lips, the damping of outgoing waves is not sufficient to generate more realistic bandwidths
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4490178&req=5

Fig8: Formant bandwidth as function of formant frequencies for the vowels /a/ and /i/ as denoted in each diagram. Dark blue symbols correspond to spoken vowels and red symbols to sung vowels, respectively. As shown with circles, there is partly a large discrepancy to the values determined by the inverse filtering method (DECAP, denoted with diamonds) for the model values assuming acoustically hard VT walls (denoted with circles). In contrast, as denoted by stars, the models can be significantly improved by introducing the complex impedance of the VT wall. For comparison, the fitting functions given by Hawks and Miller (1995) are shown with black solid lines. For the vowel //, the bandwidths in case of rigid walls are all very small. Due to the nearly closed lips, the damping of outgoing waves is not sufficient to generate more realistic bandwidths
Mentions: As an initial step of our work, we determined the relevant acoustical data of the VT, which means the formant frequencies and the bandwidths. We focussed on the first five formants which are of great interest for the perception of vowel quality and timbre. The results of the analysis using an inverse filtering method are shown in Table 1. It is obvious that the first three formants and bandwidths for the vowel /a/ are only slightly affected by the mode of voice production (9 Hz in formant frequencies and 19 Hz in bandwidths), which means that there is no great difference between the singing or speech mode. The differences in the acoustical characteristics are greater for the fourth and fifth formant (150 Hz) which is caused by the higher sensitivity to small geometric variations and/or physical properties of the VT by diminishing the wavelength. The results for the vowel /i/ are similar, but in contrast to the vowel /a/, and there is already an distinguished difference in the second formant in the order of 100 Hz observable, but the first and the third formant frequency (and their associated bandwidth) are nearly unaffected by the mode of voice production. Similar to vowel /a/, the fourth and the fifth formant are shifted in the singing mode relative to their position in case of the spoken vowel. For vowel //, the first three formant frequencies were slightly greater in singing mode, whereas the associated bandwidths were only slightly affected. A substantial difference of more than 500 Hz between the singing and speech mode was found at F5. This indicates that in the speech mode at about 3.5 kHz, a resonance was suppressed rather than a shift of a formant occurred. Summarising these (intermediate) data, in comparison with an overview given in Hawks and Miller (1995) and graphically shown in Fig. 8 (denoted with diamonds), the relationship between the formant frequencies and the bandwidth is in a plausible order of magnitude.

Bottom Line: The values of the normalised inertial component (represented by the imaginary part of the impedance) ranged from 250 g/m(2) at frequencies higher than about 3 kHz up to about 2.5 × 10(5) g/m(2)in the mid-frequency range around 1.5-3 kHz.In contrast, the normalised dissipation (represented by the real part of the impedance) ranged from 65 to 4.5 × 10(5) Ns/m(3).These results indicate that structures enclosing the vocal tract (e.g. oral and pharyngeal mucosa and muscle tissues), especially their mechanical properties, influence the transfer of the acoustical energy and the position and bandwidth of the formant frequencies.

View Article: PubMed Central - PubMed

Affiliation: Department of Otorhinolaryngology, Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany, mario.fleischer@uniklinikum-dresden.de.

ABSTRACT
The acoustical properties of the vocal tract, the air-filled cavity between the vocal folds and the mouth opening, are determined by its individual geometry, the physical properties of the air and of its boundaries. In this article, we address the necessity of complex impedance boundary conditions at the mouth opening and at the border of the acoustical domain inside the human vocal tract. Using finite element models based on MRI data for spoken and sung vowels /a/, /i/ and /Ω(-1)/ and comparison of the transfer characteristics by analysis of acoustical data using an inverse filtering method, the global wall impedance showed a frequency-dependent behaviour and depends on the produced vowel and therefore on the individual vocal tract geometry. The values of the normalised inertial component (represented by the imaginary part of the impedance) ranged from 250 g/m(2) at frequencies higher than about 3 kHz up to about 2.5 × 10(5) g/m(2)in the mid-frequency range around 1.5-3 kHz. In contrast, the normalised dissipation (represented by the real part of the impedance) ranged from 65 to 4.5 × 10(5) Ns/m(3). These results indicate that structures enclosing the vocal tract (e.g. oral and pharyngeal mucosa and muscle tissues), especially their mechanical properties, influence the transfer of the acoustical energy and the position and bandwidth of the formant frequencies. It implies that the timbre characteristics of vowel sounds are likely to be tuned by specific control of relaxation and strain of the surrounding structures of the vocal tract.

No MeSH data available.


Related in: MedlinePlus